* [PATCHv3 0/6] zswap: compressed swap caching
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
Changelog:
v3:
* Dropped the zsmalloc patches from the set, except the promotion patch
which has be converted to a rename patch (vs full diff). The dropped
patches have been Acked and are going into Greg's staging tree soon.
* Separated [PATCHv2 7/9] into two patches since it makes changes for two
different reasons (Minchan)
* Moved ZSWAP_MAX_OUTSTANDING_FLUSHES near the top in zswap.c (Rik)
* Rebase to v3.8-rc5. linux-next is a little volatile with the
swapper_space per type changes which will effect this patchset.
* TODO: Move some stats from debugfs to sysfs. Which ones? (Rik)
v2:
* Rename zswap_fs_* functions to zswap_frontswap_* to avoid
confusion with "filesystem"
* Add comment about what the tree lock protects
* Remove "#if 0" code (should have been done before)
* Break out changes to existing swap code into separate patch
* Fix blank line EOF warning on documentation file
* Rebase to next-20130107
Zswap Overview:
Zswap is a lightweight compressed cache for swap pages. It takes
pages that are in the process of being swapped out and attempts to
compress them into a dynamically allocated RAM-based memory pool.
If this process is successful, the writeback to the swap device is
deferred and, in many cases, avoided completely. This results in
a significant I/O reduction and performance gains for systems that
are swapping.
The results of a kernel building benchmark indicate a
runtime reduction of 53% and an I/O reduction 76% with zswap vs normal
swapping with a kernel build under heavy memory pressure (see
Performance section for more).
Some addition performance metrics regarding the performance
improvements and I/O reductions that can be achieved using zswap as
measured by SPECjbb are provided here:
http://ibm.co/VCgHvM
These results include runs on x86 and new results on Power7+ with
hardware compression acceleration.
Of particular note is that zswap is able to evict pages from the compressed
cache, on an LRU basis, to the backing swap device when the compressed pool
reaches it size limit or the pool is unable to obtain additional pages
from the buddy allocator. This eviction functionality had been identified
as a requirement in prior community discussions.
Patchset Structure:
1: add atomic_t get/set to debugfs
2: promote zsmalloc to /lib
3,4: changes to existing swap code for zswap
5,6: add zswap and documentation
Rationale:
Zswap provides compressed swap caching that basically trades CPU cycles
for reduced swap I/O. This trade-off can result in a significant
performance improvement as reads to/writes from to the compressed
cache almost always faster that reading from a swap device
which incurs the latency of an asynchronous block I/O read.
Some potential benefits:
* Desktop/laptop users with limited RAM capacities can mitigate the
performance impact of swapping.
* Overcommitted guests that share a common I/O resource can
dramatically reduce their swap I/O pressure, avoiding heavy
handed I/O throttling by the hypervisor. This allows more work
to get done with less impact to the guest workload and guests
sharing the I/O subsystem
* Users with SSDs as swap devices can extend the life of the device by
drastically reducing life-shortening writes.
Compressed swap is also provided in zcache, along with page cache
compression and RAM clustering through RAMSter. Zswap seeks to deliver
the benefit of swap compression to users in a discrete function.
This design decision is akin to Unix design philosophy of doing one
thing well, it leaves file cache compression and other features
for separate code.
Design:
Zswap receives pages for compression through the Frontswap API and
is able to evict pages from its own compressed pool on an LRU basis
and write them back to the backing swap device in the case that the
compressed pool is full or unable to secure additional pages from
the buddy allocator.
Zswap makes use of zsmalloc for the managing the compressed memory
pool. This is because zsmalloc is specifically designed to minimize
fragmentation on large (> PAGE_SIZE/2) allocation sizes. Each
allocation in zsmalloc is not directly accessible by address.
Rather, a handle is return by the allocation routine and that handle
must be mapped before being accessed. The compressed memory pool grows
on demand and shrinks as compressed pages are freed. The pool is
not preallocated.
When a swap page is passed from frontswap to zswap, zswap maintains
a mapping of the swap entry, a combination of the swap type and swap
offset, to the zsmalloc handle that references that compressed swap
page. This mapping is achieved with a red-black tree per swap type.
The swap offset is the search key for the tree nodes.
Zswap seeks to be simple in its policies. Sysfs attributes allow for
two user controlled policies:
* max_compression_ratio - Maximum compression ratio, as as percentage,
for an acceptable compressed page. Any page that does not compress
by at least this ratio will be rejected.
* max_pool_percent - The maximum percentage of memory that the compressed
pool can occupy.
To enabled zswap, the "enabled" attribute must be set to 1 at boot time.
Zswap allows the compressor to be selected at kernel boot time by
setting the “compressor” attribute. The default compressor is lzo.
A debugfs interface is provided for various statistic about pool size,
number of pages stored, and various counters for the reasons pages
are rejected.
Performance, Kernel Building:
Setup
========
Gentoo w/ kernel v3.7-rc7
Quad-core i5-2500 @ 3.3GHz
512MB DDR3 1600MHz (limited with mem=512m on boot)
Filesystem and swap on 80GB HDD (about 58MB/s with hdparm -t)
majflt are major page faults reported by the time command
pswpin/out is the delta of pswpin/out from /proc/vmstat before and after
the make -jN
Summary
========
* Zswap reduces I/O and improves performance at all swap pressure levels.
* Under heavy swaping at 24 threads, zswap reduced I/O by 76%, saving
over 1.5GB of I/O, and cut runtime in half.
Details
========
I/O (in pages)
base zswap change change
N pswpin pswpout majflt I/O sum pswpin pswpout majflt I/O sum %I/O MB
8 1 335 291 627 0 0 249 249 -60% 1
12 3688 14315 5290 23293 123 860 5954 6937 -70% 64
16 12711 46179 16803 75693 2936 7390 46092 56418 -25% 75
20 42178 133781 49898 225857 9460 28382 92951 130793 -42% 371
24 96079 357280 105242 558601 7719 18484 109309 135512 -76% 1653
Runtime (in seconds)
N base zswap %change
8 107 107 0%
12 128 110 -14%
16 191 179 -6%
20 371 240 -35%
24 570 267 -53%
%CPU utilization (out of 400% on 4 cpus)
N base zswap %change
8 317 319 1%
12 267 311 16%
16 179 191 7%
20 94 143 52%
24 60 128 113%
Seth Jennings (6):
debugfs: add get/set for atomic types
zsmalloc: promote to lib/
mm: break up swap_writepage() for frontswap backends
mm: allow for outstanding swap writeback accounting
zswap: add to mm/
zswap: add documentation
Documentation/vm/zswap.txt | 73 ++
drivers/staging/Kconfig | 2 -
drivers/staging/Makefile | 1 -
drivers/staging/zcache/zcache-main.c | 3 +-
drivers/staging/zram/zram_drv.h | 3 +-
drivers/staging/zsmalloc/Kconfig | 10 -
drivers/staging/zsmalloc/Makefile | 3 -
fs/debugfs/file.c | 42 +
include/linux/debugfs.h | 2 +
include/linux/swap.h | 4 +
.../staging/zsmalloc => include/linux}/zsmalloc.h | 0
lib/Kconfig | 18 +
lib/Makefile | 1 +
.../zsmalloc/zsmalloc-main.c => lib/zsmalloc.c | 3 +-
mm/Kconfig | 15 +
mm/Makefile | 1 +
mm/page_io.c | 22 +-
mm/swap_state.c | 2 +-
mm/zswap.c | 1073 ++++++++++++++++++++
19 files changed, 1250 insertions(+), 28 deletions(-)
create mode 100644 Documentation/vm/zswap.txt
delete mode 100644 drivers/staging/zsmalloc/Kconfig
delete mode 100644 drivers/staging/zsmalloc/Makefile
rename {drivers/staging/zsmalloc => include/linux}/zsmalloc.h (100%)
rename drivers/staging/zsmalloc/zsmalloc-main.c => lib/zsmalloc.c (99%)
create mode 100644 mm/zswap.c
--
1.7.9.5
^ permalink raw reply [flat|nested] 38+ messages in thread
* [PATCHv3 0/6] zswap: compressed swap caching
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
Changelog:
v3:
* Dropped the zsmalloc patches from the set, except the promotion patch
which has be converted to a rename patch (vs full diff). The dropped
patches have been Acked and are going into Greg's staging tree soon.
* Separated [PATCHv2 7/9] into two patches since it makes changes for two
different reasons (Minchan)
* Moved ZSWAP_MAX_OUTSTANDING_FLUSHES near the top in zswap.c (Rik)
* Rebase to v3.8-rc5. linux-next is a little volatile with the
swapper_space per type changes which will effect this patchset.
* TODO: Move some stats from debugfs to sysfs. Which ones? (Rik)
v2:
* Rename zswap_fs_* functions to zswap_frontswap_* to avoid
confusion with "filesystem"
* Add comment about what the tree lock protects
* Remove "#if 0" code (should have been done before)
* Break out changes to existing swap code into separate patch
* Fix blank line EOF warning on documentation file
* Rebase to next-20130107
Zswap Overview:
Zswap is a lightweight compressed cache for swap pages. It takes
pages that are in the process of being swapped out and attempts to
compress them into a dynamically allocated RAM-based memory pool.
If this process is successful, the writeback to the swap device is
deferred and, in many cases, avoided completely. This results in
a significant I/O reduction and performance gains for systems that
are swapping.
The results of a kernel building benchmark indicate a
runtime reduction of 53% and an I/O reduction 76% with zswap vs normal
swapping with a kernel build under heavy memory pressure (see
Performance section for more).
Some addition performance metrics regarding the performance
improvements and I/O reductions that can be achieved using zswap as
measured by SPECjbb are provided here:
http://ibm.co/VCgHvM
These results include runs on x86 and new results on Power7+ with
hardware compression acceleration.
Of particular note is that zswap is able to evict pages from the compressed
cache, on an LRU basis, to the backing swap device when the compressed pool
reaches it size limit or the pool is unable to obtain additional pages
from the buddy allocator. This eviction functionality had been identified
as a requirement in prior community discussions.
Patchset Structure:
1: add atomic_t get/set to debugfs
2: promote zsmalloc to /lib
3,4: changes to existing swap code for zswap
5,6: add zswap and documentation
Rationale:
Zswap provides compressed swap caching that basically trades CPU cycles
for reduced swap I/O. This trade-off can result in a significant
performance improvement as reads to/writes from to the compressed
cache almost always faster that reading from a swap device
which incurs the latency of an asynchronous block I/O read.
Some potential benefits:
* Desktop/laptop users with limited RAM capacities can mitigate the
performance impact of swapping.
* Overcommitted guests that share a common I/O resource can
dramatically reduce their swap I/O pressure, avoiding heavy
handed I/O throttling by the hypervisor. This allows more work
to get done with less impact to the guest workload and guests
sharing the I/O subsystem
* Users with SSDs as swap devices can extend the life of the device by
drastically reducing life-shortening writes.
Compressed swap is also provided in zcache, along with page cache
compression and RAM clustering through RAMSter. Zswap seeks to deliver
the benefit of swap compression to users in a discrete function.
This design decision is akin to Unix design philosophy of doing one
thing well, it leaves file cache compression and other features
for separate code.
Design:
Zswap receives pages for compression through the Frontswap API and
is able to evict pages from its own compressed pool on an LRU basis
and write them back to the backing swap device in the case that the
compressed pool is full or unable to secure additional pages from
the buddy allocator.
Zswap makes use of zsmalloc for the managing the compressed memory
pool. This is because zsmalloc is specifically designed to minimize
fragmentation on large (> PAGE_SIZE/2) allocation sizes. Each
allocation in zsmalloc is not directly accessible by address.
Rather, a handle is return by the allocation routine and that handle
must be mapped before being accessed. The compressed memory pool grows
on demand and shrinks as compressed pages are freed. The pool is
not preallocated.
When a swap page is passed from frontswap to zswap, zswap maintains
a mapping of the swap entry, a combination of the swap type and swap
offset, to the zsmalloc handle that references that compressed swap
page. This mapping is achieved with a red-black tree per swap type.
The swap offset is the search key for the tree nodes.
Zswap seeks to be simple in its policies. Sysfs attributes allow for
two user controlled policies:
* max_compression_ratio - Maximum compression ratio, as as percentage,
for an acceptable compressed page. Any page that does not compress
by at least this ratio will be rejected.
* max_pool_percent - The maximum percentage of memory that the compressed
pool can occupy.
To enabled zswap, the "enabled" attribute must be set to 1 at boot time.
Zswap allows the compressor to be selected at kernel boot time by
setting the a??compressora?? attribute. The default compressor is lzo.
A debugfs interface is provided for various statistic about pool size,
number of pages stored, and various counters for the reasons pages
are rejected.
Performance, Kernel Building:
Setup
========
Gentoo w/ kernel v3.7-rc7
Quad-core i5-2500 @ 3.3GHz
512MB DDR3 1600MHz (limited with mem=512m on boot)
Filesystem and swap on 80GB HDD (about 58MB/s with hdparm -t)
majflt are major page faults reported by the time command
pswpin/out is the delta of pswpin/out from /proc/vmstat before and after
the make -jN
Summary
========
* Zswap reduces I/O and improves performance at all swap pressure levels.
* Under heavy swaping at 24 threads, zswap reduced I/O by 76%, saving
over 1.5GB of I/O, and cut runtime in half.
Details
========
I/O (in pages)
base zswap change change
N pswpin pswpout majflt I/O sum pswpin pswpout majflt I/O sum %I/O MB
8 1 335 291 627 0 0 249 249 -60% 1
12 3688 14315 5290 23293 123 860 5954 6937 -70% 64
16 12711 46179 16803 75693 2936 7390 46092 56418 -25% 75
20 42178 133781 49898 225857 9460 28382 92951 130793 -42% 371
24 96079 357280 105242 558601 7719 18484 109309 135512 -76% 1653
Runtime (in seconds)
N base zswap %change
8 107 107 0%
12 128 110 -14%
16 191 179 -6%
20 371 240 -35%
24 570 267 -53%
%CPU utilization (out of 400% on 4 cpus)
N base zswap %change
8 317 319 1%
12 267 311 16%
16 179 191 7%
20 94 143 52%
24 60 128 113%
Seth Jennings (6):
debugfs: add get/set for atomic types
zsmalloc: promote to lib/
mm: break up swap_writepage() for frontswap backends
mm: allow for outstanding swap writeback accounting
zswap: add to mm/
zswap: add documentation
Documentation/vm/zswap.txt | 73 ++
drivers/staging/Kconfig | 2 -
drivers/staging/Makefile | 1 -
drivers/staging/zcache/zcache-main.c | 3 +-
drivers/staging/zram/zram_drv.h | 3 +-
drivers/staging/zsmalloc/Kconfig | 10 -
drivers/staging/zsmalloc/Makefile | 3 -
fs/debugfs/file.c | 42 +
include/linux/debugfs.h | 2 +
include/linux/swap.h | 4 +
.../staging/zsmalloc => include/linux}/zsmalloc.h | 0
lib/Kconfig | 18 +
lib/Makefile | 1 +
.../zsmalloc/zsmalloc-main.c => lib/zsmalloc.c | 3 +-
mm/Kconfig | 15 +
mm/Makefile | 1 +
mm/page_io.c | 22 +-
mm/swap_state.c | 2 +-
mm/zswap.c | 1073 ++++++++++++++++++++
19 files changed, 1250 insertions(+), 28 deletions(-)
create mode 100644 Documentation/vm/zswap.txt
delete mode 100644 drivers/staging/zsmalloc/Kconfig
delete mode 100644 drivers/staging/zsmalloc/Makefile
rename {drivers/staging/zsmalloc => include/linux}/zsmalloc.h (100%)
rename drivers/staging/zsmalloc/zsmalloc-main.c => lib/zsmalloc.c (99%)
create mode 100644 mm/zswap.c
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
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^ permalink raw reply [flat|nested] 38+ messages in thread
* [PATCHv3 1/6] debugfs: add get/set for atomic types
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 21:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
debugfs currently lack the ability to create attributes
that set/get atomic_t values.
This patch adds support for this through a new
debugfs_create_atomic_t() function.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/debugfs/file.c | 42 ++++++++++++++++++++++++++++++++++++++++++
include/linux/debugfs.h | 2 ++
2 files changed, 44 insertions(+)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index c5ca6ae..fa26d5b 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -21,6 +21,7 @@
#include <linux/debugfs.h>
#include <linux/io.h>
#include <linux/slab.h>
+#include <linux/atomic.h>
static ssize_t default_read_file(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
@@ -403,6 +404,47 @@ struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
}
EXPORT_SYMBOL_GPL(debugfs_create_size_t);
+static int debugfs_atomic_t_set(void *data, u64 val)
+{
+ atomic_set((atomic_t *)data, val);
+ return 0;
+}
+static int debugfs_atomic_t_get(void *data, u64 *val)
+{
+ *val = atomic_read((atomic_t *)data);
+ return 0;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
+ debugfs_atomic_t_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set, "%llu\n");
+
+/**
+ * debugfs_create_atomic_t - create a debugfs file that is used to read and
+ * write an atomic_t value
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have
+ * @parent: a pointer to the parent dentry for this file. This should be a
+ * directory dentry if set. If this parameter is %NULL, then the
+ * file will be created in the root of the debugfs filesystem.
+ * @value: a pointer to the variable that the file should read to and write
+ * from.
+ */
+struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
+ struct dentry *parent, atomic_t *value)
+{
+ /* if there are no write bits set, make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value,
+ &fops_atomic_t_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value,
+ &fops_atomic_t_wo);
+
+ return debugfs_create_file(name, mode, parent, value, &fops_atomic_t);
+}
+EXPORT_SYMBOL_GPL(debugfs_create_atomic_t);
static ssize_t read_file_bool(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 66c434f..51fea70 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -79,6 +79,8 @@ struct dentry *debugfs_create_x64(const char *name, umode_t mode,
struct dentry *parent, u64 *value);
struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
struct dentry *parent, size_t *value);
+struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
+ struct dentry *parent, atomic_t *value);
struct dentry *debugfs_create_bool(const char *name, umode_t mode,
struct dentry *parent, u32 *value);
--
1.7.9.5
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 1/6] debugfs: add get/set for atomic types
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
debugfs currently lack the ability to create attributes
that set/get atomic_t values.
This patch adds support for this through a new
debugfs_create_atomic_t() function.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/debugfs/file.c | 42 ++++++++++++++++++++++++++++++++++++++++++
include/linux/debugfs.h | 2 ++
2 files changed, 44 insertions(+)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index c5ca6ae..fa26d5b 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -21,6 +21,7 @@
#include <linux/debugfs.h>
#include <linux/io.h>
#include <linux/slab.h>
+#include <linux/atomic.h>
static ssize_t default_read_file(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
@@ -403,6 +404,47 @@ struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
}
EXPORT_SYMBOL_GPL(debugfs_create_size_t);
+static int debugfs_atomic_t_set(void *data, u64 val)
+{
+ atomic_set((atomic_t *)data, val);
+ return 0;
+}
+static int debugfs_atomic_t_get(void *data, u64 *val)
+{
+ *val = atomic_read((atomic_t *)data);
+ return 0;
+}
+DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
+ debugfs_atomic_t_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set, "%llu\n");
+
+/**
+ * debugfs_create_atomic_t - create a debugfs file that is used to read and
+ * write an atomic_t value
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have
+ * @parent: a pointer to the parent dentry for this file. This should be a
+ * directory dentry if set. If this parameter is %NULL, then the
+ * file will be created in the root of the debugfs filesystem.
+ * @value: a pointer to the variable that the file should read to and write
+ * from.
+ */
+struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
+ struct dentry *parent, atomic_t *value)
+{
+ /* if there are no write bits set, make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value,
+ &fops_atomic_t_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value,
+ &fops_atomic_t_wo);
+
+ return debugfs_create_file(name, mode, parent, value, &fops_atomic_t);
+}
+EXPORT_SYMBOL_GPL(debugfs_create_atomic_t);
static ssize_t read_file_bool(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 66c434f..51fea70 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -79,6 +79,8 @@ struct dentry *debugfs_create_x64(const char *name, umode_t mode,
struct dentry *parent, u64 *value);
struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
struct dentry *parent, size_t *value);
+struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
+ struct dentry *parent, atomic_t *value);
struct dentry *debugfs_create_bool(const char *name, umode_t mode,
struct dentry *parent, u32 *value);
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 2/6] zsmalloc: promote to lib/
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 21:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
This patch promotes the slab-based zsmalloc memory allocator
from the staging tree to lib/
zswap depends on this allocator for storing compressed RAM pages
in an efficient way under system wide memory pressure where
high-order (greater than 0) page allocation are very likely to
fail.
For more information on zsmalloc and its internals, read the
documentation at the top of the zsmalloc.c file.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
--
This patch is similar to a patch Minchan has on out on the list
to promote for use in zram.
---
drivers/staging/Kconfig | 2 --
drivers/staging/Makefile | 1 -
drivers/staging/zcache/zcache-main.c | 3 +--
drivers/staging/zram/zram_drv.h | 3 +--
drivers/staging/zsmalloc/Kconfig | 10 ----------
drivers/staging/zsmalloc/Makefile | 3 ---
.../staging/zsmalloc => include/linux}/zsmalloc.h | 0
lib/Kconfig | 18 ++++++++++++++++++
lib/Makefile | 1 +
.../zsmalloc/zsmalloc-main.c => lib/zsmalloc.c | 3 +--
10 files changed, 22 insertions(+), 22 deletions(-)
delete mode 100644 drivers/staging/zsmalloc/Kconfig
delete mode 100644 drivers/staging/zsmalloc/Makefile
rename {drivers/staging/zsmalloc => include/linux}/zsmalloc.h (100%)
rename drivers/staging/zsmalloc/zsmalloc-main.c => lib/zsmalloc.c (99%)
diff --git a/drivers/staging/Kconfig b/drivers/staging/Kconfig
index 329bdb4..c0a7918 100644
--- a/drivers/staging/Kconfig
+++ b/drivers/staging/Kconfig
@@ -76,8 +76,6 @@ source "drivers/staging/zram/Kconfig"
source "drivers/staging/zcache/Kconfig"
-source "drivers/staging/zsmalloc/Kconfig"
-
source "drivers/staging/wlags49_h2/Kconfig"
source "drivers/staging/wlags49_h25/Kconfig"
diff --git a/drivers/staging/Makefile b/drivers/staging/Makefile
index c7ec486..1572fe5 100644
--- a/drivers/staging/Makefile
+++ b/drivers/staging/Makefile
@@ -32,7 +32,6 @@ obj-$(CONFIG_DX_SEP) += sep/
obj-$(CONFIG_IIO) += iio/
obj-$(CONFIG_ZRAM) += zram/
obj-$(CONFIG_ZCACHE) += zcache/
-obj-$(CONFIG_ZSMALLOC) += zsmalloc/
obj-$(CONFIG_WLAGS49_H2) += wlags49_h2/
obj-$(CONFIG_WLAGS49_H25) += wlags49_h25/
obj-$(CONFIG_FB_SM7XX) += sm7xxfb/
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 52b43b7..75c08c5 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -32,10 +32,9 @@
#include <linux/crypto.h>
#include <linux/string.h>
#include <linux/idr.h>
+#include <linux/zsmalloc.h>
#include "tmem.h"
-#include "../zsmalloc/zsmalloc.h"
-
#ifdef CONFIG_CLEANCACHE
#include <linux/cleancache.h>
#endif
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..1e72965 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -17,8 +17,7 @@
#include <linux/spinlock.h>
#include <linux/mutex.h>
-
-#include "../zsmalloc/zsmalloc.h"
+#include <linux/zsmalloc.h>
/*
* Some arbitrary value. This is just to catch
diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
deleted file mode 100644
index 9084565..0000000
--- a/drivers/staging/zsmalloc/Kconfig
+++ /dev/null
@@ -1,10 +0,0 @@
-config ZSMALLOC
- tristate "Memory allocator for compressed pages"
- default n
- help
- zsmalloc is a slab-based memory allocator designed to store
- compressed RAM pages. zsmalloc uses virtual memory mapping
- in order to reduce fragmentation. However, this results in a
- non-standard allocator interface where a handle, not a pointer, is
- returned by an alloc(). This handle must be mapped in order to
- access the allocated space.
diff --git a/drivers/staging/zsmalloc/Makefile b/drivers/staging/zsmalloc/Makefile
deleted file mode 100644
index b134848..0000000
--- a/drivers/staging/zsmalloc/Makefile
+++ /dev/null
@@ -1,3 +0,0 @@
-zsmalloc-y := zsmalloc-main.o
-
-obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
diff --git a/drivers/staging/zsmalloc/zsmalloc.h b/include/linux/zsmalloc.h
similarity index 100%
rename from drivers/staging/zsmalloc/zsmalloc.h
rename to include/linux/zsmalloc.h
diff --git a/lib/Kconfig b/lib/Kconfig
index 75cdb77..fdab273 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -219,6 +219,24 @@ config DECOMPRESS_LZO
config GENERIC_ALLOCATOR
boolean
+config ZSMALLOC
+ tristate "Memory allocator for compressed pages"
+ default n
+ help
+ zsmalloc is a slab-based memory allocator designed to store
+ compressed RAM pages. zsmalloc uses a memory pool that combines
+ single pages into higher order pages by linking them together
+ using the fields of the struct page. Allocations are then
+ mapped through copy buffers or VM mapping, in order to reduce
+ memory pool fragmentation and increase allocation success rate under
+ memory pressure.
+
+ This results in a non-standard allocator interface where
+ a handle, not a pointer, is returned by the allocation function.
+ This handle must be mapped in order to access the allocated space.
+
+ If unsure, say N.
+
#
# reed solomon support is select'ed if needed
#
diff --git a/lib/Makefile b/lib/Makefile
index 02ed6c0..70b0892 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -65,6 +65,7 @@ obj-$(CONFIG_CRC7) += crc7.o
obj-$(CONFIG_LIBCRC32C) += libcrc32c.o
obj-$(CONFIG_CRC8) += crc8.o
obj-$(CONFIG_GENERIC_ALLOCATOR) += genalloc.o
+obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate/
obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/
diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/lib/zsmalloc.c
similarity index 99%
rename from drivers/staging/zsmalloc/zsmalloc-main.c
rename to lib/zsmalloc.c
index 13018b7..d5146c7 100644
--- a/drivers/staging/zsmalloc/zsmalloc-main.c
+++ b/lib/zsmalloc.c
@@ -78,8 +78,7 @@
#include <linux/hardirq.h>
#include <linux/spinlock.h>
#include <linux/types.h>
-
-#include "zsmalloc.h"
+#include <linux/zsmalloc.h>
/*
* This must be power of 2 and greater than of equal to sizeof(link_free).
--
1.7.9.5
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 2/6] zsmalloc: promote to lib/
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
This patch promotes the slab-based zsmalloc memory allocator
from the staging tree to lib/
zswap depends on this allocator for storing compressed RAM pages
in an efficient way under system wide memory pressure where
high-order (greater than 0) page allocation are very likely to
fail.
For more information on zsmalloc and its internals, read the
documentation at the top of the zsmalloc.c file.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
--
This patch is similar to a patch Minchan has on out on the list
to promote for use in zram.
---
drivers/staging/Kconfig | 2 --
drivers/staging/Makefile | 1 -
drivers/staging/zcache/zcache-main.c | 3 +--
drivers/staging/zram/zram_drv.h | 3 +--
drivers/staging/zsmalloc/Kconfig | 10 ----------
drivers/staging/zsmalloc/Makefile | 3 ---
.../staging/zsmalloc => include/linux}/zsmalloc.h | 0
lib/Kconfig | 18 ++++++++++++++++++
lib/Makefile | 1 +
.../zsmalloc/zsmalloc-main.c => lib/zsmalloc.c | 3 +--
10 files changed, 22 insertions(+), 22 deletions(-)
delete mode 100644 drivers/staging/zsmalloc/Kconfig
delete mode 100644 drivers/staging/zsmalloc/Makefile
rename {drivers/staging/zsmalloc => include/linux}/zsmalloc.h (100%)
rename drivers/staging/zsmalloc/zsmalloc-main.c => lib/zsmalloc.c (99%)
diff --git a/drivers/staging/Kconfig b/drivers/staging/Kconfig
index 329bdb4..c0a7918 100644
--- a/drivers/staging/Kconfig
+++ b/drivers/staging/Kconfig
@@ -76,8 +76,6 @@ source "drivers/staging/zram/Kconfig"
source "drivers/staging/zcache/Kconfig"
-source "drivers/staging/zsmalloc/Kconfig"
-
source "drivers/staging/wlags49_h2/Kconfig"
source "drivers/staging/wlags49_h25/Kconfig"
diff --git a/drivers/staging/Makefile b/drivers/staging/Makefile
index c7ec486..1572fe5 100644
--- a/drivers/staging/Makefile
+++ b/drivers/staging/Makefile
@@ -32,7 +32,6 @@ obj-$(CONFIG_DX_SEP) += sep/
obj-$(CONFIG_IIO) += iio/
obj-$(CONFIG_ZRAM) += zram/
obj-$(CONFIG_ZCACHE) += zcache/
-obj-$(CONFIG_ZSMALLOC) += zsmalloc/
obj-$(CONFIG_WLAGS49_H2) += wlags49_h2/
obj-$(CONFIG_WLAGS49_H25) += wlags49_h25/
obj-$(CONFIG_FB_SM7XX) += sm7xxfb/
diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 52b43b7..75c08c5 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -32,10 +32,9 @@
#include <linux/crypto.h>
#include <linux/string.h>
#include <linux/idr.h>
+#include <linux/zsmalloc.h>
#include "tmem.h"
-#include "../zsmalloc/zsmalloc.h"
-
#ifdef CONFIG_CLEANCACHE
#include <linux/cleancache.h>
#endif
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..1e72965 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -17,8 +17,7 @@
#include <linux/spinlock.h>
#include <linux/mutex.h>
-
-#include "../zsmalloc/zsmalloc.h"
+#include <linux/zsmalloc.h>
/*
* Some arbitrary value. This is just to catch
diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
deleted file mode 100644
index 9084565..0000000
--- a/drivers/staging/zsmalloc/Kconfig
+++ /dev/null
@@ -1,10 +0,0 @@
-config ZSMALLOC
- tristate "Memory allocator for compressed pages"
- default n
- help
- zsmalloc is a slab-based memory allocator designed to store
- compressed RAM pages. zsmalloc uses virtual memory mapping
- in order to reduce fragmentation. However, this results in a
- non-standard allocator interface where a handle, not a pointer, is
- returned by an alloc(). This handle must be mapped in order to
- access the allocated space.
diff --git a/drivers/staging/zsmalloc/Makefile b/drivers/staging/zsmalloc/Makefile
deleted file mode 100644
index b134848..0000000
--- a/drivers/staging/zsmalloc/Makefile
+++ /dev/null
@@ -1,3 +0,0 @@
-zsmalloc-y := zsmalloc-main.o
-
-obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
diff --git a/drivers/staging/zsmalloc/zsmalloc.h b/include/linux/zsmalloc.h
similarity index 100%
rename from drivers/staging/zsmalloc/zsmalloc.h
rename to include/linux/zsmalloc.h
diff --git a/lib/Kconfig b/lib/Kconfig
index 75cdb77..fdab273 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -219,6 +219,24 @@ config DECOMPRESS_LZO
config GENERIC_ALLOCATOR
boolean
+config ZSMALLOC
+ tristate "Memory allocator for compressed pages"
+ default n
+ help
+ zsmalloc is a slab-based memory allocator designed to store
+ compressed RAM pages. zsmalloc uses a memory pool that combines
+ single pages into higher order pages by linking them together
+ using the fields of the struct page. Allocations are then
+ mapped through copy buffers or VM mapping, in order to reduce
+ memory pool fragmentation and increase allocation success rate under
+ memory pressure.
+
+ This results in a non-standard allocator interface where
+ a handle, not a pointer, is returned by the allocation function.
+ This handle must be mapped in order to access the allocated space.
+
+ If unsure, say N.
+
#
# reed solomon support is select'ed if needed
#
diff --git a/lib/Makefile b/lib/Makefile
index 02ed6c0..70b0892 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -65,6 +65,7 @@ obj-$(CONFIG_CRC7) += crc7.o
obj-$(CONFIG_LIBCRC32C) += libcrc32c.o
obj-$(CONFIG_CRC8) += crc8.o
obj-$(CONFIG_GENERIC_ALLOCATOR) += genalloc.o
+obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate/
obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/
diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/lib/zsmalloc.c
similarity index 99%
rename from drivers/staging/zsmalloc/zsmalloc-main.c
rename to lib/zsmalloc.c
index 13018b7..d5146c7 100644
--- a/drivers/staging/zsmalloc/zsmalloc-main.c
+++ b/lib/zsmalloc.c
@@ -78,8 +78,7 @@
#include <linux/hardirq.h>
#include <linux/spinlock.h>
#include <linux/types.h>
-
-#include "zsmalloc.h"
+#include <linux/zsmalloc.h>
/*
* This must be power of 2 and greater than of equal to sizeof(link_free).
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
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^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 3/6] mm: break up swap_writepage() for frontswap backends
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 21:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
swap_writepage() is currently where frontswap hooks into the swap
write path to capture pages with the frontswap_store() function.
However, if a frontswap backend wants to "resume" the writeback of
a page to the swap device, it can't call swap_writepage() as
the page will simply reenter the backend.
This patch separates swap_writepage() into a top and bottom half, the
bottom half named __swap_writepage() to allow a frontswap backend,
like zswap, to resume writeback beyond the frontswap_store() hook.
__add_to_swap_cache() is also made non-static so that the page for
which writeback is to be resumed can be added to the swap cache.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
include/linux/swap.h | 2 ++
mm/page_io.c | 16 +++++++++++++---
mm/swap_state.c | 2 +-
3 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 68df9c1..fc8920d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -321,6 +321,7 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
/* linux/mm/page_io.c */
extern int swap_readpage(struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern int __swap_writepage(struct page *page, struct writeback_control *wbc);
extern int swap_set_page_dirty(struct page *page);
extern void end_swap_bio_read(struct bio *bio, int err);
@@ -335,6 +336,7 @@ extern struct address_space swapper_space;
extern void show_swap_cache_info(void);
extern int add_to_swap(struct page *);
extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
+extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
extern void __delete_from_swap_cache(struct page *);
extern void delete_from_swap_cache(struct page *);
extern void free_page_and_swap_cache(struct page *);
diff --git a/mm/page_io.c b/mm/page_io.c
index 78eee32..1cb382d 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -179,15 +179,15 @@ bad_bmap:
goto out;
}
+int __swap_writepage(struct page *page, struct writeback_control *wbc);
+
/*
* We may have stale swap cache pages in memory: notice
* them here and get rid of the unnecessary final write.
*/
int swap_writepage(struct page *page, struct writeback_control *wbc)
{
- struct bio *bio;
- int ret = 0, rw = WRITE;
- struct swap_info_struct *sis = page_swap_info(page);
+ int ret = 0;
if (try_to_free_swap(page)) {
unlock_page(page);
@@ -199,6 +199,16 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
end_page_writeback(page);
goto out;
}
+ ret = __swap_writepage(page, wbc);
+out:
+ return ret;
+}
+
+int __swap_writepage(struct page *page, struct writeback_control *wbc)
+{
+ struct bio *bio;
+ int ret = 0, rw = WRITE;
+ struct swap_info_struct *sis = page_swap_info(page);
if (sis->flags & SWP_FILE) {
struct kiocb kiocb;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 0cb36fb..7eded9c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -67,7 +67,7 @@ void show_swap_cache_info(void)
* __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
* but sets SwapCache flag and private instead of mapping and index.
*/
-static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
+int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
int error;
--
1.7.9.5
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 3/6] mm: break up swap_writepage() for frontswap backends
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
swap_writepage() is currently where frontswap hooks into the swap
write path to capture pages with the frontswap_store() function.
However, if a frontswap backend wants to "resume" the writeback of
a page to the swap device, it can't call swap_writepage() as
the page will simply reenter the backend.
This patch separates swap_writepage() into a top and bottom half, the
bottom half named __swap_writepage() to allow a frontswap backend,
like zswap, to resume writeback beyond the frontswap_store() hook.
__add_to_swap_cache() is also made non-static so that the page for
which writeback is to be resumed can be added to the swap cache.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
include/linux/swap.h | 2 ++
mm/page_io.c | 16 +++++++++++++---
mm/swap_state.c | 2 +-
3 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 68df9c1..fc8920d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -321,6 +321,7 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
/* linux/mm/page_io.c */
extern int swap_readpage(struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern int __swap_writepage(struct page *page, struct writeback_control *wbc);
extern int swap_set_page_dirty(struct page *page);
extern void end_swap_bio_read(struct bio *bio, int err);
@@ -335,6 +336,7 @@ extern struct address_space swapper_space;
extern void show_swap_cache_info(void);
extern int add_to_swap(struct page *);
extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
+extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
extern void __delete_from_swap_cache(struct page *);
extern void delete_from_swap_cache(struct page *);
extern void free_page_and_swap_cache(struct page *);
diff --git a/mm/page_io.c b/mm/page_io.c
index 78eee32..1cb382d 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -179,15 +179,15 @@ bad_bmap:
goto out;
}
+int __swap_writepage(struct page *page, struct writeback_control *wbc);
+
/*
* We may have stale swap cache pages in memory: notice
* them here and get rid of the unnecessary final write.
*/
int swap_writepage(struct page *page, struct writeback_control *wbc)
{
- struct bio *bio;
- int ret = 0, rw = WRITE;
- struct swap_info_struct *sis = page_swap_info(page);
+ int ret = 0;
if (try_to_free_swap(page)) {
unlock_page(page);
@@ -199,6 +199,16 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
end_page_writeback(page);
goto out;
}
+ ret = __swap_writepage(page, wbc);
+out:
+ return ret;
+}
+
+int __swap_writepage(struct page *page, struct writeback_control *wbc)
+{
+ struct bio *bio;
+ int ret = 0, rw = WRITE;
+ struct swap_info_struct *sis = page_swap_info(page);
if (sis->flags & SWP_FILE) {
struct kiocb kiocb;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 0cb36fb..7eded9c 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -67,7 +67,7 @@ void show_swap_cache_info(void)
* __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
* but sets SwapCache flag and private instead of mapping and index.
*/
-static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
+int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
int error;
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 4/6] mm: allow for outstanding swap writeback accounting
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 21:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
To prevent flooding the swap device with writebacks, frontswap
backends need to count and limit the number of outstanding
writebacks. The incrementing of the counter can be done before
the call to __swap_writepage(). However, the caller must receive
a notification when the writeback completes in order to decrement
the counter.
To achieve this functionality, this patch modifies
__swap_writepage() to take the bio completion callback function
as an argument.
end_swap_bio_write(), the normal bio completion function, is also
made non-static so that code doing the accounting can call it
after the accounting is done.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
include/linux/swap.h | 4 +++-
mm/page_io.c | 12 +++++++-----
2 files changed, 10 insertions(+), 6 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index fc8920d..98981f0 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -321,7 +321,9 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
/* linux/mm/page_io.c */
extern int swap_readpage(struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
-extern int __swap_writepage(struct page *page, struct writeback_control *wbc);
+extern void end_swap_bio_write(struct bio *bio, int err);
+extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ void (*end_write_func)(struct bio *, int));
extern int swap_set_page_dirty(struct page *page);
extern void end_swap_bio_read(struct bio *bio, int err);
diff --git a/mm/page_io.c b/mm/page_io.c
index 1cb382d..56276fe 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -42,7 +42,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
return bio;
}
-static void end_swap_bio_write(struct bio *bio, int err)
+void end_swap_bio_write(struct bio *bio, int err)
{
const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
struct page *page = bio->bi_io_vec[0].bv_page;
@@ -179,7 +179,8 @@ bad_bmap:
goto out;
}
-int __swap_writepage(struct page *page, struct writeback_control *wbc);
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ void (*end_write_func)(struct bio *, int));
/*
* We may have stale swap cache pages in memory: notice
@@ -199,12 +200,13 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
end_page_writeback(page);
goto out;
}
- ret = __swap_writepage(page, wbc);
+ ret = __swap_writepage(page, wbc, end_swap_bio_write);
out:
return ret;
}
-int __swap_writepage(struct page *page, struct writeback_control *wbc)
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ void (*end_write_func)(struct bio *, int))
{
struct bio *bio;
int ret = 0, rw = WRITE;
@@ -236,7 +238,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc)
return ret;
}
- bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
+ bio = get_swap_bio(GFP_NOIO, page, end_write_func);
if (bio == NULL) {
set_page_dirty(page);
unlock_page(page);
--
1.7.9.5
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 4/6] mm: allow for outstanding swap writeback accounting
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
To prevent flooding the swap device with writebacks, frontswap
backends need to count and limit the number of outstanding
writebacks. The incrementing of the counter can be done before
the call to __swap_writepage(). However, the caller must receive
a notification when the writeback completes in order to decrement
the counter.
To achieve this functionality, this patch modifies
__swap_writepage() to take the bio completion callback function
as an argument.
end_swap_bio_write(), the normal bio completion function, is also
made non-static so that code doing the accounting can call it
after the accounting is done.
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
include/linux/swap.h | 4 +++-
mm/page_io.c | 12 +++++++-----
2 files changed, 10 insertions(+), 6 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index fc8920d..98981f0 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -321,7 +321,9 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
/* linux/mm/page_io.c */
extern int swap_readpage(struct page *);
extern int swap_writepage(struct page *page, struct writeback_control *wbc);
-extern int __swap_writepage(struct page *page, struct writeback_control *wbc);
+extern void end_swap_bio_write(struct bio *bio, int err);
+extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ void (*end_write_func)(struct bio *, int));
extern int swap_set_page_dirty(struct page *page);
extern void end_swap_bio_read(struct bio *bio, int err);
diff --git a/mm/page_io.c b/mm/page_io.c
index 1cb382d..56276fe 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -42,7 +42,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
return bio;
}
-static void end_swap_bio_write(struct bio *bio, int err)
+void end_swap_bio_write(struct bio *bio, int err)
{
const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
struct page *page = bio->bi_io_vec[0].bv_page;
@@ -179,7 +179,8 @@ bad_bmap:
goto out;
}
-int __swap_writepage(struct page *page, struct writeback_control *wbc);
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ void (*end_write_func)(struct bio *, int));
/*
* We may have stale swap cache pages in memory: notice
@@ -199,12 +200,13 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
end_page_writeback(page);
goto out;
}
- ret = __swap_writepage(page, wbc);
+ ret = __swap_writepage(page, wbc, end_swap_bio_write);
out:
return ret;
}
-int __swap_writepage(struct page *page, struct writeback_control *wbc)
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ void (*end_write_func)(struct bio *, int))
{
struct bio *bio;
int ret = 0, rw = WRITE;
@@ -236,7 +238,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc)
return ret;
}
- bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
+ bio = get_swap_bio(GFP_NOIO, page, end_write_func);
if (bio == NULL) {
set_page_dirty(page);
unlock_page(page);
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
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^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 5/6] zswap: add to mm/
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 21:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
zswap is a thin compression backend for frontswap. It receives
pages from frontswap and attempts to store them in a compressed
memory pool, resulting in an effective partial memory reclaim and
dramatically reduced swap device I/O.
Additional, in most cases, pages can be retrieved from this
compressed store much more quickly than reading from tradition
swap devices resulting in faster performance for many workloads.
This patch adds the zswap driver to mm/
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
mm/Kconfig | 15 +
mm/Makefile | 1 +
mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 1089 insertions(+)
create mode 100644 mm/zswap.c
diff --git a/mm/Kconfig b/mm/Kconfig
index 278e3ab..14b9acb 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -446,3 +446,18 @@ config FRONTSWAP
and swap data is stored as normal on the matching swap device.
If unsure, say Y to enable frontswap.
+
+config ZSWAP
+ bool "In-kernel swap page compression"
+ depends on FRONTSWAP && CRYPTO
+ select CRYPTO_LZO
+ select ZSMALLOC
+ default n
+ help
+ Zswap is a backend for the frontswap mechanism in the VMM.
+ It receives pages from frontswap and attempts to store them
+ in a compressed memory pool, resulting in an effective
+ partial memory reclaim. In addition, pages and be retrieved
+ from this compressed store much faster than most tradition
+ swap devices resulting in reduced I/O and faster performance
+ for many workloads.
diff --git a/mm/Makefile b/mm/Makefile
index 3a46287..1b1ed5c 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
obj-$(CONFIG_BOUNCE) += bounce.o
obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
obj-$(CONFIG_FRONTSWAP) += frontswap.o
+obj-$(CONFIG_ZSWAP) += zswap.o
obj-$(CONFIG_HAS_DMA) += dmapool.o
obj-$(CONFIG_HUGETLBFS) += hugetlb.o
obj-$(CONFIG_NUMA) += mempolicy.o
diff --git a/mm/zswap.c b/mm/zswap.c
new file mode 100644
index 0000000..050b6db
--- /dev/null
+++ b/mm/zswap.c
@@ -0,0 +1,1073 @@
+/*
+ * zswap-drv.c - zswap driver file
+ *
+ * zswap is a backend for frontswap that takes pages that are in the
+ * process of being swapped out and attempts to compress them and store
+ * them in a RAM-based memory pool. This results in a significant I/O
+ * reduction on the real swap device and, in the case of a slow swap
+ * device, can also improve workload performance.
+ *
+ * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+*/
+
+#include <linux/module.h>
+#include <linux/cpu.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/atomic.h>
+#include <linux/frontswap.h>
+#include <linux/rbtree.h>
+#include <linux/swap.h>
+#include <linux/crypto.h>
+#include <linux/mempool.h>
+#include <linux/zsmalloc.h>
+
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
+#include <linux/swapops.h>
+#include <linux/writeback.h>
+#include <linux/pagemap.h>
+
+/*********************************
+* statistics
+**********************************/
+/* Number of memory pages used by the compressed pool */
+static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
+/* The number of compressed pages currently stored in zswap */
+static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
+/* The number of outstanding pages awaiting writeback */
+static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
+
+/*
+ * The statistics below are not protected from concurrent access for
+ * performance reasons so they may not be a 100% accurate. However,
+ * the do provide useful information on roughly how many times a
+ * certain event is occurring.
+*/
+static u64 zswap_flushed_pages;
+static u64 zswap_reject_compress_poor;
+static u64 zswap_flush_attempted;
+static u64 zswap_reject_tmppage_fail;
+static u64 zswap_reject_flush_fail;
+static u64 zswap_reject_zsmalloc_fail;
+static u64 zswap_reject_kmemcache_fail;
+static u64 zswap_saved_by_flush;
+static u64 zswap_duplicate_entry;
+
+/*********************************
+* tunables
+**********************************/
+/* Enable/disable zswap (enabled by default, fixed at boot for now) */
+static bool zswap_enabled;
+module_param_named(enabled, zswap_enabled, bool, 0);
+
+/* Compressor to be used by zswap (fixed at boot for now) */
+#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
+static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
+module_param_named(compressor, zswap_compressor, charp, 0);
+
+/* The maximum percentage of memory that the compressed pool can occupy */
+static unsigned int zswap_max_pool_percent = 20;
+module_param_named(max_pool_percent,
+ zswap_max_pool_percent, uint, 0644);
+
+/*
+ * Maximum compression ratio, as as percentage, for an acceptable
+ * compressed page. Any pages that do not compress by at least
+ * this ratio will be rejected.
+*/
+static unsigned int zswap_max_compression_ratio = 80;
+module_param_named(max_compression_ratio,
+ zswap_max_compression_ratio, uint, 0644);
+
+/*
+ * Maximum number of outstanding flushes allowed at any given time.
+ * This is to prevent decompressing an unbounded number of compressed
+ * pages into the swap cache all at once, and to help with writeback
+ * congestion.
+*/
+#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
+
+/*********************************
+* compression functions
+**********************************/
+/* per-cpu compression transforms */
+static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
+
+enum comp_op {
+ ZSWAP_COMPOP_COMPRESS,
+ ZSWAP_COMPOP_DECOMPRESS
+};
+
+static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int *dlen)
+{
+ struct crypto_comp *tfm;
+ int ret;
+
+ tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
+ switch (op) {
+ case ZSWAP_COMPOP_COMPRESS:
+ ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
+ break;
+ case ZSWAP_COMPOP_DECOMPRESS:
+ ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ put_cpu();
+ return ret;
+}
+
+static int __init zswap_comp_init(void)
+{
+ if (!crypto_has_comp(zswap_compressor, 0, 0)) {
+ pr_info("zswap: %s compressor not available\n",
+ zswap_compressor);
+ /* fall back to default compressor */
+ zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
+ if (!crypto_has_comp(zswap_compressor, 0, 0))
+ /* can't even load the default compressor */
+ return -ENODEV;
+ }
+ pr_info("zswap: using %s compressor\n", zswap_compressor);
+
+ /* alloc percpu transforms */
+ zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
+ if (!zswap_comp_pcpu_tfms)
+ return -ENOMEM;
+ return 0;
+}
+
+static void zswap_comp_exit(void)
+{
+ /* free percpu transforms */
+ if (zswap_comp_pcpu_tfms)
+ free_percpu(zswap_comp_pcpu_tfms);
+}
+
+/*********************************
+* data structures
+**********************************/
+struct zswap_entry {
+ struct rb_node rbnode;
+ struct list_head lru;
+ int refcount;
+ unsigned type;
+ pgoff_t offset;
+ unsigned long handle;
+ unsigned int length;
+};
+
+/*
+ * The tree lock in the zswap_tree struct protects a few things:
+ * - the rbtree
+ * - the lru list
+ * - the refcount field of each entry in the tree
+ */
+struct zswap_tree {
+ struct rb_root rbroot;
+ struct list_head lru;
+ spinlock_t lock;
+ struct zs_pool *pool;
+};
+
+static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
+
+/*********************************
+* zswap entry functions
+**********************************/
+#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
+static struct kmem_cache *zswap_entry_cache;
+
+static inline int zswap_entry_cache_create(void)
+{
+ zswap_entry_cache =
+ kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
+ sizeof(struct zswap_entry), 0, 0, NULL);
+ return (zswap_entry_cache == NULL);
+}
+
+static inline void zswap_entry_cache_destory(void)
+{
+ kmem_cache_destroy(zswap_entry_cache);
+}
+
+static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
+{
+ struct zswap_entry *entry;
+ entry = kmem_cache_alloc(zswap_entry_cache, gfp);
+ if (!entry)
+ return NULL;
+ INIT_LIST_HEAD(&entry->lru);
+ entry->refcount = 1;
+ return entry;
+}
+
+static inline void zswap_entry_cache_free(struct zswap_entry *entry)
+{
+ kmem_cache_free(zswap_entry_cache, entry);
+}
+
+static inline void zswap_entry_get(struct zswap_entry *entry)
+{
+ entry->refcount++;
+}
+
+static inline int zswap_entry_put(struct zswap_entry *entry)
+{
+ entry->refcount--;
+ return entry->refcount;
+}
+
+/*********************************
+* rbtree functions
+**********************************/
+static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
+{
+ struct rb_node *node = root->rb_node;
+ struct zswap_entry *entry;
+
+ while (node) {
+ entry = rb_entry(node, struct zswap_entry, rbnode);
+ if (entry->offset > offset)
+ node = node->rb_left;
+ else if (entry->offset < offset)
+ node = node->rb_right;
+ else
+ return entry;
+ }
+ return NULL;
+}
+
+/*
+ * In the case that a entry with the same offset is found, it a pointer to
+ * the existing entry is stored in dupentry and the function returns -EEXIST
+*/
+static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
+ struct zswap_entry **dupentry)
+{
+ struct rb_node **link = &root->rb_node, *parent = NULL;
+ struct zswap_entry *myentry;
+
+ while (*link) {
+ parent = *link;
+ myentry = rb_entry(parent, struct zswap_entry, rbnode);
+ if (myentry->offset > entry->offset)
+ link = &(*link)->rb_left;
+ else if (myentry->offset < entry->offset)
+ link = &(*link)->rb_right;
+ else {
+ *dupentry = myentry;
+ return -EEXIST;
+ }
+ }
+ rb_link_node(&entry->rbnode, parent, link);
+ rb_insert_color(&entry->rbnode, root);
+ return 0;
+}
+
+/*********************************
+* per-cpu code
+**********************************/
+static DEFINE_PER_CPU(u8 *, zswap_dstmem);
+
+static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
+{
+ struct crypto_comp *tfm;
+ u8 *dst;
+
+ switch (action) {
+ case CPU_UP_PREPARE:
+ tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
+ if (IS_ERR(tfm)) {
+ pr_err("zswap: can't allocate compressor transform\n");
+ return NOTIFY_BAD;
+ }
+ *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
+ dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
+ if (!dst) {
+ pr_err("zswap: can't allocate compressor buffer\n");
+ crypto_free_comp(tfm);
+ *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
+ return NOTIFY_BAD;
+ }
+ per_cpu(zswap_dstmem, cpu) = dst;
+ break;
+ case CPU_DEAD:
+ case CPU_UP_CANCELED:
+ tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
+ if (tfm) {
+ crypto_free_comp(tfm);
+ *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
+ }
+ dst = per_cpu(zswap_dstmem, cpu);
+ if (dst) {
+ free_pages((unsigned long)dst, 1);
+ per_cpu(zswap_dstmem, cpu) = NULL;
+ }
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static int zswap_cpu_notifier(struct notifier_block *nb,
+ unsigned long action, void *pcpu)
+{
+ unsigned long cpu = (unsigned long)pcpu;
+ return __zswap_cpu_notifier(action, cpu);
+}
+
+static struct notifier_block zswap_cpu_notifier_block = {
+ .notifier_call = zswap_cpu_notifier
+};
+
+static int zswap_cpu_init(void)
+{
+ unsigned long cpu;
+
+ get_online_cpus();
+ for_each_online_cpu(cpu)
+ if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
+ goto cleanup;
+ register_cpu_notifier(&zswap_cpu_notifier_block);
+ put_online_cpus();
+ return 0;
+
+cleanup:
+ for_each_online_cpu(cpu)
+ __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
+ put_online_cpus();
+ return -ENOMEM;
+}
+
+/*********************************
+* zsmalloc callbacks
+**********************************/
+static mempool_t *zswap_page_pool;
+
+static u64 zswap_pool_limit_hit;
+
+static inline unsigned int zswap_max_pool_pages(void)
+{
+ return zswap_max_pool_percent * totalram_pages / 100;
+}
+
+static inline int zswap_page_pool_create(void)
+{
+ zswap_page_pool = mempool_create_page_pool(256, 0);
+ if (!zswap_page_pool)
+ return -ENOMEM;
+ return 0;
+}
+
+static inline void zswap_page_pool_destroy(void)
+{
+ mempool_destroy(zswap_page_pool);
+}
+
+static struct page *zswap_alloc_page(gfp_t flags)
+{
+ struct page *page;
+
+ if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
+ zswap_pool_limit_hit++;
+ return NULL;
+ }
+ page = mempool_alloc(zswap_page_pool, flags);
+ if (page)
+ atomic_inc(&zswap_pool_pages);
+ return page;
+}
+
+static void zswap_free_page(struct page *page)
+{
+ mempool_free(page, zswap_page_pool);
+ atomic_dec(&zswap_pool_pages);
+}
+
+static struct zs_ops zswap_zs_ops = {
+ .alloc = zswap_alloc_page,
+ .free = zswap_free_page
+};
+
+/*********************************
+* flush code
+**********************************/
+static void zswap_end_swap_write(struct bio *bio, int err)
+{
+ end_swap_bio_write(bio, err);
+ atomic_dec(&zswap_outstanding_flushes);
+ zswap_flushed_pages++;
+}
+
+/*
+ * zswap_get_swap_cache_page
+ *
+ * This is an adaption of read_swap_cache_async()
+ *
+ * If success, page is returned in retpage
+ * Returns 0 if page was already in the swap cache, page is not locked
+ * Returns 1 if the new page needs to be populated, page is locked
+ */
+static int zswap_get_swap_cache_page(swp_entry_t entry,
+ struct page **retpage)
+{
+ struct page *found_page, *new_page = NULL;
+ int err;
+
+ *retpage = NULL;
+ do {
+ /*
+ * First check the swap cache. Since this is normally
+ * called after lookup_swap_cache() failed, re-calling
+ * that would confuse statistics.
+ */
+ found_page = find_get_page(&swapper_space, entry.val);
+ if (found_page)
+ break;
+
+ /*
+ * Get a new page to read into from swap.
+ */
+ if (!new_page) {
+ new_page = alloc_page(GFP_KERNEL);
+ if (!new_page)
+ break; /* Out of memory */
+ }
+
+ /*
+ * call radix_tree_preload() while we can wait.
+ */
+ err = radix_tree_preload(GFP_KERNEL);
+ if (err)
+ break;
+
+ /*
+ * Swap entry may have been freed since our caller observed it.
+ */
+ err = swapcache_prepare(entry);
+ if (err == -EEXIST) { /* seems racy */
+ radix_tree_preload_end();
+ continue;
+ }
+ if (err) { /* swp entry is obsolete ? */
+ radix_tree_preload_end();
+ break;
+ }
+
+ /* May fail (-ENOMEM) if radix-tree node allocation failed. */
+ __set_page_locked(new_page);
+ SetPageSwapBacked(new_page);
+ err = __add_to_swap_cache(new_page, entry);
+ if (likely(!err)) {
+ radix_tree_preload_end();
+ lru_cache_add_anon(new_page);
+ *retpage = new_page;
+ return 1;
+ }
+ radix_tree_preload_end();
+ ClearPageSwapBacked(new_page);
+ __clear_page_locked(new_page);
+ /*
+ * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+ * clear SWAP_HAS_CACHE flag.
+ */
+ swapcache_free(entry, NULL);
+ } while (err != -ENOMEM);
+
+ if (new_page)
+ page_cache_release(new_page);
+ if (!found_page)
+ return -ENOMEM;
+ *retpage = found_page;
+ return 0;
+}
+
+static int zswap_flush_entry(struct zswap_entry *entry)
+{
+ unsigned long type = entry->type;
+ struct zswap_tree *tree = zswap_trees[type];
+ struct page *page;
+ swp_entry_t swpentry;
+ u8 *src, *dst;
+ unsigned int dlen;
+ int ret, refcount;
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ };
+
+ /* get/allocate page in the swap cache */
+ swpentry = swp_entry(type, entry->offset);
+ ret = zswap_get_swap_cache_page(swpentry, &page);
+ if (ret < 0)
+ return ret;
+ else if (ret) {
+ /* decompress */
+ dlen = PAGE_SIZE;
+ src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
+ dst = kmap_atomic(page);
+ ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
+ dst, &dlen);
+ kunmap_atomic(dst);
+ zs_unmap_object(tree->pool, entry->handle);
+ BUG_ON(ret);
+ BUG_ON(dlen != PAGE_SIZE);
+ SetPageUptodate(page);
+ } else {
+ /* page is already in the swap cache, ignore for now */
+ spin_lock(&tree->lock);
+ refcount = zswap_entry_put(entry);
+ spin_unlock(&tree->lock);
+
+ if (likely(refcount))
+ return 0;
+
+ /* if the refcount is zero, invalidate must have come in */
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+
+ return 0;
+ }
+
+ /* start writeback */
+ SetPageReclaim(page);
+ /*
+ * Return value is ignored here because it doesn't change anything
+ * for us. Page is returned unlocked.
+ */
+ (void)__swap_writepage(page, &wbc, zswap_end_swap_write);
+ page_cache_release(page);
+ atomic_inc(&zswap_outstanding_flushes);
+
+ /* remove */
+ spin_lock(&tree->lock);
+ refcount = zswap_entry_put(entry);
+ if (refcount > 1) {
+ /* load in progress, load will free */
+ spin_unlock(&tree->lock);
+ return 0;
+ }
+ if (refcount == 1)
+ /* no invalidate yet, remove from rbtree */
+ rb_erase(&entry->rbnode, &tree->rbroot);
+ spin_unlock(&tree->lock);
+
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+
+ return 0;
+}
+
+static void zswap_flush_entries(unsigned type, int nr)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry;
+ int i, ret;
+
+/*
+ * This limits is arbitrary for now until a better
+ * policy can be implemented. This is so we don't
+ * eat all of RAM decompressing pages for writeback.
+ */
+ if (atomic_read(&zswap_outstanding_flushes) >
+ ZSWAP_MAX_OUTSTANDING_FLUSHES)
+ return;
+
+ for (i = 0; i < nr; i++) {
+ /* dequeue from lru */
+ spin_lock(&tree->lock);
+ if (list_empty(&tree->lru)) {
+ spin_unlock(&tree->lock);
+ break;
+ }
+ entry = list_first_entry(&tree->lru,
+ struct zswap_entry, lru);
+ list_del(&entry->lru);
+ zswap_entry_get(entry);
+ spin_unlock(&tree->lock);
+ ret = zswap_flush_entry(entry);
+ if (ret) {
+ /* put back on the lru */
+ spin_lock(&tree->lock);
+ list_add(&entry->lru, &tree->lru);
+ spin_unlock(&tree->lock);
+ } else {
+ if (atomic_read(&zswap_outstanding_flushes) >
+ ZSWAP_MAX_OUTSTANDING_FLUSHES)
+ break;
+ }
+ }
+}
+
+/*******************************************
+* page pool for temporary compression result
+********************************************/
+#define ZSWAP_TMPPAGE_POOL_PAGES 16
+static LIST_HEAD(zswap_tmppage_list);
+static DEFINE_SPINLOCK(zswap_tmppage_lock);
+
+static void zswap_tmppage_pool_destroy(void)
+{
+ struct page *page, *tmppage;
+
+ spin_lock(&zswap_tmppage_lock);
+ list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
+ list_del(&page->lru);
+ __free_pages(page, 1);
+ }
+ spin_unlock(&zswap_tmppage_lock);
+}
+
+static int zswap_tmppage_pool_create(void)
+{
+ int i;
+ struct page *page;
+
+ for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
+ page = alloc_pages(GFP_KERNEL, 1);
+ if (!page) {
+ zswap_tmppage_pool_destroy();
+ return -ENOMEM;
+ }
+ spin_lock(&zswap_tmppage_lock);
+ list_add(&page->lru, &zswap_tmppage_list);
+ spin_unlock(&zswap_tmppage_lock);
+ }
+ return 0;
+}
+
+static inline struct page *zswap_tmppage_alloc(void)
+{
+ struct page *page;
+
+ spin_lock(&zswap_tmppage_lock);
+ if (list_empty(&zswap_tmppage_list)) {
+ spin_unlock(&zswap_tmppage_lock);
+ return NULL;
+ }
+ page = list_first_entry(&zswap_tmppage_list, struct page, lru);
+ list_del(&page->lru);
+ spin_unlock(&zswap_tmppage_lock);
+ return page;
+}
+
+static inline void zswap_tmppage_free(struct page *page)
+{
+ spin_lock(&zswap_tmppage_lock);
+ list_add(&page->lru, &zswap_tmppage_list);
+ spin_unlock(&zswap_tmppage_lock);
+}
+
+/*********************************
+* frontswap hooks
+**********************************/
+/* attempts to compress and store an single page */
+static int zswap_frontswap_store(unsigned type, pgoff_t offset, struct page *page)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry, *dupentry;
+ int ret;
+ unsigned int dlen = PAGE_SIZE;
+ unsigned long handle;
+ char *buf;
+ u8 *src, *dst, *tmpdst;
+ struct page *tmppage;
+ bool flush_attempted = 0;
+
+ if (!tree) {
+ ret = -ENODEV;
+ goto reject;
+ }
+
+ /* compress */
+ dst = get_cpu_var(zswap_dstmem);
+ src = kmap_atomic(page);
+ ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
+ kunmap_atomic(src);
+ if (ret) {
+ ret = -EINVAL;
+ goto freepage;
+ }
+ if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
+ zswap_reject_compress_poor++;
+ ret = -E2BIG;
+ goto freepage;
+ }
+
+ /* store */
+ handle = zs_malloc(tree->pool, dlen,
+ __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
+ __GFP_NOWARN);
+ if (!handle) {
+ zswap_flush_attempted++;
+ /*
+ * Copy compressed buffer out of per-cpu storage so
+ * we can re-enable preemption.
+ */
+ tmppage = zswap_tmppage_alloc();
+ if (!tmppage) {
+ zswap_reject_tmppage_fail++;
+ ret = -ENOMEM;
+ goto freepage;
+ }
+ flush_attempted = 1;
+ tmpdst = page_address(tmppage);
+ memcpy(tmpdst, dst, dlen);
+ dst = tmpdst;
+ put_cpu_var(zswap_dstmem);
+
+ /* try to free up some space */
+ /* TODO: replace with more targeted policy */
+ zswap_flush_entries(type, 16);
+ /* try again, allowing wait */
+ handle = zs_malloc(tree->pool, dlen,
+ __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
+ __GFP_NOWARN);
+ if (!handle) {
+ /* still no space, fail */
+ zswap_reject_zsmalloc_fail++;
+ ret = -ENOMEM;
+ goto freepage;
+ }
+ zswap_saved_by_flush++;
+ }
+
+ buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
+ memcpy(buf, dst, dlen);
+ zs_unmap_object(tree->pool, handle);
+ if (flush_attempted)
+ zswap_tmppage_free(tmppage);
+ else
+ put_cpu_var(zswap_dstmem);
+
+ /* allocate entry */
+ entry = zswap_entry_cache_alloc(GFP_KERNEL);
+ if (!entry) {
+ zswap_reject_kmemcache_fail++;
+ ret = -ENOMEM;
+ goto reject;
+ }
+
+ /* populate entry */
+ entry->type = type;
+ entry->offset = offset;
+ entry->handle = handle;
+ entry->length = dlen;
+
+ /* map */
+ spin_lock(&tree->lock);
+ do {
+ ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
+ if (ret == -EEXIST) {
+ zswap_duplicate_entry++;
+ /* remove from rbtree and lru */
+ rb_erase(&dupentry->rbnode, &tree->rbroot);
+ if (dupentry->lru.next != LIST_POISON1)
+ list_del(&dupentry->lru);
+ if (!zswap_entry_put(dupentry)) {
+ /* free */
+ zs_free(tree->pool, dupentry->handle);
+ zswap_entry_cache_free(dupentry);
+ atomic_dec(&zswap_stored_pages);
+ }
+ }
+ } while (ret == -EEXIST);
+ list_add_tail(&entry->lru, &tree->lru);
+ spin_unlock(&tree->lock);
+
+ /* update stats */
+ atomic_inc(&zswap_stored_pages);
+
+ return 0;
+
+freepage:
+ if (flush_attempted)
+ zswap_tmppage_free(tmppage);
+ else
+ put_cpu_var(zswap_dstmem);
+reject:
+ return ret;
+}
+
+/*
+ * returns 0 if the page was successfully decompressed
+ * return -1 on entry not found or error
+*/
+static int zswap_frontswap_load(unsigned type, pgoff_t offset, struct page *page)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry;
+ u8 *src, *dst;
+ unsigned int dlen;
+ int refcount;
+
+ /* find */
+ spin_lock(&tree->lock);
+ entry = zswap_rb_search(&tree->rbroot, offset);
+ if (!entry) {
+ /* entry was flushed */
+ spin_unlock(&tree->lock);
+ return -1;
+ }
+ zswap_entry_get(entry);
+
+ /* remove from lru */
+ if (entry->lru.next != LIST_POISON1)
+ list_del(&entry->lru);
+ spin_unlock(&tree->lock);
+
+ /* decompress */
+ dlen = PAGE_SIZE;
+ src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
+ dst = kmap_atomic(page);
+ zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
+ dst, &dlen);
+ kunmap_atomic(dst);
+ zs_unmap_object(tree->pool, entry->handle);
+
+ spin_lock(&tree->lock);
+ refcount = zswap_entry_put(entry);
+ if (likely(refcount)) {
+ list_add_tail(&entry->lru, &tree->lru);
+ spin_unlock(&tree->lock);
+ return 0;
+ }
+ spin_unlock(&tree->lock);
+
+ /*
+ * We don't have to unlink from the rbtree because zswap_flush_entry()
+ * or zswap_frontswap_invalidate page() has already done this for us if we
+ * are the last reference.
+ */
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+
+ return 0;
+}
+
+/* invalidates a single page */
+static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry;
+ int refcount;
+
+ if (!tree)
+ return;
+
+ /* find */
+ spin_lock(&tree->lock);
+ entry = zswap_rb_search(&tree->rbroot, offset);
+ if (!entry) {
+ /* entry was flushed */
+ spin_unlock(&tree->lock);
+ return;
+ }
+
+ /* remove from rbtree and lru */
+ rb_erase(&entry->rbnode, &tree->rbroot);
+ if (entry->lru.next != LIST_POISON1)
+ list_del(&entry->lru);
+ refcount = zswap_entry_put(entry);
+ spin_unlock(&tree->lock);
+ if (refcount) {
+ /* must be flushing */
+ return;
+ }
+
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+}
+
+/* invalidates all pages for the given swap type */
+static void zswap_frontswap_invalidate_area(unsigned type)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct rb_node *node, *next;
+ struct zswap_entry *entry;
+
+ if (!tree)
+ return;
+
+ /* walk the tree and free everything */
+ spin_lock(&tree->lock);
+ node = rb_first(&tree->rbroot);
+ while (node) {
+ entry = rb_entry(node, struct zswap_entry, rbnode);
+ zs_free(tree->pool, entry->handle);
+ next = rb_next(node);
+ zswap_entry_cache_free(entry);
+ node = next;
+ }
+ tree->rbroot = RB_ROOT;
+ INIT_LIST_HEAD(&tree->lru);
+ spin_unlock(&tree->lock);
+}
+
+/* NOTE: this is called in atomic context from swapon and must not sleep */
+static void zswap_frontswap_init(unsigned type)
+{
+ struct zswap_tree *tree;
+
+ tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
+ if (!tree)
+ goto err;
+ tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
+ if (!tree->pool)
+ goto freetree;
+ tree->rbroot = RB_ROOT;
+ INIT_LIST_HEAD(&tree->lru);
+ spin_lock_init(&tree->lock);
+ zswap_trees[type] = tree;
+ return;
+
+freetree:
+ kfree(tree);
+err:
+ pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
+}
+
+static struct frontswap_ops zswap_frontswap_ops = {
+ .store = zswap_frontswap_store,
+ .load = zswap_frontswap_load,
+ .invalidate_page = zswap_frontswap_invalidate_page,
+ .invalidate_area = zswap_frontswap_invalidate_area,
+ .init = zswap_frontswap_init
+};
+
+/*********************************
+* debugfs functions
+**********************************/
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+
+static struct dentry *zswap_debugfs_root;
+
+static int __init zswap_debugfs_init(void)
+{
+ if (!debugfs_initialized())
+ return -ENODEV;
+
+ zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
+ if (!zswap_debugfs_root)
+ return -ENOMEM;
+
+ debugfs_create_u64("saved_by_flush", S_IRUGO,
+ zswap_debugfs_root, &zswap_saved_by_flush);
+ debugfs_create_u64("pool_limit_hit", S_IRUGO,
+ zswap_debugfs_root, &zswap_pool_limit_hit);
+ debugfs_create_u64("reject_flush_attempted", S_IRUGO,
+ zswap_debugfs_root, &zswap_flush_attempted);
+ debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_tmppage_fail);
+ debugfs_create_u64("reject_flush_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_flush_fail);
+ debugfs_create_u64("reject_zsmalloc_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_zsmalloc_fail);
+ debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_kmemcache_fail);
+ debugfs_create_u64("reject_compress_poor", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_compress_poor);
+ debugfs_create_u64("flushed_pages", S_IRUGO,
+ zswap_debugfs_root, &zswap_flushed_pages);
+ debugfs_create_u64("duplicate_entry", S_IRUGO,
+ zswap_debugfs_root, &zswap_duplicate_entry);
+ debugfs_create_atomic_t("pool_pages", S_IRUGO,
+ zswap_debugfs_root, &zswap_pool_pages);
+ debugfs_create_atomic_t("stored_pages", S_IRUGO,
+ zswap_debugfs_root, &zswap_stored_pages);
+ debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
+ zswap_debugfs_root, &zswap_outstanding_flushes);
+
+ return 0;
+}
+
+static void __exit zswap_debugfs_exit(void)
+{
+ if (zswap_debugfs_root)
+ debugfs_remove_recursive(zswap_debugfs_root);
+}
+#else
+static inline int __init zswap_debugfs_init(void)
+{
+ return 0;
+}
+
+static inline void __exit zswap_debugfs_exit(void) { }
+#endif
+
+/*********************************
+* module init and exit
+**********************************/
+static int __init init_zswap(void)
+{
+ if (!zswap_enabled)
+ return 0;
+
+ pr_info("loading zswap\n");
+ if (zswap_entry_cache_create()) {
+ pr_err("zswap: entry cache creation failed\n");
+ goto error;
+ }
+ if (zswap_page_pool_create()) {
+ pr_err("zswap: page pool initialization failed\n");
+ goto pagepoolfail;
+ }
+ if (zswap_tmppage_pool_create()) {
+ pr_err("zswap: workmem pool initialization failed\n");
+ goto tmppoolfail;
+ }
+ if (zswap_comp_init()) {
+ pr_err("zswap: compressor initialization failed\n");
+ goto compfail;
+ }
+ if (zswap_cpu_init()) {
+ pr_err("zswap: per-cpu initialization failed\n");
+ goto pcpufail;
+ }
+ frontswap_register_ops(&zswap_frontswap_ops);
+ if (zswap_debugfs_init())
+ pr_warn("zswap: debugfs initialization failed\n");
+ return 0;
+pcpufail:
+ zswap_comp_exit();
+compfail:
+ zswap_tmppage_pool_destroy();
+tmppoolfail:
+ zswap_page_pool_destroy();
+pagepoolfail:
+ zswap_entry_cache_destory();
+error:
+ return -ENOMEM;
+}
+/* must be late so crypto has time to come up */
+late_initcall(init_zswap);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
+MODULE_DESCRIPTION("Compression backend for frontswap pages");
--
1.7.9.5
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 5/6] zswap: add to mm/
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
zswap is a thin compression backend for frontswap. It receives
pages from frontswap and attempts to store them in a compressed
memory pool, resulting in an effective partial memory reclaim and
dramatically reduced swap device I/O.
Additional, in most cases, pages can be retrieved from this
compressed store much more quickly than reading from tradition
swap devices resulting in faster performance for many workloads.
This patch adds the zswap driver to mm/
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
mm/Kconfig | 15 +
mm/Makefile | 1 +
mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 1089 insertions(+)
create mode 100644 mm/zswap.c
diff --git a/mm/Kconfig b/mm/Kconfig
index 278e3ab..14b9acb 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -446,3 +446,18 @@ config FRONTSWAP
and swap data is stored as normal on the matching swap device.
If unsure, say Y to enable frontswap.
+
+config ZSWAP
+ bool "In-kernel swap page compression"
+ depends on FRONTSWAP && CRYPTO
+ select CRYPTO_LZO
+ select ZSMALLOC
+ default n
+ help
+ Zswap is a backend for the frontswap mechanism in the VMM.
+ It receives pages from frontswap and attempts to store them
+ in a compressed memory pool, resulting in an effective
+ partial memory reclaim. In addition, pages and be retrieved
+ from this compressed store much faster than most tradition
+ swap devices resulting in reduced I/O and faster performance
+ for many workloads.
diff --git a/mm/Makefile b/mm/Makefile
index 3a46287..1b1ed5c 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
obj-$(CONFIG_BOUNCE) += bounce.o
obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
obj-$(CONFIG_FRONTSWAP) += frontswap.o
+obj-$(CONFIG_ZSWAP) += zswap.o
obj-$(CONFIG_HAS_DMA) += dmapool.o
obj-$(CONFIG_HUGETLBFS) += hugetlb.o
obj-$(CONFIG_NUMA) += mempolicy.o
diff --git a/mm/zswap.c b/mm/zswap.c
new file mode 100644
index 0000000..050b6db
--- /dev/null
+++ b/mm/zswap.c
@@ -0,0 +1,1073 @@
+/*
+ * zswap-drv.c - zswap driver file
+ *
+ * zswap is a backend for frontswap that takes pages that are in the
+ * process of being swapped out and attempts to compress them and store
+ * them in a RAM-based memory pool. This results in a significant I/O
+ * reduction on the real swap device and, in the case of a slow swap
+ * device, can also improve workload performance.
+ *
+ * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+*/
+
+#include <linux/module.h>
+#include <linux/cpu.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/atomic.h>
+#include <linux/frontswap.h>
+#include <linux/rbtree.h>
+#include <linux/swap.h>
+#include <linux/crypto.h>
+#include <linux/mempool.h>
+#include <linux/zsmalloc.h>
+
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
+#include <linux/swapops.h>
+#include <linux/writeback.h>
+#include <linux/pagemap.h>
+
+/*********************************
+* statistics
+**********************************/
+/* Number of memory pages used by the compressed pool */
+static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
+/* The number of compressed pages currently stored in zswap */
+static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
+/* The number of outstanding pages awaiting writeback */
+static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
+
+/*
+ * The statistics below are not protected from concurrent access for
+ * performance reasons so they may not be a 100% accurate. However,
+ * the do provide useful information on roughly how many times a
+ * certain event is occurring.
+*/
+static u64 zswap_flushed_pages;
+static u64 zswap_reject_compress_poor;
+static u64 zswap_flush_attempted;
+static u64 zswap_reject_tmppage_fail;
+static u64 zswap_reject_flush_fail;
+static u64 zswap_reject_zsmalloc_fail;
+static u64 zswap_reject_kmemcache_fail;
+static u64 zswap_saved_by_flush;
+static u64 zswap_duplicate_entry;
+
+/*********************************
+* tunables
+**********************************/
+/* Enable/disable zswap (enabled by default, fixed at boot for now) */
+static bool zswap_enabled;
+module_param_named(enabled, zswap_enabled, bool, 0);
+
+/* Compressor to be used by zswap (fixed at boot for now) */
+#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
+static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
+module_param_named(compressor, zswap_compressor, charp, 0);
+
+/* The maximum percentage of memory that the compressed pool can occupy */
+static unsigned int zswap_max_pool_percent = 20;
+module_param_named(max_pool_percent,
+ zswap_max_pool_percent, uint, 0644);
+
+/*
+ * Maximum compression ratio, as as percentage, for an acceptable
+ * compressed page. Any pages that do not compress by at least
+ * this ratio will be rejected.
+*/
+static unsigned int zswap_max_compression_ratio = 80;
+module_param_named(max_compression_ratio,
+ zswap_max_compression_ratio, uint, 0644);
+
+/*
+ * Maximum number of outstanding flushes allowed at any given time.
+ * This is to prevent decompressing an unbounded number of compressed
+ * pages into the swap cache all at once, and to help with writeback
+ * congestion.
+*/
+#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
+
+/*********************************
+* compression functions
+**********************************/
+/* per-cpu compression transforms */
+static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
+
+enum comp_op {
+ ZSWAP_COMPOP_COMPRESS,
+ ZSWAP_COMPOP_DECOMPRESS
+};
+
+static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int *dlen)
+{
+ struct crypto_comp *tfm;
+ int ret;
+
+ tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
+ switch (op) {
+ case ZSWAP_COMPOP_COMPRESS:
+ ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
+ break;
+ case ZSWAP_COMPOP_DECOMPRESS:
+ ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ put_cpu();
+ return ret;
+}
+
+static int __init zswap_comp_init(void)
+{
+ if (!crypto_has_comp(zswap_compressor, 0, 0)) {
+ pr_info("zswap: %s compressor not available\n",
+ zswap_compressor);
+ /* fall back to default compressor */
+ zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
+ if (!crypto_has_comp(zswap_compressor, 0, 0))
+ /* can't even load the default compressor */
+ return -ENODEV;
+ }
+ pr_info("zswap: using %s compressor\n", zswap_compressor);
+
+ /* alloc percpu transforms */
+ zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
+ if (!zswap_comp_pcpu_tfms)
+ return -ENOMEM;
+ return 0;
+}
+
+static void zswap_comp_exit(void)
+{
+ /* free percpu transforms */
+ if (zswap_comp_pcpu_tfms)
+ free_percpu(zswap_comp_pcpu_tfms);
+}
+
+/*********************************
+* data structures
+**********************************/
+struct zswap_entry {
+ struct rb_node rbnode;
+ struct list_head lru;
+ int refcount;
+ unsigned type;
+ pgoff_t offset;
+ unsigned long handle;
+ unsigned int length;
+};
+
+/*
+ * The tree lock in the zswap_tree struct protects a few things:
+ * - the rbtree
+ * - the lru list
+ * - the refcount field of each entry in the tree
+ */
+struct zswap_tree {
+ struct rb_root rbroot;
+ struct list_head lru;
+ spinlock_t lock;
+ struct zs_pool *pool;
+};
+
+static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
+
+/*********************************
+* zswap entry functions
+**********************************/
+#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
+static struct kmem_cache *zswap_entry_cache;
+
+static inline int zswap_entry_cache_create(void)
+{
+ zswap_entry_cache =
+ kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
+ sizeof(struct zswap_entry), 0, 0, NULL);
+ return (zswap_entry_cache == NULL);
+}
+
+static inline void zswap_entry_cache_destory(void)
+{
+ kmem_cache_destroy(zswap_entry_cache);
+}
+
+static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
+{
+ struct zswap_entry *entry;
+ entry = kmem_cache_alloc(zswap_entry_cache, gfp);
+ if (!entry)
+ return NULL;
+ INIT_LIST_HEAD(&entry->lru);
+ entry->refcount = 1;
+ return entry;
+}
+
+static inline void zswap_entry_cache_free(struct zswap_entry *entry)
+{
+ kmem_cache_free(zswap_entry_cache, entry);
+}
+
+static inline void zswap_entry_get(struct zswap_entry *entry)
+{
+ entry->refcount++;
+}
+
+static inline int zswap_entry_put(struct zswap_entry *entry)
+{
+ entry->refcount--;
+ return entry->refcount;
+}
+
+/*********************************
+* rbtree functions
+**********************************/
+static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
+{
+ struct rb_node *node = root->rb_node;
+ struct zswap_entry *entry;
+
+ while (node) {
+ entry = rb_entry(node, struct zswap_entry, rbnode);
+ if (entry->offset > offset)
+ node = node->rb_left;
+ else if (entry->offset < offset)
+ node = node->rb_right;
+ else
+ return entry;
+ }
+ return NULL;
+}
+
+/*
+ * In the case that a entry with the same offset is found, it a pointer to
+ * the existing entry is stored in dupentry and the function returns -EEXIST
+*/
+static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
+ struct zswap_entry **dupentry)
+{
+ struct rb_node **link = &root->rb_node, *parent = NULL;
+ struct zswap_entry *myentry;
+
+ while (*link) {
+ parent = *link;
+ myentry = rb_entry(parent, struct zswap_entry, rbnode);
+ if (myentry->offset > entry->offset)
+ link = &(*link)->rb_left;
+ else if (myentry->offset < entry->offset)
+ link = &(*link)->rb_right;
+ else {
+ *dupentry = myentry;
+ return -EEXIST;
+ }
+ }
+ rb_link_node(&entry->rbnode, parent, link);
+ rb_insert_color(&entry->rbnode, root);
+ return 0;
+}
+
+/*********************************
+* per-cpu code
+**********************************/
+static DEFINE_PER_CPU(u8 *, zswap_dstmem);
+
+static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
+{
+ struct crypto_comp *tfm;
+ u8 *dst;
+
+ switch (action) {
+ case CPU_UP_PREPARE:
+ tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
+ if (IS_ERR(tfm)) {
+ pr_err("zswap: can't allocate compressor transform\n");
+ return NOTIFY_BAD;
+ }
+ *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
+ dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
+ if (!dst) {
+ pr_err("zswap: can't allocate compressor buffer\n");
+ crypto_free_comp(tfm);
+ *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
+ return NOTIFY_BAD;
+ }
+ per_cpu(zswap_dstmem, cpu) = dst;
+ break;
+ case CPU_DEAD:
+ case CPU_UP_CANCELED:
+ tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
+ if (tfm) {
+ crypto_free_comp(tfm);
+ *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
+ }
+ dst = per_cpu(zswap_dstmem, cpu);
+ if (dst) {
+ free_pages((unsigned long)dst, 1);
+ per_cpu(zswap_dstmem, cpu) = NULL;
+ }
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static int zswap_cpu_notifier(struct notifier_block *nb,
+ unsigned long action, void *pcpu)
+{
+ unsigned long cpu = (unsigned long)pcpu;
+ return __zswap_cpu_notifier(action, cpu);
+}
+
+static struct notifier_block zswap_cpu_notifier_block = {
+ .notifier_call = zswap_cpu_notifier
+};
+
+static int zswap_cpu_init(void)
+{
+ unsigned long cpu;
+
+ get_online_cpus();
+ for_each_online_cpu(cpu)
+ if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
+ goto cleanup;
+ register_cpu_notifier(&zswap_cpu_notifier_block);
+ put_online_cpus();
+ return 0;
+
+cleanup:
+ for_each_online_cpu(cpu)
+ __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
+ put_online_cpus();
+ return -ENOMEM;
+}
+
+/*********************************
+* zsmalloc callbacks
+**********************************/
+static mempool_t *zswap_page_pool;
+
+static u64 zswap_pool_limit_hit;
+
+static inline unsigned int zswap_max_pool_pages(void)
+{
+ return zswap_max_pool_percent * totalram_pages / 100;
+}
+
+static inline int zswap_page_pool_create(void)
+{
+ zswap_page_pool = mempool_create_page_pool(256, 0);
+ if (!zswap_page_pool)
+ return -ENOMEM;
+ return 0;
+}
+
+static inline void zswap_page_pool_destroy(void)
+{
+ mempool_destroy(zswap_page_pool);
+}
+
+static struct page *zswap_alloc_page(gfp_t flags)
+{
+ struct page *page;
+
+ if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
+ zswap_pool_limit_hit++;
+ return NULL;
+ }
+ page = mempool_alloc(zswap_page_pool, flags);
+ if (page)
+ atomic_inc(&zswap_pool_pages);
+ return page;
+}
+
+static void zswap_free_page(struct page *page)
+{
+ mempool_free(page, zswap_page_pool);
+ atomic_dec(&zswap_pool_pages);
+}
+
+static struct zs_ops zswap_zs_ops = {
+ .alloc = zswap_alloc_page,
+ .free = zswap_free_page
+};
+
+/*********************************
+* flush code
+**********************************/
+static void zswap_end_swap_write(struct bio *bio, int err)
+{
+ end_swap_bio_write(bio, err);
+ atomic_dec(&zswap_outstanding_flushes);
+ zswap_flushed_pages++;
+}
+
+/*
+ * zswap_get_swap_cache_page
+ *
+ * This is an adaption of read_swap_cache_async()
+ *
+ * If success, page is returned in retpage
+ * Returns 0 if page was already in the swap cache, page is not locked
+ * Returns 1 if the new page needs to be populated, page is locked
+ */
+static int zswap_get_swap_cache_page(swp_entry_t entry,
+ struct page **retpage)
+{
+ struct page *found_page, *new_page = NULL;
+ int err;
+
+ *retpage = NULL;
+ do {
+ /*
+ * First check the swap cache. Since this is normally
+ * called after lookup_swap_cache() failed, re-calling
+ * that would confuse statistics.
+ */
+ found_page = find_get_page(&swapper_space, entry.val);
+ if (found_page)
+ break;
+
+ /*
+ * Get a new page to read into from swap.
+ */
+ if (!new_page) {
+ new_page = alloc_page(GFP_KERNEL);
+ if (!new_page)
+ break; /* Out of memory */
+ }
+
+ /*
+ * call radix_tree_preload() while we can wait.
+ */
+ err = radix_tree_preload(GFP_KERNEL);
+ if (err)
+ break;
+
+ /*
+ * Swap entry may have been freed since our caller observed it.
+ */
+ err = swapcache_prepare(entry);
+ if (err == -EEXIST) { /* seems racy */
+ radix_tree_preload_end();
+ continue;
+ }
+ if (err) { /* swp entry is obsolete ? */
+ radix_tree_preload_end();
+ break;
+ }
+
+ /* May fail (-ENOMEM) if radix-tree node allocation failed. */
+ __set_page_locked(new_page);
+ SetPageSwapBacked(new_page);
+ err = __add_to_swap_cache(new_page, entry);
+ if (likely(!err)) {
+ radix_tree_preload_end();
+ lru_cache_add_anon(new_page);
+ *retpage = new_page;
+ return 1;
+ }
+ radix_tree_preload_end();
+ ClearPageSwapBacked(new_page);
+ __clear_page_locked(new_page);
+ /*
+ * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+ * clear SWAP_HAS_CACHE flag.
+ */
+ swapcache_free(entry, NULL);
+ } while (err != -ENOMEM);
+
+ if (new_page)
+ page_cache_release(new_page);
+ if (!found_page)
+ return -ENOMEM;
+ *retpage = found_page;
+ return 0;
+}
+
+static int zswap_flush_entry(struct zswap_entry *entry)
+{
+ unsigned long type = entry->type;
+ struct zswap_tree *tree = zswap_trees[type];
+ struct page *page;
+ swp_entry_t swpentry;
+ u8 *src, *dst;
+ unsigned int dlen;
+ int ret, refcount;
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ };
+
+ /* get/allocate page in the swap cache */
+ swpentry = swp_entry(type, entry->offset);
+ ret = zswap_get_swap_cache_page(swpentry, &page);
+ if (ret < 0)
+ return ret;
+ else if (ret) {
+ /* decompress */
+ dlen = PAGE_SIZE;
+ src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
+ dst = kmap_atomic(page);
+ ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
+ dst, &dlen);
+ kunmap_atomic(dst);
+ zs_unmap_object(tree->pool, entry->handle);
+ BUG_ON(ret);
+ BUG_ON(dlen != PAGE_SIZE);
+ SetPageUptodate(page);
+ } else {
+ /* page is already in the swap cache, ignore for now */
+ spin_lock(&tree->lock);
+ refcount = zswap_entry_put(entry);
+ spin_unlock(&tree->lock);
+
+ if (likely(refcount))
+ return 0;
+
+ /* if the refcount is zero, invalidate must have come in */
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+
+ return 0;
+ }
+
+ /* start writeback */
+ SetPageReclaim(page);
+ /*
+ * Return value is ignored here because it doesn't change anything
+ * for us. Page is returned unlocked.
+ */
+ (void)__swap_writepage(page, &wbc, zswap_end_swap_write);
+ page_cache_release(page);
+ atomic_inc(&zswap_outstanding_flushes);
+
+ /* remove */
+ spin_lock(&tree->lock);
+ refcount = zswap_entry_put(entry);
+ if (refcount > 1) {
+ /* load in progress, load will free */
+ spin_unlock(&tree->lock);
+ return 0;
+ }
+ if (refcount == 1)
+ /* no invalidate yet, remove from rbtree */
+ rb_erase(&entry->rbnode, &tree->rbroot);
+ spin_unlock(&tree->lock);
+
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+
+ return 0;
+}
+
+static void zswap_flush_entries(unsigned type, int nr)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry;
+ int i, ret;
+
+/*
+ * This limits is arbitrary for now until a better
+ * policy can be implemented. This is so we don't
+ * eat all of RAM decompressing pages for writeback.
+ */
+ if (atomic_read(&zswap_outstanding_flushes) >
+ ZSWAP_MAX_OUTSTANDING_FLUSHES)
+ return;
+
+ for (i = 0; i < nr; i++) {
+ /* dequeue from lru */
+ spin_lock(&tree->lock);
+ if (list_empty(&tree->lru)) {
+ spin_unlock(&tree->lock);
+ break;
+ }
+ entry = list_first_entry(&tree->lru,
+ struct zswap_entry, lru);
+ list_del(&entry->lru);
+ zswap_entry_get(entry);
+ spin_unlock(&tree->lock);
+ ret = zswap_flush_entry(entry);
+ if (ret) {
+ /* put back on the lru */
+ spin_lock(&tree->lock);
+ list_add(&entry->lru, &tree->lru);
+ spin_unlock(&tree->lock);
+ } else {
+ if (atomic_read(&zswap_outstanding_flushes) >
+ ZSWAP_MAX_OUTSTANDING_FLUSHES)
+ break;
+ }
+ }
+}
+
+/*******************************************
+* page pool for temporary compression result
+********************************************/
+#define ZSWAP_TMPPAGE_POOL_PAGES 16
+static LIST_HEAD(zswap_tmppage_list);
+static DEFINE_SPINLOCK(zswap_tmppage_lock);
+
+static void zswap_tmppage_pool_destroy(void)
+{
+ struct page *page, *tmppage;
+
+ spin_lock(&zswap_tmppage_lock);
+ list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
+ list_del(&page->lru);
+ __free_pages(page, 1);
+ }
+ spin_unlock(&zswap_tmppage_lock);
+}
+
+static int zswap_tmppage_pool_create(void)
+{
+ int i;
+ struct page *page;
+
+ for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
+ page = alloc_pages(GFP_KERNEL, 1);
+ if (!page) {
+ zswap_tmppage_pool_destroy();
+ return -ENOMEM;
+ }
+ spin_lock(&zswap_tmppage_lock);
+ list_add(&page->lru, &zswap_tmppage_list);
+ spin_unlock(&zswap_tmppage_lock);
+ }
+ return 0;
+}
+
+static inline struct page *zswap_tmppage_alloc(void)
+{
+ struct page *page;
+
+ spin_lock(&zswap_tmppage_lock);
+ if (list_empty(&zswap_tmppage_list)) {
+ spin_unlock(&zswap_tmppage_lock);
+ return NULL;
+ }
+ page = list_first_entry(&zswap_tmppage_list, struct page, lru);
+ list_del(&page->lru);
+ spin_unlock(&zswap_tmppage_lock);
+ return page;
+}
+
+static inline void zswap_tmppage_free(struct page *page)
+{
+ spin_lock(&zswap_tmppage_lock);
+ list_add(&page->lru, &zswap_tmppage_list);
+ spin_unlock(&zswap_tmppage_lock);
+}
+
+/*********************************
+* frontswap hooks
+**********************************/
+/* attempts to compress and store an single page */
+static int zswap_frontswap_store(unsigned type, pgoff_t offset, struct page *page)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry, *dupentry;
+ int ret;
+ unsigned int dlen = PAGE_SIZE;
+ unsigned long handle;
+ char *buf;
+ u8 *src, *dst, *tmpdst;
+ struct page *tmppage;
+ bool flush_attempted = 0;
+
+ if (!tree) {
+ ret = -ENODEV;
+ goto reject;
+ }
+
+ /* compress */
+ dst = get_cpu_var(zswap_dstmem);
+ src = kmap_atomic(page);
+ ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
+ kunmap_atomic(src);
+ if (ret) {
+ ret = -EINVAL;
+ goto freepage;
+ }
+ if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
+ zswap_reject_compress_poor++;
+ ret = -E2BIG;
+ goto freepage;
+ }
+
+ /* store */
+ handle = zs_malloc(tree->pool, dlen,
+ __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
+ __GFP_NOWARN);
+ if (!handle) {
+ zswap_flush_attempted++;
+ /*
+ * Copy compressed buffer out of per-cpu storage so
+ * we can re-enable preemption.
+ */
+ tmppage = zswap_tmppage_alloc();
+ if (!tmppage) {
+ zswap_reject_tmppage_fail++;
+ ret = -ENOMEM;
+ goto freepage;
+ }
+ flush_attempted = 1;
+ tmpdst = page_address(tmppage);
+ memcpy(tmpdst, dst, dlen);
+ dst = tmpdst;
+ put_cpu_var(zswap_dstmem);
+
+ /* try to free up some space */
+ /* TODO: replace with more targeted policy */
+ zswap_flush_entries(type, 16);
+ /* try again, allowing wait */
+ handle = zs_malloc(tree->pool, dlen,
+ __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
+ __GFP_NOWARN);
+ if (!handle) {
+ /* still no space, fail */
+ zswap_reject_zsmalloc_fail++;
+ ret = -ENOMEM;
+ goto freepage;
+ }
+ zswap_saved_by_flush++;
+ }
+
+ buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
+ memcpy(buf, dst, dlen);
+ zs_unmap_object(tree->pool, handle);
+ if (flush_attempted)
+ zswap_tmppage_free(tmppage);
+ else
+ put_cpu_var(zswap_dstmem);
+
+ /* allocate entry */
+ entry = zswap_entry_cache_alloc(GFP_KERNEL);
+ if (!entry) {
+ zswap_reject_kmemcache_fail++;
+ ret = -ENOMEM;
+ goto reject;
+ }
+
+ /* populate entry */
+ entry->type = type;
+ entry->offset = offset;
+ entry->handle = handle;
+ entry->length = dlen;
+
+ /* map */
+ spin_lock(&tree->lock);
+ do {
+ ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
+ if (ret == -EEXIST) {
+ zswap_duplicate_entry++;
+ /* remove from rbtree and lru */
+ rb_erase(&dupentry->rbnode, &tree->rbroot);
+ if (dupentry->lru.next != LIST_POISON1)
+ list_del(&dupentry->lru);
+ if (!zswap_entry_put(dupentry)) {
+ /* free */
+ zs_free(tree->pool, dupentry->handle);
+ zswap_entry_cache_free(dupentry);
+ atomic_dec(&zswap_stored_pages);
+ }
+ }
+ } while (ret == -EEXIST);
+ list_add_tail(&entry->lru, &tree->lru);
+ spin_unlock(&tree->lock);
+
+ /* update stats */
+ atomic_inc(&zswap_stored_pages);
+
+ return 0;
+
+freepage:
+ if (flush_attempted)
+ zswap_tmppage_free(tmppage);
+ else
+ put_cpu_var(zswap_dstmem);
+reject:
+ return ret;
+}
+
+/*
+ * returns 0 if the page was successfully decompressed
+ * return -1 on entry not found or error
+*/
+static int zswap_frontswap_load(unsigned type, pgoff_t offset, struct page *page)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry;
+ u8 *src, *dst;
+ unsigned int dlen;
+ int refcount;
+
+ /* find */
+ spin_lock(&tree->lock);
+ entry = zswap_rb_search(&tree->rbroot, offset);
+ if (!entry) {
+ /* entry was flushed */
+ spin_unlock(&tree->lock);
+ return -1;
+ }
+ zswap_entry_get(entry);
+
+ /* remove from lru */
+ if (entry->lru.next != LIST_POISON1)
+ list_del(&entry->lru);
+ spin_unlock(&tree->lock);
+
+ /* decompress */
+ dlen = PAGE_SIZE;
+ src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
+ dst = kmap_atomic(page);
+ zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
+ dst, &dlen);
+ kunmap_atomic(dst);
+ zs_unmap_object(tree->pool, entry->handle);
+
+ spin_lock(&tree->lock);
+ refcount = zswap_entry_put(entry);
+ if (likely(refcount)) {
+ list_add_tail(&entry->lru, &tree->lru);
+ spin_unlock(&tree->lock);
+ return 0;
+ }
+ spin_unlock(&tree->lock);
+
+ /*
+ * We don't have to unlink from the rbtree because zswap_flush_entry()
+ * or zswap_frontswap_invalidate page() has already done this for us if we
+ * are the last reference.
+ */
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+
+ return 0;
+}
+
+/* invalidates a single page */
+static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct zswap_entry *entry;
+ int refcount;
+
+ if (!tree)
+ return;
+
+ /* find */
+ spin_lock(&tree->lock);
+ entry = zswap_rb_search(&tree->rbroot, offset);
+ if (!entry) {
+ /* entry was flushed */
+ spin_unlock(&tree->lock);
+ return;
+ }
+
+ /* remove from rbtree and lru */
+ rb_erase(&entry->rbnode, &tree->rbroot);
+ if (entry->lru.next != LIST_POISON1)
+ list_del(&entry->lru);
+ refcount = zswap_entry_put(entry);
+ spin_unlock(&tree->lock);
+ if (refcount) {
+ /* must be flushing */
+ return;
+ }
+
+ /* free */
+ zs_free(tree->pool, entry->handle);
+ zswap_entry_cache_free(entry);
+ atomic_dec(&zswap_stored_pages);
+}
+
+/* invalidates all pages for the given swap type */
+static void zswap_frontswap_invalidate_area(unsigned type)
+{
+ struct zswap_tree *tree = zswap_trees[type];
+ struct rb_node *node, *next;
+ struct zswap_entry *entry;
+
+ if (!tree)
+ return;
+
+ /* walk the tree and free everything */
+ spin_lock(&tree->lock);
+ node = rb_first(&tree->rbroot);
+ while (node) {
+ entry = rb_entry(node, struct zswap_entry, rbnode);
+ zs_free(tree->pool, entry->handle);
+ next = rb_next(node);
+ zswap_entry_cache_free(entry);
+ node = next;
+ }
+ tree->rbroot = RB_ROOT;
+ INIT_LIST_HEAD(&tree->lru);
+ spin_unlock(&tree->lock);
+}
+
+/* NOTE: this is called in atomic context from swapon and must not sleep */
+static void zswap_frontswap_init(unsigned type)
+{
+ struct zswap_tree *tree;
+
+ tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
+ if (!tree)
+ goto err;
+ tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
+ if (!tree->pool)
+ goto freetree;
+ tree->rbroot = RB_ROOT;
+ INIT_LIST_HEAD(&tree->lru);
+ spin_lock_init(&tree->lock);
+ zswap_trees[type] = tree;
+ return;
+
+freetree:
+ kfree(tree);
+err:
+ pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
+}
+
+static struct frontswap_ops zswap_frontswap_ops = {
+ .store = zswap_frontswap_store,
+ .load = zswap_frontswap_load,
+ .invalidate_page = zswap_frontswap_invalidate_page,
+ .invalidate_area = zswap_frontswap_invalidate_area,
+ .init = zswap_frontswap_init
+};
+
+/*********************************
+* debugfs functions
+**********************************/
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+
+static struct dentry *zswap_debugfs_root;
+
+static int __init zswap_debugfs_init(void)
+{
+ if (!debugfs_initialized())
+ return -ENODEV;
+
+ zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
+ if (!zswap_debugfs_root)
+ return -ENOMEM;
+
+ debugfs_create_u64("saved_by_flush", S_IRUGO,
+ zswap_debugfs_root, &zswap_saved_by_flush);
+ debugfs_create_u64("pool_limit_hit", S_IRUGO,
+ zswap_debugfs_root, &zswap_pool_limit_hit);
+ debugfs_create_u64("reject_flush_attempted", S_IRUGO,
+ zswap_debugfs_root, &zswap_flush_attempted);
+ debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_tmppage_fail);
+ debugfs_create_u64("reject_flush_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_flush_fail);
+ debugfs_create_u64("reject_zsmalloc_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_zsmalloc_fail);
+ debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_kmemcache_fail);
+ debugfs_create_u64("reject_compress_poor", S_IRUGO,
+ zswap_debugfs_root, &zswap_reject_compress_poor);
+ debugfs_create_u64("flushed_pages", S_IRUGO,
+ zswap_debugfs_root, &zswap_flushed_pages);
+ debugfs_create_u64("duplicate_entry", S_IRUGO,
+ zswap_debugfs_root, &zswap_duplicate_entry);
+ debugfs_create_atomic_t("pool_pages", S_IRUGO,
+ zswap_debugfs_root, &zswap_pool_pages);
+ debugfs_create_atomic_t("stored_pages", S_IRUGO,
+ zswap_debugfs_root, &zswap_stored_pages);
+ debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
+ zswap_debugfs_root, &zswap_outstanding_flushes);
+
+ return 0;
+}
+
+static void __exit zswap_debugfs_exit(void)
+{
+ if (zswap_debugfs_root)
+ debugfs_remove_recursive(zswap_debugfs_root);
+}
+#else
+static inline int __init zswap_debugfs_init(void)
+{
+ return 0;
+}
+
+static inline void __exit zswap_debugfs_exit(void) { }
+#endif
+
+/*********************************
+* module init and exit
+**********************************/
+static int __init init_zswap(void)
+{
+ if (!zswap_enabled)
+ return 0;
+
+ pr_info("loading zswap\n");
+ if (zswap_entry_cache_create()) {
+ pr_err("zswap: entry cache creation failed\n");
+ goto error;
+ }
+ if (zswap_page_pool_create()) {
+ pr_err("zswap: page pool initialization failed\n");
+ goto pagepoolfail;
+ }
+ if (zswap_tmppage_pool_create()) {
+ pr_err("zswap: workmem pool initialization failed\n");
+ goto tmppoolfail;
+ }
+ if (zswap_comp_init()) {
+ pr_err("zswap: compressor initialization failed\n");
+ goto compfail;
+ }
+ if (zswap_cpu_init()) {
+ pr_err("zswap: per-cpu initialization failed\n");
+ goto pcpufail;
+ }
+ frontswap_register_ops(&zswap_frontswap_ops);
+ if (zswap_debugfs_init())
+ pr_warn("zswap: debugfs initialization failed\n");
+ return 0;
+pcpufail:
+ zswap_comp_exit();
+compfail:
+ zswap_tmppage_pool_destroy();
+tmppoolfail:
+ zswap_page_pool_destroy();
+pagepoolfail:
+ zswap_entry_cache_destory();
+error:
+ return -ENOMEM;
+}
+/* must be late so crypto has time to come up */
+late_initcall(init_zswap);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
+MODULE_DESCRIPTION("Compression backend for frontswap pages");
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
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^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 6/6] zswap: add documentation
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 21:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
This patch adds the documentation file for the zswap functionality
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
Documentation/vm/zswap.txt | 73 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 73 insertions(+)
create mode 100644 Documentation/vm/zswap.txt
diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt
new file mode 100644
index 0000000..5d00ce9
--- /dev/null
+++ b/Documentation/vm/zswap.txt
@@ -0,0 +1,73 @@
+Overview:
+
+Zswap is a lightweight compressed cache for swap pages. It takes
+pages that are in the process of being swapped out and attempts to
+compress them into a dynamically allocated RAM-based memory pool.
+If this process is successful, the writeback to the swap device is
+deferred and, in many cases, avoided completely. This results in
+a significant I/O reduction and performance gains for systems that
+are swapping.
+
+Zswap provides compressed swap caching that basically trades CPU cycles
+for reduced swap I/O. This trade-off can result in a significant
+performance improvement as reads to/writes from to the compressed
+cache almost always faster that reading from a swap device
+which incurs the latency of an asynchronous block I/O read.
+
+Some potential benefits:
+* Desktop/laptop users with limited RAM capacities can mitigate the
+ performance impact of swapping.
+* Overcommitted guests that share a common I/O resource can
+ dramatically reduce their swap I/O pressure, avoiding heavy
+ handed I/O throttling by the hypervisor. This allows more work
+ to get done with less impact to the guest workload and guests
+ sharing the I/O subsystem
+* Users with SSDs as swap devices can extend the life of the device by
+ drastically reducing life-shortening writes.
+
+Zswap evicts pages from compressed cache on an LRU basis to the backing
+swap device when the compress pool reaches it size limit or the pool is
+unable to obtain additional pages from the buddy allocator. This
+requirement had been identified in prior community discussions.
+
+To enabled zswap, the "enabled" attribute must be set to 1 at boot time.
+e.g. zswap.enabled=1
+
+Design:
+
+Zswap receives pages for compression through the Frontswap API and
+is able to evict pages from its own compressed pool on an LRU basis
+and write them back to the backing swap device in the case that the
+compressed pool is full or unable to secure additional pages from
+the buddy allocator.
+
+Zswap makes use of zsmalloc for the managing the compressed memory
+pool. This is because zsmalloc is specifically designed to minimize
+fragmentation on large (> PAGE_SIZE/2) allocation sizes. Each
+allocation in zsmalloc is not directly accessible by address.
+Rather, a handle is return by the allocation routine and that handle
+must be mapped before being accessed. The compressed memory pool grows
+on demand and shrinks as compressed pages are freed. The pool is
+not preallocated.
+
+When a swap page is passed from frontswap to zswap, zswap maintains
+a mapping of the swap entry, a combination of the swap type and swap
+offset, to the zsmalloc handle that references that compressed swap
+page. This mapping is achieved with a red-black tree per swap type.
+The swap offset is the search key for the tree nodes.
+
+Zswap seeks to be simple in its policies. Sysfs attributes allow for
+two user controlled policies:
+* max_compression_ratio - Maximum compression ratio, as as percentage,
+ for an acceptable compressed page. Any page that does not compress
+ by at least this ratio will be rejected.
+* max_pool_percent - The maximum percentage of memory that the compressed
+ pool can occupy.
+
+Zswap allows the compressor to be selected at kernel boot time by
+setting the “compressor” attribute. The default compressor is lzo.
+e.g. zswap.compressor=deflate
+
+A debugfs interface is provided for various statistic about pool size,
+number of pages stored, and various counters for the reasons pages
+are rejected.
--
1.7.9.5
^ permalink raw reply related [flat|nested] 38+ messages in thread
* [PATCHv3 6/6] zswap: add documentation
@ 2013-01-28 21:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 21:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Seth Jennings, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
This patch adds the documentation file for the zswap functionality
Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
---
Documentation/vm/zswap.txt | 73 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 73 insertions(+)
create mode 100644 Documentation/vm/zswap.txt
diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt
new file mode 100644
index 0000000..5d00ce9
--- /dev/null
+++ b/Documentation/vm/zswap.txt
@@ -0,0 +1,73 @@
+Overview:
+
+Zswap is a lightweight compressed cache for swap pages. It takes
+pages that are in the process of being swapped out and attempts to
+compress them into a dynamically allocated RAM-based memory pool.
+If this process is successful, the writeback to the swap device is
+deferred and, in many cases, avoided completely.A This results in
+a significant I/O reduction and performance gains for systems that
+are swapping.
+
+Zswap provides compressed swap caching that basically trades CPU cycles
+for reduced swap I/O.A This trade-off can result in a significant
+performance improvement as reads to/writes from to the compressed
+cache almost always faster that reading from a swap device
+which incurs the latency of an asynchronous block I/O read.
+
+Some potential benefits:
+* Desktop/laptop users with limited RAM capacities can mitigate the
+A A A performance impact of swapping.
+* Overcommitted guests that share a common I/O resource can
+A A A dramatically reduce their swap I/O pressure, avoiding heavy
+A A A handed I/O throttling by the hypervisor.A This allows more work
+A A A to get done with less impact to the guest workload and guests
+A A A sharing the I/O subsystem
+* Users with SSDs as swap devices can extend the life of the device by
+A A A drastically reducing life-shortening writes.
+
+Zswap evicts pages from compressed cache on an LRU basis to the backing
+swap device when the compress pool reaches it size limit or the pool is
+unable to obtain additional pages from the buddy allocator.A This
+requirement had been identified in prior community discussions.
+
+To enabled zswap, the "enabled" attribute must be set to 1 at boot time.
+e.g. zswap.enabled=1
+
+Design:
+
+Zswap receives pages for compression through the Frontswap API and
+is able to evict pages from its own compressed pool on an LRU basis
+and write them back to the backing swap device in the case that the
+compressed pool is full or unable to secure additional pages from
+the buddy allocator.
+
+Zswap makes use of zsmalloc for the managing the compressed memory
+pool. This is because zsmalloc is specifically designed to minimize
+fragmentation on large (> PAGE_SIZE/2) allocation sizes. Each
+allocation in zsmalloc is not directly accessible by address.
+Rather, a handle is return by the allocation routine and that handle
+must be mapped before being accessed. The compressed memory pool grows
+on demand and shrinks as compressed pages are freed. The pool is
+not preallocated.
+
+When a swap page is passed from frontswap to zswap, zswap maintains
+a mapping of the swap entry, a combination of the swap type and swap
+offset, to the zsmalloc handle that references that compressed swap
+page. This mapping is achieved with a red-black tree per swap type.
+The swap offset is the search key for the tree nodes.
+
+Zswap seeks to be simple in its policies. Sysfs attributes allow for
+two user controlled policies:
+* max_compression_ratio - Maximum compression ratio, as as percentage,
+ for an acceptable compressed page. Any page that does not compress
+ by at least this ratio will be rejected.
+* max_pool_percent - The maximum percentage of memory that the compressed
+ pool can occupy.
+
+Zswap allows the compressor to be selected at kernel boot time by
+setting the a??compressora?? attribute. The default compressor is lzo.
+e.g. zswap.compressor=deflate
+
+A debugfs interface is provided for various statistic about pool size,
+number of pages stored, and various counters for the reasons pages
+are rejected.
--
1.7.9.5
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply related [flat|nested] 38+ messages in thread
* Re: [PATCHv3 0/6] zswap: compressed swap caching
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 22:08 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 22:08 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On 01/28/2013 03:49 PM, Seth Jennings wrote:
> Changelog:
>
> v3:
> * Dropped the zsmalloc patches from the set, except the promotion patch
> which has be converted to a rename patch (vs full diff). The dropped
> patches have been Acked and are going into Greg's staging tree soon.
> * Separated [PATCHv2 7/9] into two patches since it makes changes for two
> different reasons (Minchan)
> * Moved ZSWAP_MAX_OUTSTANDING_FLUSHES near the top in zswap.c (Rik)
> * Rebase to v3.8-rc5. linux-next is a little volatile with the
> swapper_space per type changes which will effect this patchset.
This patchset will apply but not build on v3.8-rc5 without the
zsmalloc patchset here:
https://lkml.org/lkml/2013/1/25/486
The zsmalloc patches don't apply cleanly without this patch:
https://lkml.org/lkml/2013/1/4/298
Nothing has changed functionally from v2, so it would probably be
easier to do any testing from that version. However, if you want to
apply this latest version, those are the prerequisite patches.
Or your can pull from here:
git://github.com/spartacus06/linux.git zswap-v3
Seth
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 0/6] zswap: compressed swap caching
@ 2013-01-28 22:08 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-28 22:08 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On 01/28/2013 03:49 PM, Seth Jennings wrote:
> Changelog:
>
> v3:
> * Dropped the zsmalloc patches from the set, except the promotion patch
> which has be converted to a rename patch (vs full diff). The dropped
> patches have been Acked and are going into Greg's staging tree soon.
> * Separated [PATCHv2 7/9] into two patches since it makes changes for two
> different reasons (Minchan)
> * Moved ZSWAP_MAX_OUTSTANDING_FLUSHES near the top in zswap.c (Rik)
> * Rebase to v3.8-rc5. linux-next is a little volatile with the
> swapper_space per type changes which will effect this patchset.
This patchset will apply but not build on v3.8-rc5 without the
zsmalloc patchset here:
https://lkml.org/lkml/2013/1/25/486
The zsmalloc patches don't apply cleanly without this patch:
https://lkml.org/lkml/2013/1/4/298
Nothing has changed functionally from v2, so it would probably be
easier to do any testing from that version. However, if you want to
apply this latest version, those are the prerequisite patches.
Or your can pull from here:
git://github.com/spartacus06/linux.git zswap-v3
Seth
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 2/6] zsmalloc: promote to lib/
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 23:56 ` Minchan Kim
-1 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-28 23:56 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Mon, Jan 28, 2013 at 03:49:23PM -0600, Seth Jennings wrote:
> This patch promotes the slab-based zsmalloc memory allocator
> from the staging tree to lib/
>
> zswap depends on this allocator for storing compressed RAM pages
> in an efficient way under system wide memory pressure where
> high-order (greater than 0) page allocation are very likely to
> fail.
>
> For more information on zsmalloc and its internals, read the
> documentation at the top of the zsmalloc.c file.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
At least, maintainer should notice about known bug of zsmalloc.
http://marc.info/?l=linux-mm&m=135933481517809&w=3
--
Kind regards,
Minchan Kim
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 2/6] zsmalloc: promote to lib/
@ 2013-01-28 23:56 ` Minchan Kim
0 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-28 23:56 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Mon, Jan 28, 2013 at 03:49:23PM -0600, Seth Jennings wrote:
> This patch promotes the slab-based zsmalloc memory allocator
> from the staging tree to lib/
>
> zswap depends on this allocator for storing compressed RAM pages
> in an efficient way under system wide memory pressure where
> high-order (greater than 0) page allocation are very likely to
> fail.
>
> For more information on zsmalloc and its internals, read the
> documentation at the top of the zsmalloc.c file.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
At least, maintainer should notice about known bug of zsmalloc.
http://marc.info/?l=linux-mm&m=135933481517809&w=3
--
Kind regards,
Minchan Kim
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 3/6] mm: break up swap_writepage() for frontswap backends
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-28 23:58 ` Minchan Kim
-1 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-28 23:58 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Mon, Jan 28, 2013 at 03:49:24PM -0600, Seth Jennings wrote:
> swap_writepage() is currently where frontswap hooks into the swap
> write path to capture pages with the frontswap_store() function.
> However, if a frontswap backend wants to "resume" the writeback of
> a page to the swap device, it can't call swap_writepage() as
> the page will simply reenter the backend.
>
> This patch separates swap_writepage() into a top and bottom half, the
> bottom half named __swap_writepage() to allow a frontswap backend,
> like zswap, to resume writeback beyond the frontswap_store() hook.
>
> __add_to_swap_cache() is also made non-static so that the page for
> which writeback is to be resumed can be added to the swap cache.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
--
Kind regards,
Minchan Kim
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 3/6] mm: break up swap_writepage() for frontswap backends
@ 2013-01-28 23:58 ` Minchan Kim
0 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-28 23:58 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Mon, Jan 28, 2013 at 03:49:24PM -0600, Seth Jennings wrote:
> swap_writepage() is currently where frontswap hooks into the swap
> write path to capture pages with the frontswap_store() function.
> However, if a frontswap backend wants to "resume" the writeback of
> a page to the swap device, it can't call swap_writepage() as
> the page will simply reenter the backend.
>
> This patch separates swap_writepage() into a top and bottom half, the
> bottom half named __swap_writepage() to allow a frontswap backend,
> like zswap, to resume writeback beyond the frontswap_store() hook.
>
> __add_to_swap_cache() is also made non-static so that the page for
> which writeback is to be resumed can be added to the swap cache.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
--
Kind regards,
Minchan Kim
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 4/6] mm: allow for outstanding swap writeback accounting
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-29 0:01 ` Minchan Kim
-1 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-29 0:01 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Mon, Jan 28, 2013 at 03:49:25PM -0600, Seth Jennings wrote:
> To prevent flooding the swap device with writebacks, frontswap
> backends need to count and limit the number of outstanding
> writebacks. The incrementing of the counter can be done before
> the call to __swap_writepage(). However, the caller must receive
> a notification when the writeback completes in order to decrement
> the counter.
>
> To achieve this functionality, this patch modifies
> __swap_writepage() to take the bio completion callback function
> as an argument.
>
> end_swap_bio_write(), the normal bio completion function, is also
> made non-static so that code doing the accounting can call it
> after the accounting is done.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
--
Kind regards,
Minchan Kim
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 4/6] mm: allow for outstanding swap writeback accounting
@ 2013-01-29 0:01 ` Minchan Kim
0 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-29 0:01 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Mon, Jan 28, 2013 at 03:49:25PM -0600, Seth Jennings wrote:
> To prevent flooding the swap device with writebacks, frontswap
> backends need to count and limit the number of outstanding
> writebacks. The incrementing of the counter can be done before
> the call to __swap_writepage(). However, the caller must receive
> a notification when the writeback completes in order to decrement
> the counter.
>
> To achieve this functionality, this patch modifies
> __swap_writepage() to take the bio completion callback function
> as an argument.
>
> end_swap_bio_write(), the normal bio completion function, is also
> made non-static so that code doing the accounting can call it
> after the accounting is done.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
--
Kind regards,
Minchan Kim
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-29 6:27 ` Minchan Kim
-1 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-29 6:27 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
First feeling is it's simple and nice approach.
Although we have some problems to decide policy, it could solve by later patch
so I hope we make basic infrasture more solid by lots of comment.
There are two things to review hard.
1. data structure life - when any data structure is died by whom?
Please write down it in changelog or header of zswap.c
2. Flush routine - I hope it would be nice to separate it as another
incremental patches if it is possible. If it's impossible, let's add
lots of words.
On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
> zswap is a thin compression backend for frontswap. It receives
> pages from frontswap and attempts to store them in a compressed
> memory pool, resulting in an effective partial memory reclaim and
> dramatically reduced swap device I/O.
>
> Additional, in most cases, pages can be retrieved from this
> compressed store much more quickly than reading from tradition
> swap devices resulting in faster performance for many workloads.
>
> This patch adds the zswap driver to mm/
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> ---
> mm/Kconfig | 15 +
> mm/Makefile | 1 +
> mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 1089 insertions(+)
> create mode 100644 mm/zswap.c
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 278e3ab..14b9acb 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -446,3 +446,18 @@ config FRONTSWAP
> and swap data is stored as normal on the matching swap device.
>
> If unsure, say Y to enable frontswap.
> +
> +config ZSWAP
> + bool "In-kernel swap page compression"
> + depends on FRONTSWAP && CRYPTO
Couldn't we support CRYPTO optionally?
> + select CRYPTO_LZO
> + select ZSMALLOC
> + default n
> + help
> + Zswap is a backend for the frontswap mechanism in the VMM.
> + It receives pages from frontswap and attempts to store them
> + in a compressed memory pool, resulting in an effective
> + partial memory reclaim. In addition, pages and be retrieved
> + from this compressed store much faster than most tradition
> + swap devices resulting in reduced I/O and faster performance
> + for many workloads.
> diff --git a/mm/Makefile b/mm/Makefile
> index 3a46287..1b1ed5c 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
> obj-$(CONFIG_BOUNCE) += bounce.o
> obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
> obj-$(CONFIG_FRONTSWAP) += frontswap.o
> +obj-$(CONFIG_ZSWAP) += zswap.o
> obj-$(CONFIG_HAS_DMA) += dmapool.o
> obj-$(CONFIG_HUGETLBFS) += hugetlb.o
> obj-$(CONFIG_NUMA) += mempolicy.o
> diff --git a/mm/zswap.c b/mm/zswap.c
> new file mode 100644
> index 0000000..050b6db
> --- /dev/null
> +++ b/mm/zswap.c
> @@ -0,0 +1,1073 @@
> +/*
> + * zswap-drv.c - zswap driver file
> + *
> + * zswap is a backend for frontswap that takes pages that are in the
> + * process of being swapped out and attempts to compress them and store
> + * them in a RAM-based memory pool. This results in a significant I/O
> + * reduction on the real swap device and, in the case of a slow swap
> + * device, can also improve workload performance.
> + *
> + * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> +*/
> +
> +#include <linux/module.h>
> +#include <linux/cpu.h>
> +#include <linux/highmem.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +#include <linux/atomic.h>
> +#include <linux/frontswap.h>
> +#include <linux/rbtree.h>
> +#include <linux/swap.h>
> +#include <linux/crypto.h>
> +#include <linux/mempool.h>
> +#include <linux/zsmalloc.h>
> +
> +#include <linux/mm_types.h>
> +#include <linux/page-flags.h>
> +#include <linux/swapops.h>
> +#include <linux/writeback.h>
> +#include <linux/pagemap.h>
> +
> +/*********************************
> +* statistics
> +**********************************/
> +/* Number of memory pages used by the compressed pool */
> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
> +/* The number of compressed pages currently stored in zswap */
> +static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
> +/* The number of outstanding pages awaiting writeback */
> +static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
> +
> +/*
> + * The statistics below are not protected from concurrent access for
> + * performance reasons so they may not be a 100% accurate. However,
> + * the do provide useful information on roughly how many times a
> + * certain event is occurring.
> +*/
> +static u64 zswap_flushed_pages;
> +static u64 zswap_reject_compress_poor;
> +static u64 zswap_flush_attempted;
> +static u64 zswap_reject_tmppage_fail;
> +static u64 zswap_reject_flush_fail;
> +static u64 zswap_reject_zsmalloc_fail;
> +static u64 zswap_reject_kmemcache_fail;
> +static u64 zswap_saved_by_flush;
> +static u64 zswap_duplicate_entry;
> +
> +/*********************************
> +* tunables
> +**********************************/
> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
> +static bool zswap_enabled;
> +module_param_named(enabled, zswap_enabled, bool, 0);
It seems default is disable at the moment?
> +
> +/* Compressor to be used by zswap (fixed at boot for now) */
> +#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> +module_param_named(compressor, zswap_compressor, charp, 0);
> +
> +/* The maximum percentage of memory that the compressed pool can occupy */
> +static unsigned int zswap_max_pool_percent = 20;
> +module_param_named(max_pool_percent,
> + zswap_max_pool_percent, uint, 0644);
> +
> +/*
> + * Maximum compression ratio, as as percentage, for an acceptable
> + * compressed page. Any pages that do not compress by at least
> + * this ratio will be rejected.
> +*/
> +static unsigned int zswap_max_compression_ratio = 80;
> +module_param_named(max_compression_ratio,
> + zswap_max_compression_ratio, uint, 0644);
> +
> +/*
> + * Maximum number of outstanding flushes allowed at any given time.
> + * This is to prevent decompressing an unbounded number of compressed
> + * pages into the swap cache all at once, and to help with writeback
> + * congestion.
> +*/
> +#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
> +
> +/*********************************
> +* compression functions
> +**********************************/
> +/* per-cpu compression transforms */
> +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
> +
> +enum comp_op {
> + ZSWAP_COMPOP_COMPRESS,
> + ZSWAP_COMPOP_DECOMPRESS
> +};
> +
> +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
> + u8 *dst, unsigned int *dlen)
> +{
> + struct crypto_comp *tfm;
> + int ret;
> +
> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
> + switch (op) {
> + case ZSWAP_COMPOP_COMPRESS:
> + ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
> + break;
> + case ZSWAP_COMPOP_DECOMPRESS:
> + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
> + break;
> + default:
> + ret = -EINVAL;
> + }
> +
> + put_cpu();
> + return ret;
> +}
> +
> +static int __init zswap_comp_init(void)
> +{
> + if (!crypto_has_comp(zswap_compressor, 0, 0)) {
> + pr_info("zswap: %s compressor not available\n",
> + zswap_compressor);
> + /* fall back to default compressor */
> + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> + if (!crypto_has_comp(zswap_compressor, 0, 0))
> + /* can't even load the default compressor */
> + return -ENODEV;
> + }
> + pr_info("zswap: using %s compressor\n", zswap_compressor);
> +
> + /* alloc percpu transforms */
> + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
> + if (!zswap_comp_pcpu_tfms)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +static void zswap_comp_exit(void)
> +{
> + /* free percpu transforms */
> + if (zswap_comp_pcpu_tfms)
> + free_percpu(zswap_comp_pcpu_tfms);
> +}
> +
> +/*********************************
> +* data structures
> +**********************************/
> +struct zswap_entry {
> + struct rb_node rbnode;
> + struct list_head lru;
> + int refcount;
> + unsigned type;
> + pgoff_t offset;
> + unsigned long handle;
> + unsigned int length;
> +};
> +
> +/*
> + * The tree lock in the zswap_tree struct protects a few things:
> + * - the rbtree
> + * - the lru list
> + * - the refcount field of each entry in the tree
> + */
> +struct zswap_tree {
> + struct rb_root rbroot;
> + struct list_head lru;
> + spinlock_t lock;
> + struct zs_pool *pool;
> +};
> +
> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
> +
> +/*********************************
> +* zswap entry functions
> +**********************************/
> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
> +static struct kmem_cache *zswap_entry_cache;
> +
> +static inline int zswap_entry_cache_create(void)
> +{
> + zswap_entry_cache =
> + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
> + sizeof(struct zswap_entry), 0, 0, NULL);
> + return (zswap_entry_cache == NULL);
> +}
> +
> +static inline void zswap_entry_cache_destory(void)
> +{
> + kmem_cache_destroy(zswap_entry_cache);
> +}
> +
> +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
> +{
> + struct zswap_entry *entry;
> + entry = kmem_cache_alloc(zswap_entry_cache, gfp);
> + if (!entry)
> + return NULL;
> + INIT_LIST_HEAD(&entry->lru);
> + entry->refcount = 1;
> + return entry;
> +}
> +
> +static inline void zswap_entry_cache_free(struct zswap_entry *entry)
> +{
> + kmem_cache_free(zswap_entry_cache, entry);
> +}
> +
> +static inline void zswap_entry_get(struct zswap_entry *entry)
> +{
> + entry->refcount++;
> +}
> +
> +static inline int zswap_entry_put(struct zswap_entry *entry)
> +{
> + entry->refcount--;
> + return entry->refcount;
> +}
> +
> +/*********************************
> +* rbtree functions
> +**********************************/
> +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
> +{
> + struct rb_node *node = root->rb_node;
> + struct zswap_entry *entry;
> +
> + while (node) {
> + entry = rb_entry(node, struct zswap_entry, rbnode);
> + if (entry->offset > offset)
> + node = node->rb_left;
> + else if (entry->offset < offset)
> + node = node->rb_right;
> + else
> + return entry;
> + }
> + return NULL;
> +}
> +
> +/*
> + * In the case that a entry with the same offset is found, it a pointer to
> + * the existing entry is stored in dupentry and the function returns -EEXIST
> +*/
> +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
> + struct zswap_entry **dupentry)
> +{
> + struct rb_node **link = &root->rb_node, *parent = NULL;
> + struct zswap_entry *myentry;
> +
> + while (*link) {
> + parent = *link;
> + myentry = rb_entry(parent, struct zswap_entry, rbnode);
> + if (myentry->offset > entry->offset)
> + link = &(*link)->rb_left;
> + else if (myentry->offset < entry->offset)
> + link = &(*link)->rb_right;
> + else {
> + *dupentry = myentry;
> + return -EEXIST;
> + }
> + }
> + rb_link_node(&entry->rbnode, parent, link);
> + rb_insert_color(&entry->rbnode, root);
> + return 0;
> +}
> +
> +/*********************************
> +* per-cpu code
> +**********************************/
> +static DEFINE_PER_CPU(u8 *, zswap_dstmem);
> +
> +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
> +{
> + struct crypto_comp *tfm;
> + u8 *dst;
> +
> + switch (action) {
> + case CPU_UP_PREPARE:
> + tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
> + if (IS_ERR(tfm)) {
> + pr_err("zswap: can't allocate compressor transform\n");
> + return NOTIFY_BAD;
> + }
> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
> + dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
> + if (!dst) {
> + pr_err("zswap: can't allocate compressor buffer\n");
> + crypto_free_comp(tfm);
> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> + return NOTIFY_BAD;
> + }
> + per_cpu(zswap_dstmem, cpu) = dst;
> + break;
> + case CPU_DEAD:
> + case CPU_UP_CANCELED:
> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
> + if (tfm) {
> + crypto_free_comp(tfm);
> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> + }
> + dst = per_cpu(zswap_dstmem, cpu);
> + if (dst) {
> + free_pages((unsigned long)dst, 1);
> + per_cpu(zswap_dstmem, cpu) = NULL;
> + }
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> +static int zswap_cpu_notifier(struct notifier_block *nb,
> + unsigned long action, void *pcpu)
> +{
> + unsigned long cpu = (unsigned long)pcpu;
> + return __zswap_cpu_notifier(action, cpu);
> +}
> +
> +static struct notifier_block zswap_cpu_notifier_block = {
> + .notifier_call = zswap_cpu_notifier
> +};
> +
> +static int zswap_cpu_init(void)
> +{
> + unsigned long cpu;
> +
> + get_online_cpus();
> + for_each_online_cpu(cpu)
> + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
> + goto cleanup;
> + register_cpu_notifier(&zswap_cpu_notifier_block);
> + put_online_cpus();
> + return 0;
> +
> +cleanup:
> + for_each_online_cpu(cpu)
> + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
> + put_online_cpus();
> + return -ENOMEM;
> +}
> +
> +/*********************************
> +* zsmalloc callbacks
> +**********************************/
> +static mempool_t *zswap_page_pool;
> +
> +static u64 zswap_pool_limit_hit;
> +
> +static inline unsigned int zswap_max_pool_pages(void)
> +{
> + return zswap_max_pool_percent * totalram_pages / 100;
> +}
> +
> +static inline int zswap_page_pool_create(void)
> +{
> + zswap_page_pool = mempool_create_page_pool(256, 0);
Could you write down why you select pool to 256?
If you have a plan, please write down it as TODO.
I think it could be a function of zswap_max_pool_pages with min/max.
Another question.
What's the benefit of using mempool for zsmalloc?
As you know, zsmalloc doesn't use mempool as default.
I guess you see some benefit. if so, zram could be changed.
If we can change zsmalloc's default scheme to use mempool,
all of customer of zsmalloc could be enhanced, too.
> + if (!zswap_page_pool)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +static inline void zswap_page_pool_destroy(void)
> +{
> + mempool_destroy(zswap_page_pool);
> +}
> +
> +static struct page *zswap_alloc_page(gfp_t flags)
> +{
> + struct page *page;
> +
> + if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
> + zswap_pool_limit_hit++;
> + return NULL;
> + }
> + page = mempool_alloc(zswap_page_pool, flags);
> + if (page)
> + atomic_inc(&zswap_pool_pages);
> + return page;
> +}
> +
> +static void zswap_free_page(struct page *page)
> +{
> + mempool_free(page, zswap_page_pool);
> + atomic_dec(&zswap_pool_pages);
Nit.
By semantic, free function can receive NULL argument so
atomic_dec would be nice to check it before decreasing count.
> +}
> +
> +static struct zs_ops zswap_zs_ops = {
> + .alloc = zswap_alloc_page,
> + .free = zswap_free_page
> +};
> +
> +/*********************************
> +* flush code
> +**********************************/
> +static void zswap_end_swap_write(struct bio *bio, int err)
> +{
> + end_swap_bio_write(bio, err);
> + atomic_dec(&zswap_outstanding_flushes);
> + zswap_flushed_pages++;
> +}
> +
> +/*
> + * zswap_get_swap_cache_page
> + *
> + * This is an adaption of read_swap_cache_async()
> + *
> + * If success, page is returned in retpage
> + * Returns 0 if page was already in the swap cache, page is not locked
> + * Returns 1 if the new page needs to be populated, page is locked
> + */
> +static int zswap_get_swap_cache_page(swp_entry_t entry,
> + struct page **retpage)
> +{
> + struct page *found_page, *new_page = NULL;
> + int err;
> +
> + *retpage = NULL;
> + do {
> + /*
> + * First check the swap cache. Since this is normally
> + * called after lookup_swap_cache() failed, re-calling
> + * that would confuse statistics.
> + */
> + found_page = find_get_page(&swapper_space, entry.val);
> + if (found_page)
> + break;
> +
> + /*
> + * Get a new page to read into from swap.
> + */
> + if (!new_page) {
> + new_page = alloc_page(GFP_KERNEL);
> + if (!new_page)
> + break; /* Out of memory */
> + }
> +
> + /*
> + * call radix_tree_preload() while we can wait.
> + */
> + err = radix_tree_preload(GFP_KERNEL);
> + if (err)
> + break;
> +
> + /*
> + * Swap entry may have been freed since our caller observed it.
> + */
> + err = swapcache_prepare(entry);
> + if (err == -EEXIST) { /* seems racy */
> + radix_tree_preload_end();
> + continue;
> + }
> + if (err) { /* swp entry is obsolete ? */
> + radix_tree_preload_end();
> + break;
> + }
> +
> + /* May fail (-ENOMEM) if radix-tree node allocation failed. */
> + __set_page_locked(new_page);
> + SetPageSwapBacked(new_page);
> + err = __add_to_swap_cache(new_page, entry);
> + if (likely(!err)) {
> + radix_tree_preload_end();
> + lru_cache_add_anon(new_page);
> + *retpage = new_page;
> + return 1;
> + }
> + radix_tree_preload_end();
> + ClearPageSwapBacked(new_page);
> + __clear_page_locked(new_page);
> + /*
> + * add_to_swap_cache() doesn't return -EEXIST, so we can safely
> + * clear SWAP_HAS_CACHE flag.
> + */
> + swapcache_free(entry, NULL);
> + } while (err != -ENOMEM);
> +
> + if (new_page)
> + page_cache_release(new_page);
> + if (!found_page)
> + return -ENOMEM;
> + *retpage = found_page;
> + return 0;
> +}
> +
> +static int zswap_flush_entry(struct zswap_entry *entry)
> +{
> + unsigned long type = entry->type;
> + struct zswap_tree *tree = zswap_trees[type];
> + struct page *page;
> + swp_entry_t swpentry;
> + u8 *src, *dst;
> + unsigned int dlen;
> + int ret, refcount;
> + struct writeback_control wbc = {
> + .sync_mode = WB_SYNC_NONE,
> + };
> +
> + /* get/allocate page in the swap cache */
> + swpentry = swp_entry(type, entry->offset);
> + ret = zswap_get_swap_cache_page(swpentry, &page);
> + if (ret < 0)
> + return ret;
> + else if (ret) {
> + /* decompress */
> + dlen = PAGE_SIZE;
> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
> + dst = kmap_atomic(page);
> + ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
> + dst, &dlen);
> + kunmap_atomic(dst);
> + zs_unmap_object(tree->pool, entry->handle);
> + BUG_ON(ret);
> + BUG_ON(dlen != PAGE_SIZE);
> + SetPageUptodate(page);
> + } else {
> + /* page is already in the swap cache, ignore for now */
> + spin_lock(&tree->lock);
> + refcount = zswap_entry_put(entry);
> + spin_unlock(&tree->lock);
> +
> + if (likely(refcount))
> + return 0;
> +
> + /* if the refcount is zero, invalidate must have come in */
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +
> + return 0;
> + }
> +
> + /* start writeback */
> + SetPageReclaim(page);
> + /*
> + * Return value is ignored here because it doesn't change anything
> + * for us. Page is returned unlocked.
> + */
> + (void)__swap_writepage(page, &wbc, zswap_end_swap_write);
> + page_cache_release(page);
> + atomic_inc(&zswap_outstanding_flushes);
> +
> + /* remove */
> + spin_lock(&tree->lock);
> + refcount = zswap_entry_put(entry);
> + if (refcount > 1) {
> + /* load in progress, load will free */
> + spin_unlock(&tree->lock);
> + return 0;
> + }
> + if (refcount == 1)
> + /* no invalidate yet, remove from rbtree */
> + rb_erase(&entry->rbnode, &tree->rbroot);
> + spin_unlock(&tree->lock);
> +
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +
> + return 0;
> +}
> +
> +static void zswap_flush_entries(unsigned type, int nr)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry;
> + int i, ret;
> +
> +/*
> + * This limits is arbitrary for now until a better
> + * policy can be implemented. This is so we don't
> + * eat all of RAM decompressing pages for writeback.
> + */
> + if (atomic_read(&zswap_outstanding_flushes) >
> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
> + return;
> +
> + for (i = 0; i < nr; i++) {
> + /* dequeue from lru */
> + spin_lock(&tree->lock);
> + if (list_empty(&tree->lru)) {
> + spin_unlock(&tree->lock);
> + break;
> + }
> + entry = list_first_entry(&tree->lru,
> + struct zswap_entry, lru);
> + list_del(&entry->lru);
> + zswap_entry_get(entry);
> + spin_unlock(&tree->lock);
> + ret = zswap_flush_entry(entry);
> + if (ret) {
> + /* put back on the lru */
> + spin_lock(&tree->lock);
> + list_add(&entry->lru, &tree->lru);
> + spin_unlock(&tree->lock);
> + } else {
> + if (atomic_read(&zswap_outstanding_flushes) >
> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
> + break;
> + }
> + }
> +}
The flush part complexity is very high so we needs careful review.
I hope you can make the patch step by step from ugly approach to smart one.
It helps reviewers much.
If it isn't easy, I will review as it is.
> +
> +/*******************************************
> +* page pool for temporary compression result
> +********************************************/
> +#define ZSWAP_TMPPAGE_POOL_PAGES 16
> +static LIST_HEAD(zswap_tmppage_list);
> +static DEFINE_SPINLOCK(zswap_tmppage_lock);
> +
> +static void zswap_tmppage_pool_destroy(void)
> +{
> + struct page *page, *tmppage;
> +
> + spin_lock(&zswap_tmppage_lock);
> + list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
> + list_del(&page->lru);
> + __free_pages(page, 1);
> + }
> + spin_unlock(&zswap_tmppage_lock);
> +}
> +
> +static int zswap_tmppage_pool_create(void)
> +{
> + int i;
> + struct page *page;
> +
> + for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
> + page = alloc_pages(GFP_KERNEL, 1);
> + if (!page) {
> + zswap_tmppage_pool_destroy();
> + return -ENOMEM;
> + }
> + spin_lock(&zswap_tmppage_lock);
> + list_add(&page->lru, &zswap_tmppage_list);
> + spin_unlock(&zswap_tmppage_lock);
> + }
> + return 0;
> +}
> +
> +static inline struct page *zswap_tmppage_alloc(void)
> +{
> + struct page *page;
> +
> + spin_lock(&zswap_tmppage_lock);
> + if (list_empty(&zswap_tmppage_list)) {
> + spin_unlock(&zswap_tmppage_lock);
> + return NULL;
> + }
> + page = list_first_entry(&zswap_tmppage_list, struct page, lru);
> + list_del(&page->lru);
> + spin_unlock(&zswap_tmppage_lock);
> + return page;
> +}
> +
> +static inline void zswap_tmppage_free(struct page *page)
> +{
> + spin_lock(&zswap_tmppage_lock);
> + list_add(&page->lru, &zswap_tmppage_list);
> + spin_unlock(&zswap_tmppage_lock);
> +}
> +
> +/*********************************
> +* frontswap hooks
> +**********************************/
> +/* attempts to compress and store an single page */
> +static int zswap_frontswap_store(unsigned type, pgoff_t offset, struct page *page)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry, *dupentry;
> + int ret;
> + unsigned int dlen = PAGE_SIZE;
> + unsigned long handle;
> + char *buf;
> + u8 *src, *dst, *tmpdst;
> + struct page *tmppage;
> + bool flush_attempted = 0;
> +
> + if (!tree) {
> + ret = -ENODEV;
> + goto reject;
> + }
> +
> + /* compress */
> + dst = get_cpu_var(zswap_dstmem);
> + src = kmap_atomic(page);
> + ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
> + kunmap_atomic(src);
> + if (ret) {
> + ret = -EINVAL;
> + goto freepage;
> + }
> + if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
> + zswap_reject_compress_poor++;
> + ret = -E2BIG;
> + goto freepage;
> + }
> +
> + /* store */
> + handle = zs_malloc(tree->pool, dlen,
> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
> + __GFP_NOWARN);
> + if (!handle) {
> + zswap_flush_attempted++;
> + /*
> + * Copy compressed buffer out of per-cpu storage so
> + * we can re-enable preemption.
> + */
> + tmppage = zswap_tmppage_alloc();
> + if (!tmppage) {
> + zswap_reject_tmppage_fail++;
> + ret = -ENOMEM;
> + goto freepage;
> + }
> + flush_attempted = 1;
> + tmpdst = page_address(tmppage);
> + memcpy(tmpdst, dst, dlen);
> + dst = tmpdst;
> + put_cpu_var(zswap_dstmem);
> +
> + /* try to free up some space */
> + /* TODO: replace with more targeted policy */
> + zswap_flush_entries(type, 16);
> + /* try again, allowing wait */
> + handle = zs_malloc(tree->pool, dlen,
> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
> + __GFP_NOWARN);
> + if (!handle) {
> + /* still no space, fail */
> + zswap_reject_zsmalloc_fail++;
> + ret = -ENOMEM;
> + goto freepage;
> + }
> + zswap_saved_by_flush++;
> + }
> +
> + buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
> + memcpy(buf, dst, dlen);
> + zs_unmap_object(tree->pool, handle);
> + if (flush_attempted)
> + zswap_tmppage_free(tmppage);
> + else
> + put_cpu_var(zswap_dstmem);
> +
> + /* allocate entry */
> + entry = zswap_entry_cache_alloc(GFP_KERNEL);
> + if (!entry) {
zs_free
> + zswap_reject_kmemcache_fail++;
> + ret = -ENOMEM;
> + goto reject;
> + }
> +
> + /* populate entry */
> + entry->type = type;
> + entry->offset = offset;
> + entry->handle = handle;
> + entry->length = dlen;
> +
> + /* map */
> + spin_lock(&tree->lock);
> + do {
> + ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
Could you describe why existing entry could be there?
IIUC, it is caused by delayed swap slot free of VM. Right?
Anyway, it would be nice to add comment about it.
> + if (ret == -EEXIST) {
> + zswap_duplicate_entry++;
> + /* remove from rbtree and lru */
> + rb_erase(&dupentry->rbnode, &tree->rbroot);
> + if (dupentry->lru.next != LIST_POISON1)
Why do we need this check? Is there any case entry isn't linked at LRU list?
Because you already removed it in load part. Right?
Let's add comment about that. And let's not dependent on LIST_POISON1 of
list util but use explicit zswap's one.
> + list_del(&dupentry->lru);
> + if (!zswap_entry_put(dupentry)) {
> + /* free */
> + zs_free(tree->pool, dupentry->handle);
> + zswap_entry_cache_free(dupentry);
> + atomic_dec(&zswap_stored_pages);
> + }
> + }
> + } while (ret == -EEXIST);
> + list_add_tail(&entry->lru, &tree->lru);
> + spin_unlock(&tree->lock);
> +
> + /* update stats */
> + atomic_inc(&zswap_stored_pages);
> +
> + return 0;
> +
> +freepage:
> + if (flush_attempted)
> + zswap_tmppage_free(tmppage);
> + else
> + put_cpu_var(zswap_dstmem);
> +reject:
> + return ret;
> +}
> +
> +/*
> + * returns 0 if the page was successfully decompressed
> + * return -1 on entry not found or error
> +*/
> +static int zswap_frontswap_load(unsigned type, pgoff_t offset, struct page *page)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry;
> + u8 *src, *dst;
> + unsigned int dlen;
> + int refcount;
> +
> + /* find */
> + spin_lock(&tree->lock);
> + entry = zswap_rb_search(&tree->rbroot, offset);
> + if (!entry) {
> + /* entry was flushed */
> + spin_unlock(&tree->lock);
> + return -1;
> + }
> + zswap_entry_get(entry);
> +
> + /* remove from lru */
> + if (entry->lru.next != LIST_POISON1)
When do we encounter this case?
By racing with flush?
Need comment, too.
> + list_del(&entry->lru);
> + spin_unlock(&tree->lock);
> +
> + /* decompress */
> + dlen = PAGE_SIZE;
> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
> + dst = kmap_atomic(page);
> + zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
> + dst, &dlen);
> + kunmap_atomic(dst);
> + zs_unmap_object(tree->pool, entry->handle);
> +
> + spin_lock(&tree->lock);
> + refcount = zswap_entry_put(entry);
> + if (likely(refcount)) {
> + list_add_tail(&entry->lru, &tree->lru);
> + spin_unlock(&tree->lock);
> + return 0;
> + }
> + spin_unlock(&tree->lock);
> +
> + /*
> + * We don't have to unlink from the rbtree because zswap_flush_entry()
> + * or zswap_frontswap_invalidate page() has already done this for us if we
> + * are the last reference.
> + */
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +
> + return 0;
> +}
> +
> +/* invalidates a single page */
> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry;
> + int refcount;
> +
> + if (!tree)
When do we encounter this case?
> + return;
> +
> + /* find */
> + spin_lock(&tree->lock);
> + entry = zswap_rb_search(&tree->rbroot, offset);
> + if (!entry) {
> + /* entry was flushed */
> + spin_unlock(&tree->lock);
> + return;
> + }
> +
> + /* remove from rbtree and lru */
> + rb_erase(&entry->rbnode, &tree->rbroot);
> + if (entry->lru.next != LIST_POISON1)
> + list_del(&entry->lru);
> + refcount = zswap_entry_put(entry);
> + spin_unlock(&tree->lock);
> + if (refcount) {
> + /* must be flushing */
> + return;
> + }
> +
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +}
> +
> +/* invalidates all pages for the given swap type */
> +static void zswap_frontswap_invalidate_area(unsigned type)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct rb_node *node, *next;
> + struct zswap_entry *entry;
> +
> + if (!tree)
When do we encounter this case?
> + return;
> +
> + /* walk the tree and free everything */
> + spin_lock(&tree->lock);
> + node = rb_first(&tree->rbroot);
> + while (node) {
> + entry = rb_entry(node, struct zswap_entry, rbnode);
> + zs_free(tree->pool, entry->handle);
> + next = rb_next(node);
> + zswap_entry_cache_free(entry);
> + node = next;
> + }
> + tree->rbroot = RB_ROOT;
> + INIT_LIST_HEAD(&tree->lru);
> + spin_unlock(&tree->lock);
> +}
> +
> +/* NOTE: this is called in atomic context from swapon and must not sleep */
> +static void zswap_frontswap_init(unsigned type)
> +{
> + struct zswap_tree *tree;
> +
> + tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
> + if (!tree)
> + goto err;
> + tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
> + if (!tree->pool)
> + goto freetree;
> + tree->rbroot = RB_ROOT;
> + INIT_LIST_HEAD(&tree->lru);
> + spin_lock_init(&tree->lock);
> + zswap_trees[type] = tree;
> + return;
> +
> +freetree:
> + kfree(tree);
> +err:
> + pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
> +}
> +
> +static struct frontswap_ops zswap_frontswap_ops = {
> + .store = zswap_frontswap_store,
> + .load = zswap_frontswap_load,
> + .invalidate_page = zswap_frontswap_invalidate_page,
> + .invalidate_area = zswap_frontswap_invalidate_area,
> + .init = zswap_frontswap_init
> +};
> +
> +/*********************************
> +* debugfs functions
> +**********************************/
> +#ifdef CONFIG_DEBUG_FS
> +#include <linux/debugfs.h>
> +
> +static struct dentry *zswap_debugfs_root;
> +
> +static int __init zswap_debugfs_init(void)
> +{
> + if (!debugfs_initialized())
> + return -ENODEV;
> +
> + zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
> + if (!zswap_debugfs_root)
> + return -ENOMEM;
> +
> + debugfs_create_u64("saved_by_flush", S_IRUGO,
> + zswap_debugfs_root, &zswap_saved_by_flush);
> + debugfs_create_u64("pool_limit_hit", S_IRUGO,
> + zswap_debugfs_root, &zswap_pool_limit_hit);
> + debugfs_create_u64("reject_flush_attempted", S_IRUGO,
> + zswap_debugfs_root, &zswap_flush_attempted);
> + debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_tmppage_fail);
> + debugfs_create_u64("reject_flush_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_flush_fail);
> + debugfs_create_u64("reject_zsmalloc_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_zsmalloc_fail);
> + debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_kmemcache_fail);
> + debugfs_create_u64("reject_compress_poor", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_compress_poor);
> + debugfs_create_u64("flushed_pages", S_IRUGO,
> + zswap_debugfs_root, &zswap_flushed_pages);
> + debugfs_create_u64("duplicate_entry", S_IRUGO,
> + zswap_debugfs_root, &zswap_duplicate_entry);
> + debugfs_create_atomic_t("pool_pages", S_IRUGO,
> + zswap_debugfs_root, &zswap_pool_pages);
> + debugfs_create_atomic_t("stored_pages", S_IRUGO,
> + zswap_debugfs_root, &zswap_stored_pages);
> + debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
> + zswap_debugfs_root, &zswap_outstanding_flushes);
> +
> + return 0;
> +}
> +
> +static void __exit zswap_debugfs_exit(void)
> +{
> + if (zswap_debugfs_root)
> + debugfs_remove_recursive(zswap_debugfs_root);
> +}
> +#else
> +static inline int __init zswap_debugfs_init(void)
> +{
> + return 0;
> +}
> +
> +static inline void __exit zswap_debugfs_exit(void) { }
> +#endif
> +
> +/*********************************
> +* module init and exit
> +**********************************/
> +static int __init init_zswap(void)
> +{
> + if (!zswap_enabled)
> + return 0;
> +
> + pr_info("loading zswap\n");
> + if (zswap_entry_cache_create()) {
> + pr_err("zswap: entry cache creation failed\n");
> + goto error;
> + }
> + if (zswap_page_pool_create()) {
> + pr_err("zswap: page pool initialization failed\n");
> + goto pagepoolfail;
> + }
> + if (zswap_tmppage_pool_create()) {
> + pr_err("zswap: workmem pool initialization failed\n");
> + goto tmppoolfail;
> + }
> + if (zswap_comp_init()) {
> + pr_err("zswap: compressor initialization failed\n");
> + goto compfail;
> + }
> + if (zswap_cpu_init()) {
> + pr_err("zswap: per-cpu initialization failed\n");
> + goto pcpufail;
> + }
> + frontswap_register_ops(&zswap_frontswap_ops);
> + if (zswap_debugfs_init())
> + pr_warn("zswap: debugfs initialization failed\n");
> + return 0;
> +pcpufail:
> + zswap_comp_exit();
> +compfail:
> + zswap_tmppage_pool_destroy();
> +tmppoolfail:
> + zswap_page_pool_destroy();
> +pagepoolfail:
> + zswap_entry_cache_destory();
> +error:
> + return -ENOMEM;
> +}
> +/* must be late so crypto has time to come up */
> +late_initcall(init_zswap);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
> +MODULE_DESCRIPTION("Compression backend for frontswap pages");
> --
> 1.7.9.5
>
> --
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> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
--
Kind regards,
Minchan Kim
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
@ 2013-01-29 6:27 ` Minchan Kim
0 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-29 6:27 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
First feeling is it's simple and nice approach.
Although we have some problems to decide policy, it could solve by later patch
so I hope we make basic infrasture more solid by lots of comment.
There are two things to review hard.
1. data structure life - when any data structure is died by whom?
Please write down it in changelog or header of zswap.c
2. Flush routine - I hope it would be nice to separate it as another
incremental patches if it is possible. If it's impossible, let's add
lots of words.
On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
> zswap is a thin compression backend for frontswap. It receives
> pages from frontswap and attempts to store them in a compressed
> memory pool, resulting in an effective partial memory reclaim and
> dramatically reduced swap device I/O.
>
> Additional, in most cases, pages can be retrieved from this
> compressed store much more quickly than reading from tradition
> swap devices resulting in faster performance for many workloads.
>
> This patch adds the zswap driver to mm/
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> ---
> mm/Kconfig | 15 +
> mm/Makefile | 1 +
> mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 1089 insertions(+)
> create mode 100644 mm/zswap.c
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 278e3ab..14b9acb 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -446,3 +446,18 @@ config FRONTSWAP
> and swap data is stored as normal on the matching swap device.
>
> If unsure, say Y to enable frontswap.
> +
> +config ZSWAP
> + bool "In-kernel swap page compression"
> + depends on FRONTSWAP && CRYPTO
Couldn't we support CRYPTO optionally?
> + select CRYPTO_LZO
> + select ZSMALLOC
> + default n
> + help
> + Zswap is a backend for the frontswap mechanism in the VMM.
> + It receives pages from frontswap and attempts to store them
> + in a compressed memory pool, resulting in an effective
> + partial memory reclaim. In addition, pages and be retrieved
> + from this compressed store much faster than most tradition
> + swap devices resulting in reduced I/O and faster performance
> + for many workloads.
> diff --git a/mm/Makefile b/mm/Makefile
> index 3a46287..1b1ed5c 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
> obj-$(CONFIG_BOUNCE) += bounce.o
> obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
> obj-$(CONFIG_FRONTSWAP) += frontswap.o
> +obj-$(CONFIG_ZSWAP) += zswap.o
> obj-$(CONFIG_HAS_DMA) += dmapool.o
> obj-$(CONFIG_HUGETLBFS) += hugetlb.o
> obj-$(CONFIG_NUMA) += mempolicy.o
> diff --git a/mm/zswap.c b/mm/zswap.c
> new file mode 100644
> index 0000000..050b6db
> --- /dev/null
> +++ b/mm/zswap.c
> @@ -0,0 +1,1073 @@
> +/*
> + * zswap-drv.c - zswap driver file
> + *
> + * zswap is a backend for frontswap that takes pages that are in the
> + * process of being swapped out and attempts to compress them and store
> + * them in a RAM-based memory pool. This results in a significant I/O
> + * reduction on the real swap device and, in the case of a slow swap
> + * device, can also improve workload performance.
> + *
> + * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> +*/
> +
> +#include <linux/module.h>
> +#include <linux/cpu.h>
> +#include <linux/highmem.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +#include <linux/atomic.h>
> +#include <linux/frontswap.h>
> +#include <linux/rbtree.h>
> +#include <linux/swap.h>
> +#include <linux/crypto.h>
> +#include <linux/mempool.h>
> +#include <linux/zsmalloc.h>
> +
> +#include <linux/mm_types.h>
> +#include <linux/page-flags.h>
> +#include <linux/swapops.h>
> +#include <linux/writeback.h>
> +#include <linux/pagemap.h>
> +
> +/*********************************
> +* statistics
> +**********************************/
> +/* Number of memory pages used by the compressed pool */
> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
> +/* The number of compressed pages currently stored in zswap */
> +static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
> +/* The number of outstanding pages awaiting writeback */
> +static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
> +
> +/*
> + * The statistics below are not protected from concurrent access for
> + * performance reasons so they may not be a 100% accurate. However,
> + * the do provide useful information on roughly how many times a
> + * certain event is occurring.
> +*/
> +static u64 zswap_flushed_pages;
> +static u64 zswap_reject_compress_poor;
> +static u64 zswap_flush_attempted;
> +static u64 zswap_reject_tmppage_fail;
> +static u64 zswap_reject_flush_fail;
> +static u64 zswap_reject_zsmalloc_fail;
> +static u64 zswap_reject_kmemcache_fail;
> +static u64 zswap_saved_by_flush;
> +static u64 zswap_duplicate_entry;
> +
> +/*********************************
> +* tunables
> +**********************************/
> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
> +static bool zswap_enabled;
> +module_param_named(enabled, zswap_enabled, bool, 0);
It seems default is disable at the moment?
> +
> +/* Compressor to be used by zswap (fixed at boot for now) */
> +#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> +module_param_named(compressor, zswap_compressor, charp, 0);
> +
> +/* The maximum percentage of memory that the compressed pool can occupy */
> +static unsigned int zswap_max_pool_percent = 20;
> +module_param_named(max_pool_percent,
> + zswap_max_pool_percent, uint, 0644);
> +
> +/*
> + * Maximum compression ratio, as as percentage, for an acceptable
> + * compressed page. Any pages that do not compress by at least
> + * this ratio will be rejected.
> +*/
> +static unsigned int zswap_max_compression_ratio = 80;
> +module_param_named(max_compression_ratio,
> + zswap_max_compression_ratio, uint, 0644);
> +
> +/*
> + * Maximum number of outstanding flushes allowed at any given time.
> + * This is to prevent decompressing an unbounded number of compressed
> + * pages into the swap cache all at once, and to help with writeback
> + * congestion.
> +*/
> +#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
> +
> +/*********************************
> +* compression functions
> +**********************************/
> +/* per-cpu compression transforms */
> +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
> +
> +enum comp_op {
> + ZSWAP_COMPOP_COMPRESS,
> + ZSWAP_COMPOP_DECOMPRESS
> +};
> +
> +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
> + u8 *dst, unsigned int *dlen)
> +{
> + struct crypto_comp *tfm;
> + int ret;
> +
> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
> + switch (op) {
> + case ZSWAP_COMPOP_COMPRESS:
> + ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
> + break;
> + case ZSWAP_COMPOP_DECOMPRESS:
> + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
> + break;
> + default:
> + ret = -EINVAL;
> + }
> +
> + put_cpu();
> + return ret;
> +}
> +
> +static int __init zswap_comp_init(void)
> +{
> + if (!crypto_has_comp(zswap_compressor, 0, 0)) {
> + pr_info("zswap: %s compressor not available\n",
> + zswap_compressor);
> + /* fall back to default compressor */
> + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> + if (!crypto_has_comp(zswap_compressor, 0, 0))
> + /* can't even load the default compressor */
> + return -ENODEV;
> + }
> + pr_info("zswap: using %s compressor\n", zswap_compressor);
> +
> + /* alloc percpu transforms */
> + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
> + if (!zswap_comp_pcpu_tfms)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +static void zswap_comp_exit(void)
> +{
> + /* free percpu transforms */
> + if (zswap_comp_pcpu_tfms)
> + free_percpu(zswap_comp_pcpu_tfms);
> +}
> +
> +/*********************************
> +* data structures
> +**********************************/
> +struct zswap_entry {
> + struct rb_node rbnode;
> + struct list_head lru;
> + int refcount;
> + unsigned type;
> + pgoff_t offset;
> + unsigned long handle;
> + unsigned int length;
> +};
> +
> +/*
> + * The tree lock in the zswap_tree struct protects a few things:
> + * - the rbtree
> + * - the lru list
> + * - the refcount field of each entry in the tree
> + */
> +struct zswap_tree {
> + struct rb_root rbroot;
> + struct list_head lru;
> + spinlock_t lock;
> + struct zs_pool *pool;
> +};
> +
> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
> +
> +/*********************************
> +* zswap entry functions
> +**********************************/
> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
> +static struct kmem_cache *zswap_entry_cache;
> +
> +static inline int zswap_entry_cache_create(void)
> +{
> + zswap_entry_cache =
> + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
> + sizeof(struct zswap_entry), 0, 0, NULL);
> + return (zswap_entry_cache == NULL);
> +}
> +
> +static inline void zswap_entry_cache_destory(void)
> +{
> + kmem_cache_destroy(zswap_entry_cache);
> +}
> +
> +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
> +{
> + struct zswap_entry *entry;
> + entry = kmem_cache_alloc(zswap_entry_cache, gfp);
> + if (!entry)
> + return NULL;
> + INIT_LIST_HEAD(&entry->lru);
> + entry->refcount = 1;
> + return entry;
> +}
> +
> +static inline void zswap_entry_cache_free(struct zswap_entry *entry)
> +{
> + kmem_cache_free(zswap_entry_cache, entry);
> +}
> +
> +static inline void zswap_entry_get(struct zswap_entry *entry)
> +{
> + entry->refcount++;
> +}
> +
> +static inline int zswap_entry_put(struct zswap_entry *entry)
> +{
> + entry->refcount--;
> + return entry->refcount;
> +}
> +
> +/*********************************
> +* rbtree functions
> +**********************************/
> +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
> +{
> + struct rb_node *node = root->rb_node;
> + struct zswap_entry *entry;
> +
> + while (node) {
> + entry = rb_entry(node, struct zswap_entry, rbnode);
> + if (entry->offset > offset)
> + node = node->rb_left;
> + else if (entry->offset < offset)
> + node = node->rb_right;
> + else
> + return entry;
> + }
> + return NULL;
> +}
> +
> +/*
> + * In the case that a entry with the same offset is found, it a pointer to
> + * the existing entry is stored in dupentry and the function returns -EEXIST
> +*/
> +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
> + struct zswap_entry **dupentry)
> +{
> + struct rb_node **link = &root->rb_node, *parent = NULL;
> + struct zswap_entry *myentry;
> +
> + while (*link) {
> + parent = *link;
> + myentry = rb_entry(parent, struct zswap_entry, rbnode);
> + if (myentry->offset > entry->offset)
> + link = &(*link)->rb_left;
> + else if (myentry->offset < entry->offset)
> + link = &(*link)->rb_right;
> + else {
> + *dupentry = myentry;
> + return -EEXIST;
> + }
> + }
> + rb_link_node(&entry->rbnode, parent, link);
> + rb_insert_color(&entry->rbnode, root);
> + return 0;
> +}
> +
> +/*********************************
> +* per-cpu code
> +**********************************/
> +static DEFINE_PER_CPU(u8 *, zswap_dstmem);
> +
> +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
> +{
> + struct crypto_comp *tfm;
> + u8 *dst;
> +
> + switch (action) {
> + case CPU_UP_PREPARE:
> + tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
> + if (IS_ERR(tfm)) {
> + pr_err("zswap: can't allocate compressor transform\n");
> + return NOTIFY_BAD;
> + }
> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
> + dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
> + if (!dst) {
> + pr_err("zswap: can't allocate compressor buffer\n");
> + crypto_free_comp(tfm);
> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> + return NOTIFY_BAD;
> + }
> + per_cpu(zswap_dstmem, cpu) = dst;
> + break;
> + case CPU_DEAD:
> + case CPU_UP_CANCELED:
> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
> + if (tfm) {
> + crypto_free_comp(tfm);
> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> + }
> + dst = per_cpu(zswap_dstmem, cpu);
> + if (dst) {
> + free_pages((unsigned long)dst, 1);
> + per_cpu(zswap_dstmem, cpu) = NULL;
> + }
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> +static int zswap_cpu_notifier(struct notifier_block *nb,
> + unsigned long action, void *pcpu)
> +{
> + unsigned long cpu = (unsigned long)pcpu;
> + return __zswap_cpu_notifier(action, cpu);
> +}
> +
> +static struct notifier_block zswap_cpu_notifier_block = {
> + .notifier_call = zswap_cpu_notifier
> +};
> +
> +static int zswap_cpu_init(void)
> +{
> + unsigned long cpu;
> +
> + get_online_cpus();
> + for_each_online_cpu(cpu)
> + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
> + goto cleanup;
> + register_cpu_notifier(&zswap_cpu_notifier_block);
> + put_online_cpus();
> + return 0;
> +
> +cleanup:
> + for_each_online_cpu(cpu)
> + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
> + put_online_cpus();
> + return -ENOMEM;
> +}
> +
> +/*********************************
> +* zsmalloc callbacks
> +**********************************/
> +static mempool_t *zswap_page_pool;
> +
> +static u64 zswap_pool_limit_hit;
> +
> +static inline unsigned int zswap_max_pool_pages(void)
> +{
> + return zswap_max_pool_percent * totalram_pages / 100;
> +}
> +
> +static inline int zswap_page_pool_create(void)
> +{
> + zswap_page_pool = mempool_create_page_pool(256, 0);
Could you write down why you select pool to 256?
If you have a plan, please write down it as TODO.
I think it could be a function of zswap_max_pool_pages with min/max.
Another question.
What's the benefit of using mempool for zsmalloc?
As you know, zsmalloc doesn't use mempool as default.
I guess you see some benefit. if so, zram could be changed.
If we can change zsmalloc's default scheme to use mempool,
all of customer of zsmalloc could be enhanced, too.
> + if (!zswap_page_pool)
> + return -ENOMEM;
> + return 0;
> +}
> +
> +static inline void zswap_page_pool_destroy(void)
> +{
> + mempool_destroy(zswap_page_pool);
> +}
> +
> +static struct page *zswap_alloc_page(gfp_t flags)
> +{
> + struct page *page;
> +
> + if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
> + zswap_pool_limit_hit++;
> + return NULL;
> + }
> + page = mempool_alloc(zswap_page_pool, flags);
> + if (page)
> + atomic_inc(&zswap_pool_pages);
> + return page;
> +}
> +
> +static void zswap_free_page(struct page *page)
> +{
> + mempool_free(page, zswap_page_pool);
> + atomic_dec(&zswap_pool_pages);
Nit.
By semantic, free function can receive NULL argument so
atomic_dec would be nice to check it before decreasing count.
> +}
> +
> +static struct zs_ops zswap_zs_ops = {
> + .alloc = zswap_alloc_page,
> + .free = zswap_free_page
> +};
> +
> +/*********************************
> +* flush code
> +**********************************/
> +static void zswap_end_swap_write(struct bio *bio, int err)
> +{
> + end_swap_bio_write(bio, err);
> + atomic_dec(&zswap_outstanding_flushes);
> + zswap_flushed_pages++;
> +}
> +
> +/*
> + * zswap_get_swap_cache_page
> + *
> + * This is an adaption of read_swap_cache_async()
> + *
> + * If success, page is returned in retpage
> + * Returns 0 if page was already in the swap cache, page is not locked
> + * Returns 1 if the new page needs to be populated, page is locked
> + */
> +static int zswap_get_swap_cache_page(swp_entry_t entry,
> + struct page **retpage)
> +{
> + struct page *found_page, *new_page = NULL;
> + int err;
> +
> + *retpage = NULL;
> + do {
> + /*
> + * First check the swap cache. Since this is normally
> + * called after lookup_swap_cache() failed, re-calling
> + * that would confuse statistics.
> + */
> + found_page = find_get_page(&swapper_space, entry.val);
> + if (found_page)
> + break;
> +
> + /*
> + * Get a new page to read into from swap.
> + */
> + if (!new_page) {
> + new_page = alloc_page(GFP_KERNEL);
> + if (!new_page)
> + break; /* Out of memory */
> + }
> +
> + /*
> + * call radix_tree_preload() while we can wait.
> + */
> + err = radix_tree_preload(GFP_KERNEL);
> + if (err)
> + break;
> +
> + /*
> + * Swap entry may have been freed since our caller observed it.
> + */
> + err = swapcache_prepare(entry);
> + if (err == -EEXIST) { /* seems racy */
> + radix_tree_preload_end();
> + continue;
> + }
> + if (err) { /* swp entry is obsolete ? */
> + radix_tree_preload_end();
> + break;
> + }
> +
> + /* May fail (-ENOMEM) if radix-tree node allocation failed. */
> + __set_page_locked(new_page);
> + SetPageSwapBacked(new_page);
> + err = __add_to_swap_cache(new_page, entry);
> + if (likely(!err)) {
> + radix_tree_preload_end();
> + lru_cache_add_anon(new_page);
> + *retpage = new_page;
> + return 1;
> + }
> + radix_tree_preload_end();
> + ClearPageSwapBacked(new_page);
> + __clear_page_locked(new_page);
> + /*
> + * add_to_swap_cache() doesn't return -EEXIST, so we can safely
> + * clear SWAP_HAS_CACHE flag.
> + */
> + swapcache_free(entry, NULL);
> + } while (err != -ENOMEM);
> +
> + if (new_page)
> + page_cache_release(new_page);
> + if (!found_page)
> + return -ENOMEM;
> + *retpage = found_page;
> + return 0;
> +}
> +
> +static int zswap_flush_entry(struct zswap_entry *entry)
> +{
> + unsigned long type = entry->type;
> + struct zswap_tree *tree = zswap_trees[type];
> + struct page *page;
> + swp_entry_t swpentry;
> + u8 *src, *dst;
> + unsigned int dlen;
> + int ret, refcount;
> + struct writeback_control wbc = {
> + .sync_mode = WB_SYNC_NONE,
> + };
> +
> + /* get/allocate page in the swap cache */
> + swpentry = swp_entry(type, entry->offset);
> + ret = zswap_get_swap_cache_page(swpentry, &page);
> + if (ret < 0)
> + return ret;
> + else if (ret) {
> + /* decompress */
> + dlen = PAGE_SIZE;
> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
> + dst = kmap_atomic(page);
> + ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
> + dst, &dlen);
> + kunmap_atomic(dst);
> + zs_unmap_object(tree->pool, entry->handle);
> + BUG_ON(ret);
> + BUG_ON(dlen != PAGE_SIZE);
> + SetPageUptodate(page);
> + } else {
> + /* page is already in the swap cache, ignore for now */
> + spin_lock(&tree->lock);
> + refcount = zswap_entry_put(entry);
> + spin_unlock(&tree->lock);
> +
> + if (likely(refcount))
> + return 0;
> +
> + /* if the refcount is zero, invalidate must have come in */
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +
> + return 0;
> + }
> +
> + /* start writeback */
> + SetPageReclaim(page);
> + /*
> + * Return value is ignored here because it doesn't change anything
> + * for us. Page is returned unlocked.
> + */
> + (void)__swap_writepage(page, &wbc, zswap_end_swap_write);
> + page_cache_release(page);
> + atomic_inc(&zswap_outstanding_flushes);
> +
> + /* remove */
> + spin_lock(&tree->lock);
> + refcount = zswap_entry_put(entry);
> + if (refcount > 1) {
> + /* load in progress, load will free */
> + spin_unlock(&tree->lock);
> + return 0;
> + }
> + if (refcount == 1)
> + /* no invalidate yet, remove from rbtree */
> + rb_erase(&entry->rbnode, &tree->rbroot);
> + spin_unlock(&tree->lock);
> +
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +
> + return 0;
> +}
> +
> +static void zswap_flush_entries(unsigned type, int nr)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry;
> + int i, ret;
> +
> +/*
> + * This limits is arbitrary for now until a better
> + * policy can be implemented. This is so we don't
> + * eat all of RAM decompressing pages for writeback.
> + */
> + if (atomic_read(&zswap_outstanding_flushes) >
> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
> + return;
> +
> + for (i = 0; i < nr; i++) {
> + /* dequeue from lru */
> + spin_lock(&tree->lock);
> + if (list_empty(&tree->lru)) {
> + spin_unlock(&tree->lock);
> + break;
> + }
> + entry = list_first_entry(&tree->lru,
> + struct zswap_entry, lru);
> + list_del(&entry->lru);
> + zswap_entry_get(entry);
> + spin_unlock(&tree->lock);
> + ret = zswap_flush_entry(entry);
> + if (ret) {
> + /* put back on the lru */
> + spin_lock(&tree->lock);
> + list_add(&entry->lru, &tree->lru);
> + spin_unlock(&tree->lock);
> + } else {
> + if (atomic_read(&zswap_outstanding_flushes) >
> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
> + break;
> + }
> + }
> +}
The flush part complexity is very high so we needs careful review.
I hope you can make the patch step by step from ugly approach to smart one.
It helps reviewers much.
If it isn't easy, I will review as it is.
> +
> +/*******************************************
> +* page pool for temporary compression result
> +********************************************/
> +#define ZSWAP_TMPPAGE_POOL_PAGES 16
> +static LIST_HEAD(zswap_tmppage_list);
> +static DEFINE_SPINLOCK(zswap_tmppage_lock);
> +
> +static void zswap_tmppage_pool_destroy(void)
> +{
> + struct page *page, *tmppage;
> +
> + spin_lock(&zswap_tmppage_lock);
> + list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
> + list_del(&page->lru);
> + __free_pages(page, 1);
> + }
> + spin_unlock(&zswap_tmppage_lock);
> +}
> +
> +static int zswap_tmppage_pool_create(void)
> +{
> + int i;
> + struct page *page;
> +
> + for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
> + page = alloc_pages(GFP_KERNEL, 1);
> + if (!page) {
> + zswap_tmppage_pool_destroy();
> + return -ENOMEM;
> + }
> + spin_lock(&zswap_tmppage_lock);
> + list_add(&page->lru, &zswap_tmppage_list);
> + spin_unlock(&zswap_tmppage_lock);
> + }
> + return 0;
> +}
> +
> +static inline struct page *zswap_tmppage_alloc(void)
> +{
> + struct page *page;
> +
> + spin_lock(&zswap_tmppage_lock);
> + if (list_empty(&zswap_tmppage_list)) {
> + spin_unlock(&zswap_tmppage_lock);
> + return NULL;
> + }
> + page = list_first_entry(&zswap_tmppage_list, struct page, lru);
> + list_del(&page->lru);
> + spin_unlock(&zswap_tmppage_lock);
> + return page;
> +}
> +
> +static inline void zswap_tmppage_free(struct page *page)
> +{
> + spin_lock(&zswap_tmppage_lock);
> + list_add(&page->lru, &zswap_tmppage_list);
> + spin_unlock(&zswap_tmppage_lock);
> +}
> +
> +/*********************************
> +* frontswap hooks
> +**********************************/
> +/* attempts to compress and store an single page */
> +static int zswap_frontswap_store(unsigned type, pgoff_t offset, struct page *page)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry, *dupentry;
> + int ret;
> + unsigned int dlen = PAGE_SIZE;
> + unsigned long handle;
> + char *buf;
> + u8 *src, *dst, *tmpdst;
> + struct page *tmppage;
> + bool flush_attempted = 0;
> +
> + if (!tree) {
> + ret = -ENODEV;
> + goto reject;
> + }
> +
> + /* compress */
> + dst = get_cpu_var(zswap_dstmem);
> + src = kmap_atomic(page);
> + ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
> + kunmap_atomic(src);
> + if (ret) {
> + ret = -EINVAL;
> + goto freepage;
> + }
> + if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
> + zswap_reject_compress_poor++;
> + ret = -E2BIG;
> + goto freepage;
> + }
> +
> + /* store */
> + handle = zs_malloc(tree->pool, dlen,
> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
> + __GFP_NOWARN);
> + if (!handle) {
> + zswap_flush_attempted++;
> + /*
> + * Copy compressed buffer out of per-cpu storage so
> + * we can re-enable preemption.
> + */
> + tmppage = zswap_tmppage_alloc();
> + if (!tmppage) {
> + zswap_reject_tmppage_fail++;
> + ret = -ENOMEM;
> + goto freepage;
> + }
> + flush_attempted = 1;
> + tmpdst = page_address(tmppage);
> + memcpy(tmpdst, dst, dlen);
> + dst = tmpdst;
> + put_cpu_var(zswap_dstmem);
> +
> + /* try to free up some space */
> + /* TODO: replace with more targeted policy */
> + zswap_flush_entries(type, 16);
> + /* try again, allowing wait */
> + handle = zs_malloc(tree->pool, dlen,
> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
> + __GFP_NOWARN);
> + if (!handle) {
> + /* still no space, fail */
> + zswap_reject_zsmalloc_fail++;
> + ret = -ENOMEM;
> + goto freepage;
> + }
> + zswap_saved_by_flush++;
> + }
> +
> + buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
> + memcpy(buf, dst, dlen);
> + zs_unmap_object(tree->pool, handle);
> + if (flush_attempted)
> + zswap_tmppage_free(tmppage);
> + else
> + put_cpu_var(zswap_dstmem);
> +
> + /* allocate entry */
> + entry = zswap_entry_cache_alloc(GFP_KERNEL);
> + if (!entry) {
zs_free
> + zswap_reject_kmemcache_fail++;
> + ret = -ENOMEM;
> + goto reject;
> + }
> +
> + /* populate entry */
> + entry->type = type;
> + entry->offset = offset;
> + entry->handle = handle;
> + entry->length = dlen;
> +
> + /* map */
> + spin_lock(&tree->lock);
> + do {
> + ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
Could you describe why existing entry could be there?
IIUC, it is caused by delayed swap slot free of VM. Right?
Anyway, it would be nice to add comment about it.
> + if (ret == -EEXIST) {
> + zswap_duplicate_entry++;
> + /* remove from rbtree and lru */
> + rb_erase(&dupentry->rbnode, &tree->rbroot);
> + if (dupentry->lru.next != LIST_POISON1)
Why do we need this check? Is there any case entry isn't linked at LRU list?
Because you already removed it in load part. Right?
Let's add comment about that. And let's not dependent on LIST_POISON1 of
list util but use explicit zswap's one.
> + list_del(&dupentry->lru);
> + if (!zswap_entry_put(dupentry)) {
> + /* free */
> + zs_free(tree->pool, dupentry->handle);
> + zswap_entry_cache_free(dupentry);
> + atomic_dec(&zswap_stored_pages);
> + }
> + }
> + } while (ret == -EEXIST);
> + list_add_tail(&entry->lru, &tree->lru);
> + spin_unlock(&tree->lock);
> +
> + /* update stats */
> + atomic_inc(&zswap_stored_pages);
> +
> + return 0;
> +
> +freepage:
> + if (flush_attempted)
> + zswap_tmppage_free(tmppage);
> + else
> + put_cpu_var(zswap_dstmem);
> +reject:
> + return ret;
> +}
> +
> +/*
> + * returns 0 if the page was successfully decompressed
> + * return -1 on entry not found or error
> +*/
> +static int zswap_frontswap_load(unsigned type, pgoff_t offset, struct page *page)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry;
> + u8 *src, *dst;
> + unsigned int dlen;
> + int refcount;
> +
> + /* find */
> + spin_lock(&tree->lock);
> + entry = zswap_rb_search(&tree->rbroot, offset);
> + if (!entry) {
> + /* entry was flushed */
> + spin_unlock(&tree->lock);
> + return -1;
> + }
> + zswap_entry_get(entry);
> +
> + /* remove from lru */
> + if (entry->lru.next != LIST_POISON1)
When do we encounter this case?
By racing with flush?
Need comment, too.
> + list_del(&entry->lru);
> + spin_unlock(&tree->lock);
> +
> + /* decompress */
> + dlen = PAGE_SIZE;
> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
> + dst = kmap_atomic(page);
> + zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
> + dst, &dlen);
> + kunmap_atomic(dst);
> + zs_unmap_object(tree->pool, entry->handle);
> +
> + spin_lock(&tree->lock);
> + refcount = zswap_entry_put(entry);
> + if (likely(refcount)) {
> + list_add_tail(&entry->lru, &tree->lru);
> + spin_unlock(&tree->lock);
> + return 0;
> + }
> + spin_unlock(&tree->lock);
> +
> + /*
> + * We don't have to unlink from the rbtree because zswap_flush_entry()
> + * or zswap_frontswap_invalidate page() has already done this for us if we
> + * are the last reference.
> + */
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +
> + return 0;
> +}
> +
> +/* invalidates a single page */
> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct zswap_entry *entry;
> + int refcount;
> +
> + if (!tree)
When do we encounter this case?
> + return;
> +
> + /* find */
> + spin_lock(&tree->lock);
> + entry = zswap_rb_search(&tree->rbroot, offset);
> + if (!entry) {
> + /* entry was flushed */
> + spin_unlock(&tree->lock);
> + return;
> + }
> +
> + /* remove from rbtree and lru */
> + rb_erase(&entry->rbnode, &tree->rbroot);
> + if (entry->lru.next != LIST_POISON1)
> + list_del(&entry->lru);
> + refcount = zswap_entry_put(entry);
> + spin_unlock(&tree->lock);
> + if (refcount) {
> + /* must be flushing */
> + return;
> + }
> +
> + /* free */
> + zs_free(tree->pool, entry->handle);
> + zswap_entry_cache_free(entry);
> + atomic_dec(&zswap_stored_pages);
> +}
> +
> +/* invalidates all pages for the given swap type */
> +static void zswap_frontswap_invalidate_area(unsigned type)
> +{
> + struct zswap_tree *tree = zswap_trees[type];
> + struct rb_node *node, *next;
> + struct zswap_entry *entry;
> +
> + if (!tree)
When do we encounter this case?
> + return;
> +
> + /* walk the tree and free everything */
> + spin_lock(&tree->lock);
> + node = rb_first(&tree->rbroot);
> + while (node) {
> + entry = rb_entry(node, struct zswap_entry, rbnode);
> + zs_free(tree->pool, entry->handle);
> + next = rb_next(node);
> + zswap_entry_cache_free(entry);
> + node = next;
> + }
> + tree->rbroot = RB_ROOT;
> + INIT_LIST_HEAD(&tree->lru);
> + spin_unlock(&tree->lock);
> +}
> +
> +/* NOTE: this is called in atomic context from swapon and must not sleep */
> +static void zswap_frontswap_init(unsigned type)
> +{
> + struct zswap_tree *tree;
> +
> + tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
> + if (!tree)
> + goto err;
> + tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
> + if (!tree->pool)
> + goto freetree;
> + tree->rbroot = RB_ROOT;
> + INIT_LIST_HEAD(&tree->lru);
> + spin_lock_init(&tree->lock);
> + zswap_trees[type] = tree;
> + return;
> +
> +freetree:
> + kfree(tree);
> +err:
> + pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
> +}
> +
> +static struct frontswap_ops zswap_frontswap_ops = {
> + .store = zswap_frontswap_store,
> + .load = zswap_frontswap_load,
> + .invalidate_page = zswap_frontswap_invalidate_page,
> + .invalidate_area = zswap_frontswap_invalidate_area,
> + .init = zswap_frontswap_init
> +};
> +
> +/*********************************
> +* debugfs functions
> +**********************************/
> +#ifdef CONFIG_DEBUG_FS
> +#include <linux/debugfs.h>
> +
> +static struct dentry *zswap_debugfs_root;
> +
> +static int __init zswap_debugfs_init(void)
> +{
> + if (!debugfs_initialized())
> + return -ENODEV;
> +
> + zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
> + if (!zswap_debugfs_root)
> + return -ENOMEM;
> +
> + debugfs_create_u64("saved_by_flush", S_IRUGO,
> + zswap_debugfs_root, &zswap_saved_by_flush);
> + debugfs_create_u64("pool_limit_hit", S_IRUGO,
> + zswap_debugfs_root, &zswap_pool_limit_hit);
> + debugfs_create_u64("reject_flush_attempted", S_IRUGO,
> + zswap_debugfs_root, &zswap_flush_attempted);
> + debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_tmppage_fail);
> + debugfs_create_u64("reject_flush_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_flush_fail);
> + debugfs_create_u64("reject_zsmalloc_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_zsmalloc_fail);
> + debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_kmemcache_fail);
> + debugfs_create_u64("reject_compress_poor", S_IRUGO,
> + zswap_debugfs_root, &zswap_reject_compress_poor);
> + debugfs_create_u64("flushed_pages", S_IRUGO,
> + zswap_debugfs_root, &zswap_flushed_pages);
> + debugfs_create_u64("duplicate_entry", S_IRUGO,
> + zswap_debugfs_root, &zswap_duplicate_entry);
> + debugfs_create_atomic_t("pool_pages", S_IRUGO,
> + zswap_debugfs_root, &zswap_pool_pages);
> + debugfs_create_atomic_t("stored_pages", S_IRUGO,
> + zswap_debugfs_root, &zswap_stored_pages);
> + debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
> + zswap_debugfs_root, &zswap_outstanding_flushes);
> +
> + return 0;
> +}
> +
> +static void __exit zswap_debugfs_exit(void)
> +{
> + if (zswap_debugfs_root)
> + debugfs_remove_recursive(zswap_debugfs_root);
> +}
> +#else
> +static inline int __init zswap_debugfs_init(void)
> +{
> + return 0;
> +}
> +
> +static inline void __exit zswap_debugfs_exit(void) { }
> +#endif
> +
> +/*********************************
> +* module init and exit
> +**********************************/
> +static int __init init_zswap(void)
> +{
> + if (!zswap_enabled)
> + return 0;
> +
> + pr_info("loading zswap\n");
> + if (zswap_entry_cache_create()) {
> + pr_err("zswap: entry cache creation failed\n");
> + goto error;
> + }
> + if (zswap_page_pool_create()) {
> + pr_err("zswap: page pool initialization failed\n");
> + goto pagepoolfail;
> + }
> + if (zswap_tmppage_pool_create()) {
> + pr_err("zswap: workmem pool initialization failed\n");
> + goto tmppoolfail;
> + }
> + if (zswap_comp_init()) {
> + pr_err("zswap: compressor initialization failed\n");
> + goto compfail;
> + }
> + if (zswap_cpu_init()) {
> + pr_err("zswap: per-cpu initialization failed\n");
> + goto pcpufail;
> + }
> + frontswap_register_ops(&zswap_frontswap_ops);
> + if (zswap_debugfs_init())
> + pr_warn("zswap: debugfs initialization failed\n");
> + return 0;
> +pcpufail:
> + zswap_comp_exit();
> +compfail:
> + zswap_tmppage_pool_destroy();
> +tmppoolfail:
> + zswap_page_pool_destroy();
> +pagepoolfail:
> + zswap_entry_cache_destory();
> +error:
> + return -ENOMEM;
> +}
> +/* must be late so crypto has time to come up */
> +late_initcall(init_zswap);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
> +MODULE_DESCRIPTION("Compression backend for frontswap pages");
> --
> 1.7.9.5
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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--
Kind regards,
Minchan Kim
--
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
2013-01-29 6:27 ` Minchan Kim
@ 2013-01-29 17:26 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-29 17:26 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On 01/29/2013 12:27 AM, Minchan Kim wrote:
> First feeling is it's simple and nice approach.
> Although we have some problems to decide policy, it could solve by later patch
> so I hope we make basic infrasture more solid by lots of comment.
Thanks very much for the review!
>
> There are two things to review hard.
>
> 1. data structure life - when any data structure is died by whom?
> Please write down it in changelog or header of zswap.c
>
> 2. Flush routine - I hope it would be nice to separate it as another
> incremental patches if it is possible. If it's impossible, let's add
> lots of words.
It seems like it would be difficult to break the flushing
functionality into it's own patch, but I can start the process and
see. As long as people keep in mind that some of the design rationale
in the version without the flush code is dictated by the addition of
the flush code.
But yes, more comments.
> On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
>> zswap is a thin compression backend for frontswap. It receives
>> pages from frontswap and attempts to store them in a compressed
>> memory pool, resulting in an effective partial memory reclaim and
>> dramatically reduced swap device I/O.
>>
>> Additional, in most cases, pages can be retrieved from this
>> compressed store much more quickly than reading from tradition
>> swap devices resulting in faster performance for many workloads.
>>
>> This patch adds the zswap driver to mm/
>>
>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>> ---
>> mm/Kconfig | 15 +
>> mm/Makefile | 1 +
>> mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 1089 insertions(+)
>> create mode 100644 mm/zswap.c
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 278e3ab..14b9acb 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -446,3 +446,18 @@ config FRONTSWAP
>> and swap data is stored as normal on the matching swap device.
>>
>> If unsure, say Y to enable frontswap.
>> +
>> +config ZSWAP
>> + bool "In-kernel swap page compression"
>> + depends on FRONTSWAP && CRYPTO
>
> Couldn't we support CRYPTO optionally?
No. zswap depends on the cryptographic API for access to the
compression modules.
>
>> + select CRYPTO_LZO
>> + select ZSMALLOC
>> + default n
>> + help
>> + Zswap is a backend for the frontswap mechanism in the VMM.
>> + It receives pages from frontswap and attempts to store them
>> + in a compressed memory pool, resulting in an effective
>> + partial memory reclaim. In addition, pages and be retrieved
>> + from this compressed store much faster than most tradition
>> + swap devices resulting in reduced I/O and faster performance
>> + for many workloads.
>> diff --git a/mm/Makefile b/mm/Makefile
>> index 3a46287..1b1ed5c 100644
>> --- a/mm/Makefile
>> +++ b/mm/Makefile
>> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
>> obj-$(CONFIG_BOUNCE) += bounce.o
>> obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
>> obj-$(CONFIG_FRONTSWAP) += frontswap.o
>> +obj-$(CONFIG_ZSWAP) += zswap.o
>> obj-$(CONFIG_HAS_DMA) += dmapool.o
>> obj-$(CONFIG_HUGETLBFS) += hugetlb.o
>> obj-$(CONFIG_NUMA) += mempolicy.o
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> new file mode 100644
>> index 0000000..050b6db
>> --- /dev/null
>> +++ b/mm/zswap.c
>> @@ -0,0 +1,1073 @@
>> +/*
>> + * zswap-drv.c - zswap driver file
>> + *
>> + * zswap is a backend for frontswap that takes pages that are in the
>> + * process of being swapped out and attempts to compress them and store
>> + * them in a RAM-based memory pool. This results in a significant I/O
>> + * reduction on the real swap device and, in the case of a slow swap
>> + * device, can also improve workload performance.
>> + *
>> + * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
>> + *
>> + * This program is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU General Public License
>> + * as published by the Free Software Foundation; either version 2
>> + * of the License, or (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> + * GNU General Public License for more details.
>> +*/
>> +
>> +#include <linux/module.h>
>> +#include <linux/cpu.h>
>> +#include <linux/highmem.h>
>> +#include <linux/slab.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/types.h>
>> +#include <linux/atomic.h>
>> +#include <linux/frontswap.h>
>> +#include <linux/rbtree.h>
>> +#include <linux/swap.h>
>> +#include <linux/crypto.h>
>> +#include <linux/mempool.h>
>> +#include <linux/zsmalloc.h>
>> +
>> +#include <linux/mm_types.h>
>> +#include <linux/page-flags.h>
>> +#include <linux/swapops.h>
>> +#include <linux/writeback.h>
>> +#include <linux/pagemap.h>
>> +
>> +/*********************************
>> +* statistics
>> +**********************************/
>> +/* Number of memory pages used by the compressed pool */
>> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
>> +/* The number of compressed pages currently stored in zswap */
>> +static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
>> +/* The number of outstanding pages awaiting writeback */
>> +static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
>> +
>> +/*
>> + * The statistics below are not protected from concurrent access for
>> + * performance reasons so they may not be a 100% accurate. However,
>> + * the do provide useful information on roughly how many times a
>> + * certain event is occurring.
>> +*/
>> +static u64 zswap_flushed_pages;
>> +static u64 zswap_reject_compress_poor;
>> +static u64 zswap_flush_attempted;
>> +static u64 zswap_reject_tmppage_fail;
>> +static u64 zswap_reject_flush_fail;
>> +static u64 zswap_reject_zsmalloc_fail;
>> +static u64 zswap_reject_kmemcache_fail;
>> +static u64 zswap_saved_by_flush;
>> +static u64 zswap_duplicate_entry;
>> +
>> +/*********************************
>> +* tunables
>> +**********************************/
>> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
>> +static bool zswap_enabled;
>> +module_param_named(enabled, zswap_enabled, bool, 0);
>
> It seems default is disable at the moment?
Yes, that's right. While zswap should be always-on safe (i.e. no
impact if swap isn't being used), I thought this would be the safe way
for now.
>
>> +
>> +/* Compressor to be used by zswap (fixed at boot for now) */
>> +#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
>> +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
>> +module_param_named(compressor, zswap_compressor, charp, 0);
>> +
>> +/* The maximum percentage of memory that the compressed pool can occupy */
>> +static unsigned int zswap_max_pool_percent = 20;
>> +module_param_named(max_pool_percent,
>> + zswap_max_pool_percent, uint, 0644);
>> +
>> +/*
>> + * Maximum compression ratio, as as percentage, for an acceptable
>> + * compressed page. Any pages that do not compress by at least
>> + * this ratio will be rejected.
>> +*/
>> +static unsigned int zswap_max_compression_ratio = 80;
>> +module_param_named(max_compression_ratio,
>> + zswap_max_compression_ratio, uint, 0644);
>> +
>> +/*
>> + * Maximum number of outstanding flushes allowed at any given time.
>> + * This is to prevent decompressing an unbounded number of compressed
>> + * pages into the swap cache all at once, and to help with writeback
>> + * congestion.
>> +*/
>> +#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
>> +
>> +/*********************************
>> +* compression functions
>> +**********************************/
>> +/* per-cpu compression transforms */
>> +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
>> +
>> +enum comp_op {
>> + ZSWAP_COMPOP_COMPRESS,
>> + ZSWAP_COMPOP_DECOMPRESS
>> +};
>> +
>> +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
>> + u8 *dst, unsigned int *dlen)
>> +{
>> + struct crypto_comp *tfm;
>> + int ret;
>> +
>> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
>> + switch (op) {
>> + case ZSWAP_COMPOP_COMPRESS:
>> + ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
>> + break;
>> + case ZSWAP_COMPOP_DECOMPRESS:
>> + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
>> + break;
>> + default:
>> + ret = -EINVAL;
>> + }
>> +
>> + put_cpu();
>> + return ret;
>> +}
>> +
>> +static int __init zswap_comp_init(void)
>> +{
>> + if (!crypto_has_comp(zswap_compressor, 0, 0)) {
>> + pr_info("zswap: %s compressor not available\n",
>> + zswap_compressor);
>> + /* fall back to default compressor */
>> + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
>> + if (!crypto_has_comp(zswap_compressor, 0, 0))
>> + /* can't even load the default compressor */
>> + return -ENODEV;
>> + }
>> + pr_info("zswap: using %s compressor\n", zswap_compressor);
>> +
>> + /* alloc percpu transforms */
>> + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
>> + if (!zswap_comp_pcpu_tfms)
>> + return -ENOMEM;
>> + return 0;
>> +}
>> +
>> +static void zswap_comp_exit(void)
>> +{
>> + /* free percpu transforms */
>> + if (zswap_comp_pcpu_tfms)
>> + free_percpu(zswap_comp_pcpu_tfms);
>> +}
>> +
>> +/*********************************
>> +* data structures
>> +**********************************/
>> +struct zswap_entry {
>> + struct rb_node rbnode;
>> + struct list_head lru;
>> + int refcount;
>> + unsigned type;
>> + pgoff_t offset;
>> + unsigned long handle;
>> + unsigned int length;
>> +};
>> +
>> +/*
>> + * The tree lock in the zswap_tree struct protects a few things:
>> + * - the rbtree
>> + * - the lru list
>> + * - the refcount field of each entry in the tree
>> + */
>> +struct zswap_tree {
>> + struct rb_root rbroot;
>> + struct list_head lru;
>> + spinlock_t lock;
>> + struct zs_pool *pool;
>> +};
>> +
>> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
>> +
>> +/*********************************
>> +* zswap entry functions
>> +**********************************/
>> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
>> +static struct kmem_cache *zswap_entry_cache;
>> +
>> +static inline int zswap_entry_cache_create(void)
>> +{
>> + zswap_entry_cache =
>> + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
>> + sizeof(struct zswap_entry), 0, 0, NULL);
>> + return (zswap_entry_cache == NULL);
>> +}
>> +
>> +static inline void zswap_entry_cache_destory(void)
>> +{
>> + kmem_cache_destroy(zswap_entry_cache);
>> +}
>> +
>> +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
>> +{
>> + struct zswap_entry *entry;
>> + entry = kmem_cache_alloc(zswap_entry_cache, gfp);
>> + if (!entry)
>> + return NULL;
>> + INIT_LIST_HEAD(&entry->lru);
>> + entry->refcount = 1;
>> + return entry;
>> +}
>> +
>> +static inline void zswap_entry_cache_free(struct zswap_entry *entry)
>> +{
>> + kmem_cache_free(zswap_entry_cache, entry);
>> +}
>> +
>> +static inline void zswap_entry_get(struct zswap_entry *entry)
>> +{
>> + entry->refcount++;
>> +}
>> +
>> +static inline int zswap_entry_put(struct zswap_entry *entry)
>> +{
>> + entry->refcount--;
>> + return entry->refcount;
>> +}
>> +
>> +/*********************************
>> +* rbtree functions
>> +**********************************/
>> +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
>> +{
>> + struct rb_node *node = root->rb_node;
>> + struct zswap_entry *entry;
>> +
>> + while (node) {
>> + entry = rb_entry(node, struct zswap_entry, rbnode);
>> + if (entry->offset > offset)
>> + node = node->rb_left;
>> + else if (entry->offset < offset)
>> + node = node->rb_right;
>> + else
>> + return entry;
>> + }
>> + return NULL;
>> +}
>> +
>> +/*
>> + * In the case that a entry with the same offset is found, it a pointer to
>> + * the existing entry is stored in dupentry and the function returns -EEXIST
>> +*/
>> +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
>> + struct zswap_entry **dupentry)
>> +{
>> + struct rb_node **link = &root->rb_node, *parent = NULL;
>> + struct zswap_entry *myentry;
>> +
>> + while (*link) {
>> + parent = *link;
>> + myentry = rb_entry(parent, struct zswap_entry, rbnode);
>> + if (myentry->offset > entry->offset)
>> + link = &(*link)->rb_left;
>> + else if (myentry->offset < entry->offset)
>> + link = &(*link)->rb_right;
>> + else {
>> + *dupentry = myentry;
>> + return -EEXIST;
>> + }
>> + }
>> + rb_link_node(&entry->rbnode, parent, link);
>> + rb_insert_color(&entry->rbnode, root);
>> + return 0;
>> +}
>> +
>> +/*********************************
>> +* per-cpu code
>> +**********************************/
>> +static DEFINE_PER_CPU(u8 *, zswap_dstmem);
>> +
>> +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
>> +{
>> + struct crypto_comp *tfm;
>> + u8 *dst;
>> +
>> + switch (action) {
>> + case CPU_UP_PREPARE:
>> + tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
>> + if (IS_ERR(tfm)) {
>> + pr_err("zswap: can't allocate compressor transform\n");
>> + return NOTIFY_BAD;
>> + }
>> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
>> + dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
>> + if (!dst) {
>> + pr_err("zswap: can't allocate compressor buffer\n");
>> + crypto_free_comp(tfm);
>> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
>> + return NOTIFY_BAD;
>> + }
>> + per_cpu(zswap_dstmem, cpu) = dst;
>> + break;
>> + case CPU_DEAD:
>> + case CPU_UP_CANCELED:
>> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
>> + if (tfm) {
>> + crypto_free_comp(tfm);
>> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
>> + }
>> + dst = per_cpu(zswap_dstmem, cpu);
>> + if (dst) {
>> + free_pages((unsigned long)dst, 1);
>> + per_cpu(zswap_dstmem, cpu) = NULL;
>> + }
>> + break;
>> + default:
>> + break;
>> + }
>> + return NOTIFY_OK;
>> +}
>> +
>> +static int zswap_cpu_notifier(struct notifier_block *nb,
>> + unsigned long action, void *pcpu)
>> +{
>> + unsigned long cpu = (unsigned long)pcpu;
>> + return __zswap_cpu_notifier(action, cpu);
>> +}
>> +
>> +static struct notifier_block zswap_cpu_notifier_block = {
>> + .notifier_call = zswap_cpu_notifier
>> +};
>> +
>> +static int zswap_cpu_init(void)
>> +{
>> + unsigned long cpu;
>> +
>> + get_online_cpus();
>> + for_each_online_cpu(cpu)
>> + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
>> + goto cleanup;
>> + register_cpu_notifier(&zswap_cpu_notifier_block);
>> + put_online_cpus();
>> + return 0;
>> +
>> +cleanup:
>> + for_each_online_cpu(cpu)
>> + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
>> + put_online_cpus();
>> + return -ENOMEM;
>> +}
>> +
>> +/*********************************
>> +* zsmalloc callbacks
>> +**********************************/
>> +static mempool_t *zswap_page_pool;
>> +
>> +static u64 zswap_pool_limit_hit;
>> +
>> +static inline unsigned int zswap_max_pool_pages(void)
>> +{
>> + return zswap_max_pool_percent * totalram_pages / 100;
>> +}
>> +
>> +static inline int zswap_page_pool_create(void)
>> +{
>> + zswap_page_pool = mempool_create_page_pool(256, 0);
>
> Could you write down why you select pool to 256?
> If you have a plan, please write down it as TODO.
> I think it could be a function of zswap_max_pool_pages with min/max.
Yes, that would probably be better.
>
> Another question.
>
> What's the benefit of using mempool for zsmalloc?
> As you know, zsmalloc doesn't use mempool as default.
> I guess you see some benefit. if so, zram could be changed.
> If we can change zsmalloc's default scheme to use mempool,
> all of customer of zsmalloc could be enhanced, too.
In the case of zswap, through experimentation, I found that adding a
mempool behind the zsmalloc pool added some elasticity to the pool.
Fewer stores failed if we kept a small reserve of pages around instead
of having to go back to the buddy allocator who, under memory
pressure, is more likely to reject our request.
I don't see this situation being applicable to all zsmalloc users
however. I don't think we want incorporate it directly into zsmalloc
for now. The ability to register custom page alloc/free functions at
pool creation time allows users to do something special, like back
with a mempool, if they want to do that.
>
>> + if (!zswap_page_pool)
>> + return -ENOMEM;
>> + return 0;
>> +}
>> +
>> +static inline void zswap_page_pool_destroy(void)
>> +{
>> + mempool_destroy(zswap_page_pool);
>> +}
>> +
>> +static struct page *zswap_alloc_page(gfp_t flags)
>> +{
>> + struct page *page;
>> +
>> + if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
>> + zswap_pool_limit_hit++;
>> + return NULL;
>> + }
>> + page = mempool_alloc(zswap_page_pool, flags);
>> + if (page)
>> + atomic_inc(&zswap_pool_pages);
>> + return page;
>> +}
>> +
>> +static void zswap_free_page(struct page *page)
>> +{
>> + mempool_free(page, zswap_page_pool);
>> + atomic_dec(&zswap_pool_pages);
>
> Nit.
>
> By semantic, free function can receive NULL argument so
> atomic_dec would be nice to check it before decreasing count.
Are you saying I should check the page != NULL before doing anything
here? If so, I can add that.
>
>> +}
>> +
>> +static struct zs_ops zswap_zs_ops = {
>> + .alloc = zswap_alloc_page,
>> + .free = zswap_free_page
>> +};
>> +
>> +/*********************************
>> +* flush code
>> +**********************************/
>> +static void zswap_end_swap_write(struct bio *bio, int err)
>> +{
>> + end_swap_bio_write(bio, err);
>> + atomic_dec(&zswap_outstanding_flushes);
>> + zswap_flushed_pages++;
>> +}
>> +
>> +/*
>> + * zswap_get_swap_cache_page
>> + *
>> + * This is an adaption of read_swap_cache_async()
>> + *
>> + * If success, page is returned in retpage
>> + * Returns 0 if page was already in the swap cache, page is not locked
>> + * Returns 1 if the new page needs to be populated, page is locked
>> + */
>> +static int zswap_get_swap_cache_page(swp_entry_t entry,
>> + struct page **retpage)
>> +{
>> + struct page *found_page, *new_page = NULL;
>> + int err;
>> +
>> + *retpage = NULL;
>> + do {
>> + /*
>> + * First check the swap cache. Since this is normally
>> + * called after lookup_swap_cache() failed, re-calling
>> + * that would confuse statistics.
>> + */
>> + found_page = find_get_page(&swapper_space, entry.val);
>> + if (found_page)
>> + break;
>> +
>> + /*
>> + * Get a new page to read into from swap.
>> + */
>> + if (!new_page) {
>> + new_page = alloc_page(GFP_KERNEL);
>> + if (!new_page)
>> + break; /* Out of memory */
>> + }
>> +
>> + /*
>> + * call radix_tree_preload() while we can wait.
>> + */
>> + err = radix_tree_preload(GFP_KERNEL);
>> + if (err)
>> + break;
>> +
>> + /*
>> + * Swap entry may have been freed since our caller observed it.
>> + */
>> + err = swapcache_prepare(entry);
>> + if (err == -EEXIST) { /* seems racy */
>> + radix_tree_preload_end();
>> + continue;
>> + }
>> + if (err) { /* swp entry is obsolete ? */
>> + radix_tree_preload_end();
>> + break;
>> + }
>> +
>> + /* May fail (-ENOMEM) if radix-tree node allocation failed. */
>> + __set_page_locked(new_page);
>> + SetPageSwapBacked(new_page);
>> + err = __add_to_swap_cache(new_page, entry);
>> + if (likely(!err)) {
>> + radix_tree_preload_end();
>> + lru_cache_add_anon(new_page);
>> + *retpage = new_page;
>> + return 1;
>> + }
>> + radix_tree_preload_end();
>> + ClearPageSwapBacked(new_page);
>> + __clear_page_locked(new_page);
>> + /*
>> + * add_to_swap_cache() doesn't return -EEXIST, so we can safely
>> + * clear SWAP_HAS_CACHE flag.
>> + */
>> + swapcache_free(entry, NULL);
>> + } while (err != -ENOMEM);
>> +
>> + if (new_page)
>> + page_cache_release(new_page);
>> + if (!found_page)
>> + return -ENOMEM;
>> + *retpage = found_page;
>> + return 0;
>> +}
>> +
>> +static int zswap_flush_entry(struct zswap_entry *entry)
>> +{
>> + unsigned long type = entry->type;
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct page *page;
>> + swp_entry_t swpentry;
>> + u8 *src, *dst;
>> + unsigned int dlen;
>> + int ret, refcount;
>> + struct writeback_control wbc = {
>> + .sync_mode = WB_SYNC_NONE,
>> + };
>> +
>> + /* get/allocate page in the swap cache */
>> + swpentry = swp_entry(type, entry->offset);
>> + ret = zswap_get_swap_cache_page(swpentry, &page);
>> + if (ret < 0)
>> + return ret;
>> + else if (ret) {
>> + /* decompress */
>> + dlen = PAGE_SIZE;
>> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
>> + dst = kmap_atomic(page);
>> + ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
>> + dst, &dlen);
>> + kunmap_atomic(dst);
>> + zs_unmap_object(tree->pool, entry->handle);
>> + BUG_ON(ret);
>> + BUG_ON(dlen != PAGE_SIZE);
>> + SetPageUptodate(page);
>> + } else {
>> + /* page is already in the swap cache, ignore for now */
>> + spin_lock(&tree->lock);
>> + refcount = zswap_entry_put(entry);
>> + spin_unlock(&tree->lock);
>> +
>> + if (likely(refcount))
>> + return 0;
>> +
>> + /* if the refcount is zero, invalidate must have come in */
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +
>> + return 0;
>> + }
>> +
>> + /* start writeback */
>> + SetPageReclaim(page);
>> + /*
>> + * Return value is ignored here because it doesn't change anything
>> + * for us. Page is returned unlocked.
>> + */
>> + (void)__swap_writepage(page, &wbc, zswap_end_swap_write);
>> + page_cache_release(page);
>> + atomic_inc(&zswap_outstanding_flushes);
>> +
>> + /* remove */
>> + spin_lock(&tree->lock);
>> + refcount = zswap_entry_put(entry);
>> + if (refcount > 1) {
>> + /* load in progress, load will free */
>> + spin_unlock(&tree->lock);
>> + return 0;
>> + }
>> + if (refcount == 1)
>> + /* no invalidate yet, remove from rbtree */
>> + rb_erase(&entry->rbnode, &tree->rbroot);
>> + spin_unlock(&tree->lock);
>> +
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +
>> + return 0;
>> +}
>> +
>> +static void zswap_flush_entries(unsigned type, int nr)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry;
>> + int i, ret;
>> +
>> +/*
>> + * This limits is arbitrary for now until a better
>> + * policy can be implemented. This is so we don't
>> + * eat all of RAM decompressing pages for writeback.
>> + */
>> + if (atomic_read(&zswap_outstanding_flushes) >
>> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
>> + return;
>> +
>> + for (i = 0; i < nr; i++) {
>> + /* dequeue from lru */
>> + spin_lock(&tree->lock);
>> + if (list_empty(&tree->lru)) {
>> + spin_unlock(&tree->lock);
>> + break;
>> + }
>> + entry = list_first_entry(&tree->lru,
>> + struct zswap_entry, lru);
>> + list_del(&entry->lru);
>> + zswap_entry_get(entry);
>> + spin_unlock(&tree->lock);
>> + ret = zswap_flush_entry(entry);
>> + if (ret) {
>> + /* put back on the lru */
>> + spin_lock(&tree->lock);
>> + list_add(&entry->lru, &tree->lru);
>> + spin_unlock(&tree->lock);
>> + } else {
>> + if (atomic_read(&zswap_outstanding_flushes) >
>> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
>> + break;
>> + }
>> + }
>> +}
>
> The flush part complexity is very high so we needs careful review.
> I hope you can make the patch step by step from ugly approach to smart one.
> It helps reviewers much.
> If it isn't easy, I will review as it is.
(see comment at top)
>
>> +
>> +/*******************************************
>> +* page pool for temporary compression result
>> +********************************************/
>> +#define ZSWAP_TMPPAGE_POOL_PAGES 16
>> +static LIST_HEAD(zswap_tmppage_list);
>> +static DEFINE_SPINLOCK(zswap_tmppage_lock);
>> +
>> +static void zswap_tmppage_pool_destroy(void)
>> +{
>> + struct page *page, *tmppage;
>> +
>> + spin_lock(&zswap_tmppage_lock);
>> + list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
>> + list_del(&page->lru);
>> + __free_pages(page, 1);
>> + }
>> + spin_unlock(&zswap_tmppage_lock);
>> +}
>> +
>> +static int zswap_tmppage_pool_create(void)
>> +{
>> + int i;
>> + struct page *page;
>> +
>> + for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
>> + page = alloc_pages(GFP_KERNEL, 1);
>> + if (!page) {
>> + zswap_tmppage_pool_destroy();
>> + return -ENOMEM;
>> + }
>> + spin_lock(&zswap_tmppage_lock);
>> + list_add(&page->lru, &zswap_tmppage_list);
>> + spin_unlock(&zswap_tmppage_lock);
>> + }
>> + return 0;
>> +}
>> +
>> +static inline struct page *zswap_tmppage_alloc(void)
>> +{
>> + struct page *page;
>> +
>> + spin_lock(&zswap_tmppage_lock);
>> + if (list_empty(&zswap_tmppage_list)) {
>> + spin_unlock(&zswap_tmppage_lock);
>> + return NULL;
>> + }
>> + page = list_first_entry(&zswap_tmppage_list, struct page, lru);
>> + list_del(&page->lru);
>> + spin_unlock(&zswap_tmppage_lock);
>> + return page;
>> +}
>> +
>> +static inline void zswap_tmppage_free(struct page *page)
>> +{
>> + spin_lock(&zswap_tmppage_lock);
>> + list_add(&page->lru, &zswap_tmppage_list);
>> + spin_unlock(&zswap_tmppage_lock);
>> +}
>> +
>> +/*********************************
>> +* frontswap hooks
>> +**********************************/
>> +/* attempts to compress and store an single page */
>> +static int zswap_frontswap_store(unsigned type, pgoff_t offset, struct page *page)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry, *dupentry;
>> + int ret;
>> + unsigned int dlen = PAGE_SIZE;
>> + unsigned long handle;
>> + char *buf;
>> + u8 *src, *dst, *tmpdst;
>> + struct page *tmppage;
>> + bool flush_attempted = 0;
>> +
>> + if (!tree) {
>> + ret = -ENODEV;
>> + goto reject;
>> + }
>> +
>> + /* compress */
>> + dst = get_cpu_var(zswap_dstmem);
>> + src = kmap_atomic(page);
>> + ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
>> + kunmap_atomic(src);
>> + if (ret) {
>> + ret = -EINVAL;
>> + goto freepage;
>> + }
>> + if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
>> + zswap_reject_compress_poor++;
>> + ret = -E2BIG;
>> + goto freepage;
>> + }
>> +
>> + /* store */
>> + handle = zs_malloc(tree->pool, dlen,
>> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
>> + __GFP_NOWARN);
>> + if (!handle) {
>> + zswap_flush_attempted++;
>> + /*
>> + * Copy compressed buffer out of per-cpu storage so
>> + * we can re-enable preemption.
>> + */
>> + tmppage = zswap_tmppage_alloc();
>> + if (!tmppage) {
>> + zswap_reject_tmppage_fail++;
>> + ret = -ENOMEM;
>> + goto freepage;
>> + }
>> + flush_attempted = 1;
>> + tmpdst = page_address(tmppage);
>> + memcpy(tmpdst, dst, dlen);
>> + dst = tmpdst;
>> + put_cpu_var(zswap_dstmem);
>> +
>> + /* try to free up some space */
>> + /* TODO: replace with more targeted policy */
>> + zswap_flush_entries(type, 16);
>> + /* try again, allowing wait */
>> + handle = zs_malloc(tree->pool, dlen,
>> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
>> + __GFP_NOWARN);
>> + if (!handle) {
>> + /* still no space, fail */
>> + zswap_reject_zsmalloc_fail++;
>> + ret = -ENOMEM;
>> + goto freepage;
>> + }
>> + zswap_saved_by_flush++;
>> + }
>> +
>> + buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
>> + memcpy(buf, dst, dlen);
>> + zs_unmap_object(tree->pool, handle);
>> + if (flush_attempted)
>> + zswap_tmppage_free(tmppage);
>> + else
>> + put_cpu_var(zswap_dstmem);
>> +
>> + /* allocate entry */
>> + entry = zswap_entry_cache_alloc(GFP_KERNEL);
>> + if (!entry) {
>
> zs_free
Good catch!
>
>> + zswap_reject_kmemcache_fail++;
>> + ret = -ENOMEM;
>> + goto reject;
>> + }
>> +
>> + /* populate entry */
>> + entry->type = type;
>> + entry->offset = offset;
>> + entry->handle = handle;
>> + entry->length = dlen;
>> +
>> + /* map */
>> + spin_lock(&tree->lock);
>> + do {
>> + ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
>
> Could you describe why existing entry could be there?
> IIUC, it is caused by delayed swap slot free of VM. Right?
Honestly, I don't know. A comment in the frontswap code said I need
to handle this case, but I'm not sure under what conditions it
happens. I know that it very rarely _does_ happen because I had a bug
during development related to this path.
I'll see if I can get an answer for you.
> Anyway, it would be nice to add comment about it.
>
>
>> + if (ret == -EEXIST) {
>> + zswap_duplicate_entry++;
>> + /* remove from rbtree and lru */
>> + rb_erase(&dupentry->rbnode, &tree->rbroot);
>> + if (dupentry->lru.next != LIST_POISON1)
>
> Why do we need this check? Is there any case entry isn't linked at LRU list?
> Because you already removed it in load part. Right?
Yes, it could be in the process of being loaded or flushed, either one
will have detached the entry from the list.
> Let's add comment about that.
Will do.
> And let's not dependent on LIST_POISON1 of
> list util but use explicit zswap's one.
Good suggestion.
>
>> + list_del(&dupentry->lru);
>> + if (!zswap_entry_put(dupentry)) {
>> + /* free */
>> + zs_free(tree->pool, dupentry->handle);
>> + zswap_entry_cache_free(dupentry);
>> + atomic_dec(&zswap_stored_pages);
>> + }
>> + }
>> + } while (ret == -EEXIST);
>> + list_add_tail(&entry->lru, &tree->lru);
>> + spin_unlock(&tree->lock);
>> +
>> + /* update stats */
>> + atomic_inc(&zswap_stored_pages);
>> +
>> + return 0;
>> +
>> +freepage:
>> + if (flush_attempted)
>> + zswap_tmppage_free(tmppage);
>> + else
>> + put_cpu_var(zswap_dstmem);
>> +reject:
>> + return ret;
>> +}
>> +
>> +/*
>> + * returns 0 if the page was successfully decompressed
>> + * return -1 on entry not found or error
>> +*/
>> +static int zswap_frontswap_load(unsigned type, pgoff_t offset, struct page *page)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry;
>> + u8 *src, *dst;
>> + unsigned int dlen;
>> + int refcount;
>> +
>> + /* find */
>> + spin_lock(&tree->lock);
>> + entry = zswap_rb_search(&tree->rbroot, offset);
>> + if (!entry) {
>> + /* entry was flushed */
>> + spin_unlock(&tree->lock);
>> + return -1;
>> + }
>> + zswap_entry_get(entry);
>> +
>> + /* remove from lru */
>> + if (entry->lru.next != LIST_POISON1)
>
> When do we encounter this case?
> By racing with flush?
Yes.
> Need comment, too.
Yes.
>
>> + list_del(&entry->lru);
>> + spin_unlock(&tree->lock);
>> +
>> + /* decompress */
>> + dlen = PAGE_SIZE;
>> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
>> + dst = kmap_atomic(page);
>> + zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
>> + dst, &dlen);
>> + kunmap_atomic(dst);
>> + zs_unmap_object(tree->pool, entry->handle);
>> +
>> + spin_lock(&tree->lock);
>> + refcount = zswap_entry_put(entry);
>> + if (likely(refcount)) {
>> + list_add_tail(&entry->lru, &tree->lru);
>> + spin_unlock(&tree->lock);
>> + return 0;
>> + }
>> + spin_unlock(&tree->lock);
>> +
>> + /*
>> + * We don't have to unlink from the rbtree because zswap_flush_entry()
>> + * or zswap_frontswap_invalidate page() has already done this for us if we
>> + * are the last reference.
>> + */
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +
>> + return 0;
>> +}
>> +
>> +/* invalidates a single page */
>> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry;
>> + int refcount;
>> +
>> + if (!tree)
>
> When do we encounter this case?
Upon second look, I'm not sure that we do. The check in
zswap_frontswap_store() prevents pages from being stored for a
particular swap type if the tree allocation for that type failed
during zswap_frontswap_init().
In that case checking the frontswap_map should prevent any call to
load or invalidate that entry.
I'll make sure. If that is the case, I'll remove this check.
Thanks again for the review!
Seth
>
>> + return;
>> +
>> + /* find */
>> + spin_lock(&tree->lock);
>> + entry = zswap_rb_search(&tree->rbroot, offset);
>> + if (!entry) {
>> + /* entry was flushed */
>> + spin_unlock(&tree->lock);
>> + return;
>> + }
>> +
>> + /* remove from rbtree and lru */
>> + rb_erase(&entry->rbnode, &tree->rbroot);
>> + if (entry->lru.next != LIST_POISON1)
>> + list_del(&entry->lru);
>> + refcount = zswap_entry_put(entry);
>> + spin_unlock(&tree->lock);
>> + if (refcount) {
>> + /* must be flushing */
>> + return;
>> + }
>> +
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +}
>> +
>> +/* invalidates all pages for the given swap type */
>> +static void zswap_frontswap_invalidate_area(unsigned type)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct rb_node *node, *next;
>> + struct zswap_entry *entry;
>> +
>> + if (!tree)
>
> When do we encounter this case?
We can encouter this case.
Since the zswap_frontswap_init() has a void return type, the upper
layer can't know that we failed the tree allocation during swapon.
During a swapoff, it will call zswap_frontswap_invalidate_area(). So
checking !tree is the way we determine if zswap_frontswap_init()
failed at swapon time. If so, there is nothing to do.
>
>> + return;
>> +
>> + /* walk the tree and free everything */
>> + spin_lock(&tree->lock);
>> + node = rb_first(&tree->rbroot);
>> + while (node) {
>> + entry = rb_entry(node, struct zswap_entry, rbnode);
>> + zs_free(tree->pool, entry->handle);
>> + next = rb_next(node);
>> + zswap_entry_cache_free(entry);
>> + node = next;
>> + }
>> + tree->rbroot = RB_ROOT;
>> + INIT_LIST_HEAD(&tree->lru);
>> + spin_unlock(&tree->lock);
>> +}
>> +
>> +/* NOTE: this is called in atomic context from swapon and must not sleep */
>> +static void zswap_frontswap_init(unsigned type)
>> +{
>> + struct zswap_tree *tree;
>> +
>> + tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
>> + if (!tree)
>> + goto err;
>> + tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
>> + if (!tree->pool)
>> + goto freetree;
>> + tree->rbroot = RB_ROOT;
>> + INIT_LIST_HEAD(&tree->lru);
>> + spin_lock_init(&tree->lock);
>> + zswap_trees[type] = tree;
>> + return;
>> +
>> +freetree:
>> + kfree(tree);
>> +err:
>> + pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
>> +}
>> +
>> +static struct frontswap_ops zswap_frontswap_ops = {
>> + .store = zswap_frontswap_store,
>> + .load = zswap_frontswap_load,
>> + .invalidate_page = zswap_frontswap_invalidate_page,
>> + .invalidate_area = zswap_frontswap_invalidate_area,
>> + .init = zswap_frontswap_init
>> +};
>> +
>> +/*********************************
>> +* debugfs functions
>> +**********************************/
>> +#ifdef CONFIG_DEBUG_FS
>> +#include <linux/debugfs.h>
>> +
>> +static struct dentry *zswap_debugfs_root;
>> +
>> +static int __init zswap_debugfs_init(void)
>> +{
>> + if (!debugfs_initialized())
>> + return -ENODEV;
>> +
>> + zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
>> + if (!zswap_debugfs_root)
>> + return -ENOMEM;
>> +
>> + debugfs_create_u64("saved_by_flush", S_IRUGO,
>> + zswap_debugfs_root, &zswap_saved_by_flush);
>> + debugfs_create_u64("pool_limit_hit", S_IRUGO,
>> + zswap_debugfs_root, &zswap_pool_limit_hit);
>> + debugfs_create_u64("reject_flush_attempted", S_IRUGO,
>> + zswap_debugfs_root, &zswap_flush_attempted);
>> + debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_tmppage_fail);
>> + debugfs_create_u64("reject_flush_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_flush_fail);
>> + debugfs_create_u64("reject_zsmalloc_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_zsmalloc_fail);
>> + debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_kmemcache_fail);
>> + debugfs_create_u64("reject_compress_poor", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_compress_poor);
>> + debugfs_create_u64("flushed_pages", S_IRUGO,
>> + zswap_debugfs_root, &zswap_flushed_pages);
>> + debugfs_create_u64("duplicate_entry", S_IRUGO,
>> + zswap_debugfs_root, &zswap_duplicate_entry);
>> + debugfs_create_atomic_t("pool_pages", S_IRUGO,
>> + zswap_debugfs_root, &zswap_pool_pages);
>> + debugfs_create_atomic_t("stored_pages", S_IRUGO,
>> + zswap_debugfs_root, &zswap_stored_pages);
>> + debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
>> + zswap_debugfs_root, &zswap_outstanding_flushes);
>> +
>> + return 0;
>> +}
>> +
>> +static void __exit zswap_debugfs_exit(void)
>> +{
>> + if (zswap_debugfs_root)
>> + debugfs_remove_recursive(zswap_debugfs_root);
>> +}
>> +#else
>> +static inline int __init zswap_debugfs_init(void)
>> +{
>> + return 0;
>> +}
>> +
>> +static inline void __exit zswap_debugfs_exit(void) { }
>> +#endif
>> +
>> +/*********************************
>> +* module init and exit
>> +**********************************/
>> +static int __init init_zswap(void)
>> +{
>> + if (!zswap_enabled)
>> + return 0;
>> +
>> + pr_info("loading zswap\n");
>> + if (zswap_entry_cache_create()) {
>> + pr_err("zswap: entry cache creation failed\n");
>> + goto error;
>> + }
>> + if (zswap_page_pool_create()) {
>> + pr_err("zswap: page pool initialization failed\n");
>> + goto pagepoolfail;
>> + }
>> + if (zswap_tmppage_pool_create()) {
>> + pr_err("zswap: workmem pool initialization failed\n");
>> + goto tmppoolfail;
>> + }
>> + if (zswap_comp_init()) {
>> + pr_err("zswap: compressor initialization failed\n");
>> + goto compfail;
>> + }
>> + if (zswap_cpu_init()) {
>> + pr_err("zswap: per-cpu initialization failed\n");
>> + goto pcpufail;
>> + }
>> + frontswap_register_ops(&zswap_frontswap_ops);
>> + if (zswap_debugfs_init())
>> + pr_warn("zswap: debugfs initialization failed\n");
>> + return 0;
>> +pcpufail:
>> + zswap_comp_exit();
>> +compfail:
>> + zswap_tmppage_pool_destroy();
>> +tmppoolfail:
>> + zswap_page_pool_destroy();
>> +pagepoolfail:
>> + zswap_entry_cache_destory();
>> +error:
>> + return -ENOMEM;
>> +}
>> +/* must be late so crypto has time to come up */
>> +late_initcall(init_zswap);
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
>> +MODULE_DESCRIPTION("Compression backend for frontswap pages");
>> --
>> 1.7.9.5
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org. For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
@ 2013-01-29 17:26 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-29 17:26 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On 01/29/2013 12:27 AM, Minchan Kim wrote:
> First feeling is it's simple and nice approach.
> Although we have some problems to decide policy, it could solve by later patch
> so I hope we make basic infrasture more solid by lots of comment.
Thanks very much for the review!
>
> There are two things to review hard.
>
> 1. data structure life - when any data structure is died by whom?
> Please write down it in changelog or header of zswap.c
>
> 2. Flush routine - I hope it would be nice to separate it as another
> incremental patches if it is possible. If it's impossible, let's add
> lots of words.
It seems like it would be difficult to break the flushing
functionality into it's own patch, but I can start the process and
see. As long as people keep in mind that some of the design rationale
in the version without the flush code is dictated by the addition of
the flush code.
But yes, more comments.
> On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
>> zswap is a thin compression backend for frontswap. It receives
>> pages from frontswap and attempts to store them in a compressed
>> memory pool, resulting in an effective partial memory reclaim and
>> dramatically reduced swap device I/O.
>>
>> Additional, in most cases, pages can be retrieved from this
>> compressed store much more quickly than reading from tradition
>> swap devices resulting in faster performance for many workloads.
>>
>> This patch adds the zswap driver to mm/
>>
>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>> ---
>> mm/Kconfig | 15 +
>> mm/Makefile | 1 +
>> mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 1089 insertions(+)
>> create mode 100644 mm/zswap.c
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 278e3ab..14b9acb 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -446,3 +446,18 @@ config FRONTSWAP
>> and swap data is stored as normal on the matching swap device.
>>
>> If unsure, say Y to enable frontswap.
>> +
>> +config ZSWAP
>> + bool "In-kernel swap page compression"
>> + depends on FRONTSWAP && CRYPTO
>
> Couldn't we support CRYPTO optionally?
No. zswap depends on the cryptographic API for access to the
compression modules.
>
>> + select CRYPTO_LZO
>> + select ZSMALLOC
>> + default n
>> + help
>> + Zswap is a backend for the frontswap mechanism in the VMM.
>> + It receives pages from frontswap and attempts to store them
>> + in a compressed memory pool, resulting in an effective
>> + partial memory reclaim. In addition, pages and be retrieved
>> + from this compressed store much faster than most tradition
>> + swap devices resulting in reduced I/O and faster performance
>> + for many workloads.
>> diff --git a/mm/Makefile b/mm/Makefile
>> index 3a46287..1b1ed5c 100644
>> --- a/mm/Makefile
>> +++ b/mm/Makefile
>> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
>> obj-$(CONFIG_BOUNCE) += bounce.o
>> obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
>> obj-$(CONFIG_FRONTSWAP) += frontswap.o
>> +obj-$(CONFIG_ZSWAP) += zswap.o
>> obj-$(CONFIG_HAS_DMA) += dmapool.o
>> obj-$(CONFIG_HUGETLBFS) += hugetlb.o
>> obj-$(CONFIG_NUMA) += mempolicy.o
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> new file mode 100644
>> index 0000000..050b6db
>> --- /dev/null
>> +++ b/mm/zswap.c
>> @@ -0,0 +1,1073 @@
>> +/*
>> + * zswap-drv.c - zswap driver file
>> + *
>> + * zswap is a backend for frontswap that takes pages that are in the
>> + * process of being swapped out and attempts to compress them and store
>> + * them in a RAM-based memory pool. This results in a significant I/O
>> + * reduction on the real swap device and, in the case of a slow swap
>> + * device, can also improve workload performance.
>> + *
>> + * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
>> + *
>> + * This program is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU General Public License
>> + * as published by the Free Software Foundation; either version 2
>> + * of the License, or (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> + * GNU General Public License for more details.
>> +*/
>> +
>> +#include <linux/module.h>
>> +#include <linux/cpu.h>
>> +#include <linux/highmem.h>
>> +#include <linux/slab.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/types.h>
>> +#include <linux/atomic.h>
>> +#include <linux/frontswap.h>
>> +#include <linux/rbtree.h>
>> +#include <linux/swap.h>
>> +#include <linux/crypto.h>
>> +#include <linux/mempool.h>
>> +#include <linux/zsmalloc.h>
>> +
>> +#include <linux/mm_types.h>
>> +#include <linux/page-flags.h>
>> +#include <linux/swapops.h>
>> +#include <linux/writeback.h>
>> +#include <linux/pagemap.h>
>> +
>> +/*********************************
>> +* statistics
>> +**********************************/
>> +/* Number of memory pages used by the compressed pool */
>> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
>> +/* The number of compressed pages currently stored in zswap */
>> +static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
>> +/* The number of outstanding pages awaiting writeback */
>> +static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
>> +
>> +/*
>> + * The statistics below are not protected from concurrent access for
>> + * performance reasons so they may not be a 100% accurate. However,
>> + * the do provide useful information on roughly how many times a
>> + * certain event is occurring.
>> +*/
>> +static u64 zswap_flushed_pages;
>> +static u64 zswap_reject_compress_poor;
>> +static u64 zswap_flush_attempted;
>> +static u64 zswap_reject_tmppage_fail;
>> +static u64 zswap_reject_flush_fail;
>> +static u64 zswap_reject_zsmalloc_fail;
>> +static u64 zswap_reject_kmemcache_fail;
>> +static u64 zswap_saved_by_flush;
>> +static u64 zswap_duplicate_entry;
>> +
>> +/*********************************
>> +* tunables
>> +**********************************/
>> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
>> +static bool zswap_enabled;
>> +module_param_named(enabled, zswap_enabled, bool, 0);
>
> It seems default is disable at the moment?
Yes, that's right. While zswap should be always-on safe (i.e. no
impact if swap isn't being used), I thought this would be the safe way
for now.
>
>> +
>> +/* Compressor to be used by zswap (fixed at boot for now) */
>> +#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
>> +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
>> +module_param_named(compressor, zswap_compressor, charp, 0);
>> +
>> +/* The maximum percentage of memory that the compressed pool can occupy */
>> +static unsigned int zswap_max_pool_percent = 20;
>> +module_param_named(max_pool_percent,
>> + zswap_max_pool_percent, uint, 0644);
>> +
>> +/*
>> + * Maximum compression ratio, as as percentage, for an acceptable
>> + * compressed page. Any pages that do not compress by at least
>> + * this ratio will be rejected.
>> +*/
>> +static unsigned int zswap_max_compression_ratio = 80;
>> +module_param_named(max_compression_ratio,
>> + zswap_max_compression_ratio, uint, 0644);
>> +
>> +/*
>> + * Maximum number of outstanding flushes allowed at any given time.
>> + * This is to prevent decompressing an unbounded number of compressed
>> + * pages into the swap cache all at once, and to help with writeback
>> + * congestion.
>> +*/
>> +#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
>> +
>> +/*********************************
>> +* compression functions
>> +**********************************/
>> +/* per-cpu compression transforms */
>> +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
>> +
>> +enum comp_op {
>> + ZSWAP_COMPOP_COMPRESS,
>> + ZSWAP_COMPOP_DECOMPRESS
>> +};
>> +
>> +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
>> + u8 *dst, unsigned int *dlen)
>> +{
>> + struct crypto_comp *tfm;
>> + int ret;
>> +
>> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
>> + switch (op) {
>> + case ZSWAP_COMPOP_COMPRESS:
>> + ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
>> + break;
>> + case ZSWAP_COMPOP_DECOMPRESS:
>> + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
>> + break;
>> + default:
>> + ret = -EINVAL;
>> + }
>> +
>> + put_cpu();
>> + return ret;
>> +}
>> +
>> +static int __init zswap_comp_init(void)
>> +{
>> + if (!crypto_has_comp(zswap_compressor, 0, 0)) {
>> + pr_info("zswap: %s compressor not available\n",
>> + zswap_compressor);
>> + /* fall back to default compressor */
>> + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
>> + if (!crypto_has_comp(zswap_compressor, 0, 0))
>> + /* can't even load the default compressor */
>> + return -ENODEV;
>> + }
>> + pr_info("zswap: using %s compressor\n", zswap_compressor);
>> +
>> + /* alloc percpu transforms */
>> + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
>> + if (!zswap_comp_pcpu_tfms)
>> + return -ENOMEM;
>> + return 0;
>> +}
>> +
>> +static void zswap_comp_exit(void)
>> +{
>> + /* free percpu transforms */
>> + if (zswap_comp_pcpu_tfms)
>> + free_percpu(zswap_comp_pcpu_tfms);
>> +}
>> +
>> +/*********************************
>> +* data structures
>> +**********************************/
>> +struct zswap_entry {
>> + struct rb_node rbnode;
>> + struct list_head lru;
>> + int refcount;
>> + unsigned type;
>> + pgoff_t offset;
>> + unsigned long handle;
>> + unsigned int length;
>> +};
>> +
>> +/*
>> + * The tree lock in the zswap_tree struct protects a few things:
>> + * - the rbtree
>> + * - the lru list
>> + * - the refcount field of each entry in the tree
>> + */
>> +struct zswap_tree {
>> + struct rb_root rbroot;
>> + struct list_head lru;
>> + spinlock_t lock;
>> + struct zs_pool *pool;
>> +};
>> +
>> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
>> +
>> +/*********************************
>> +* zswap entry functions
>> +**********************************/
>> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
>> +static struct kmem_cache *zswap_entry_cache;
>> +
>> +static inline int zswap_entry_cache_create(void)
>> +{
>> + zswap_entry_cache =
>> + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
>> + sizeof(struct zswap_entry), 0, 0, NULL);
>> + return (zswap_entry_cache == NULL);
>> +}
>> +
>> +static inline void zswap_entry_cache_destory(void)
>> +{
>> + kmem_cache_destroy(zswap_entry_cache);
>> +}
>> +
>> +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
>> +{
>> + struct zswap_entry *entry;
>> + entry = kmem_cache_alloc(zswap_entry_cache, gfp);
>> + if (!entry)
>> + return NULL;
>> + INIT_LIST_HEAD(&entry->lru);
>> + entry->refcount = 1;
>> + return entry;
>> +}
>> +
>> +static inline void zswap_entry_cache_free(struct zswap_entry *entry)
>> +{
>> + kmem_cache_free(zswap_entry_cache, entry);
>> +}
>> +
>> +static inline void zswap_entry_get(struct zswap_entry *entry)
>> +{
>> + entry->refcount++;
>> +}
>> +
>> +static inline int zswap_entry_put(struct zswap_entry *entry)
>> +{
>> + entry->refcount--;
>> + return entry->refcount;
>> +}
>> +
>> +/*********************************
>> +* rbtree functions
>> +**********************************/
>> +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
>> +{
>> + struct rb_node *node = root->rb_node;
>> + struct zswap_entry *entry;
>> +
>> + while (node) {
>> + entry = rb_entry(node, struct zswap_entry, rbnode);
>> + if (entry->offset > offset)
>> + node = node->rb_left;
>> + else if (entry->offset < offset)
>> + node = node->rb_right;
>> + else
>> + return entry;
>> + }
>> + return NULL;
>> +}
>> +
>> +/*
>> + * In the case that a entry with the same offset is found, it a pointer to
>> + * the existing entry is stored in dupentry and the function returns -EEXIST
>> +*/
>> +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
>> + struct zswap_entry **dupentry)
>> +{
>> + struct rb_node **link = &root->rb_node, *parent = NULL;
>> + struct zswap_entry *myentry;
>> +
>> + while (*link) {
>> + parent = *link;
>> + myentry = rb_entry(parent, struct zswap_entry, rbnode);
>> + if (myentry->offset > entry->offset)
>> + link = &(*link)->rb_left;
>> + else if (myentry->offset < entry->offset)
>> + link = &(*link)->rb_right;
>> + else {
>> + *dupentry = myentry;
>> + return -EEXIST;
>> + }
>> + }
>> + rb_link_node(&entry->rbnode, parent, link);
>> + rb_insert_color(&entry->rbnode, root);
>> + return 0;
>> +}
>> +
>> +/*********************************
>> +* per-cpu code
>> +**********************************/
>> +static DEFINE_PER_CPU(u8 *, zswap_dstmem);
>> +
>> +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
>> +{
>> + struct crypto_comp *tfm;
>> + u8 *dst;
>> +
>> + switch (action) {
>> + case CPU_UP_PREPARE:
>> + tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
>> + if (IS_ERR(tfm)) {
>> + pr_err("zswap: can't allocate compressor transform\n");
>> + return NOTIFY_BAD;
>> + }
>> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
>> + dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
>> + if (!dst) {
>> + pr_err("zswap: can't allocate compressor buffer\n");
>> + crypto_free_comp(tfm);
>> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
>> + return NOTIFY_BAD;
>> + }
>> + per_cpu(zswap_dstmem, cpu) = dst;
>> + break;
>> + case CPU_DEAD:
>> + case CPU_UP_CANCELED:
>> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
>> + if (tfm) {
>> + crypto_free_comp(tfm);
>> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
>> + }
>> + dst = per_cpu(zswap_dstmem, cpu);
>> + if (dst) {
>> + free_pages((unsigned long)dst, 1);
>> + per_cpu(zswap_dstmem, cpu) = NULL;
>> + }
>> + break;
>> + default:
>> + break;
>> + }
>> + return NOTIFY_OK;
>> +}
>> +
>> +static int zswap_cpu_notifier(struct notifier_block *nb,
>> + unsigned long action, void *pcpu)
>> +{
>> + unsigned long cpu = (unsigned long)pcpu;
>> + return __zswap_cpu_notifier(action, cpu);
>> +}
>> +
>> +static struct notifier_block zswap_cpu_notifier_block = {
>> + .notifier_call = zswap_cpu_notifier
>> +};
>> +
>> +static int zswap_cpu_init(void)
>> +{
>> + unsigned long cpu;
>> +
>> + get_online_cpus();
>> + for_each_online_cpu(cpu)
>> + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
>> + goto cleanup;
>> + register_cpu_notifier(&zswap_cpu_notifier_block);
>> + put_online_cpus();
>> + return 0;
>> +
>> +cleanup:
>> + for_each_online_cpu(cpu)
>> + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
>> + put_online_cpus();
>> + return -ENOMEM;
>> +}
>> +
>> +/*********************************
>> +* zsmalloc callbacks
>> +**********************************/
>> +static mempool_t *zswap_page_pool;
>> +
>> +static u64 zswap_pool_limit_hit;
>> +
>> +static inline unsigned int zswap_max_pool_pages(void)
>> +{
>> + return zswap_max_pool_percent * totalram_pages / 100;
>> +}
>> +
>> +static inline int zswap_page_pool_create(void)
>> +{
>> + zswap_page_pool = mempool_create_page_pool(256, 0);
>
> Could you write down why you select pool to 256?
> If you have a plan, please write down it as TODO.
> I think it could be a function of zswap_max_pool_pages with min/max.
Yes, that would probably be better.
>
> Another question.
>
> What's the benefit of using mempool for zsmalloc?
> As you know, zsmalloc doesn't use mempool as default.
> I guess you see some benefit. if so, zram could be changed.
> If we can change zsmalloc's default scheme to use mempool,
> all of customer of zsmalloc could be enhanced, too.
In the case of zswap, through experimentation, I found that adding a
mempool behind the zsmalloc pool added some elasticity to the pool.
Fewer stores failed if we kept a small reserve of pages around instead
of having to go back to the buddy allocator who, under memory
pressure, is more likely to reject our request.
I don't see this situation being applicable to all zsmalloc users
however. I don't think we want incorporate it directly into zsmalloc
for now. The ability to register custom page alloc/free functions at
pool creation time allows users to do something special, like back
with a mempool, if they want to do that.
>
>> + if (!zswap_page_pool)
>> + return -ENOMEM;
>> + return 0;
>> +}
>> +
>> +static inline void zswap_page_pool_destroy(void)
>> +{
>> + mempool_destroy(zswap_page_pool);
>> +}
>> +
>> +static struct page *zswap_alloc_page(gfp_t flags)
>> +{
>> + struct page *page;
>> +
>> + if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
>> + zswap_pool_limit_hit++;
>> + return NULL;
>> + }
>> + page = mempool_alloc(zswap_page_pool, flags);
>> + if (page)
>> + atomic_inc(&zswap_pool_pages);
>> + return page;
>> +}
>> +
>> +static void zswap_free_page(struct page *page)
>> +{
>> + mempool_free(page, zswap_page_pool);
>> + atomic_dec(&zswap_pool_pages);
>
> Nit.
>
> By semantic, free function can receive NULL argument so
> atomic_dec would be nice to check it before decreasing count.
Are you saying I should check the page != NULL before doing anything
here? If so, I can add that.
>
>> +}
>> +
>> +static struct zs_ops zswap_zs_ops = {
>> + .alloc = zswap_alloc_page,
>> + .free = zswap_free_page
>> +};
>> +
>> +/*********************************
>> +* flush code
>> +**********************************/
>> +static void zswap_end_swap_write(struct bio *bio, int err)
>> +{
>> + end_swap_bio_write(bio, err);
>> + atomic_dec(&zswap_outstanding_flushes);
>> + zswap_flushed_pages++;
>> +}
>> +
>> +/*
>> + * zswap_get_swap_cache_page
>> + *
>> + * This is an adaption of read_swap_cache_async()
>> + *
>> + * If success, page is returned in retpage
>> + * Returns 0 if page was already in the swap cache, page is not locked
>> + * Returns 1 if the new page needs to be populated, page is locked
>> + */
>> +static int zswap_get_swap_cache_page(swp_entry_t entry,
>> + struct page **retpage)
>> +{
>> + struct page *found_page, *new_page = NULL;
>> + int err;
>> +
>> + *retpage = NULL;
>> + do {
>> + /*
>> + * First check the swap cache. Since this is normally
>> + * called after lookup_swap_cache() failed, re-calling
>> + * that would confuse statistics.
>> + */
>> + found_page = find_get_page(&swapper_space, entry.val);
>> + if (found_page)
>> + break;
>> +
>> + /*
>> + * Get a new page to read into from swap.
>> + */
>> + if (!new_page) {
>> + new_page = alloc_page(GFP_KERNEL);
>> + if (!new_page)
>> + break; /* Out of memory */
>> + }
>> +
>> + /*
>> + * call radix_tree_preload() while we can wait.
>> + */
>> + err = radix_tree_preload(GFP_KERNEL);
>> + if (err)
>> + break;
>> +
>> + /*
>> + * Swap entry may have been freed since our caller observed it.
>> + */
>> + err = swapcache_prepare(entry);
>> + if (err == -EEXIST) { /* seems racy */
>> + radix_tree_preload_end();
>> + continue;
>> + }
>> + if (err) { /* swp entry is obsolete ? */
>> + radix_tree_preload_end();
>> + break;
>> + }
>> +
>> + /* May fail (-ENOMEM) if radix-tree node allocation failed. */
>> + __set_page_locked(new_page);
>> + SetPageSwapBacked(new_page);
>> + err = __add_to_swap_cache(new_page, entry);
>> + if (likely(!err)) {
>> + radix_tree_preload_end();
>> + lru_cache_add_anon(new_page);
>> + *retpage = new_page;
>> + return 1;
>> + }
>> + radix_tree_preload_end();
>> + ClearPageSwapBacked(new_page);
>> + __clear_page_locked(new_page);
>> + /*
>> + * add_to_swap_cache() doesn't return -EEXIST, so we can safely
>> + * clear SWAP_HAS_CACHE flag.
>> + */
>> + swapcache_free(entry, NULL);
>> + } while (err != -ENOMEM);
>> +
>> + if (new_page)
>> + page_cache_release(new_page);
>> + if (!found_page)
>> + return -ENOMEM;
>> + *retpage = found_page;
>> + return 0;
>> +}
>> +
>> +static int zswap_flush_entry(struct zswap_entry *entry)
>> +{
>> + unsigned long type = entry->type;
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct page *page;
>> + swp_entry_t swpentry;
>> + u8 *src, *dst;
>> + unsigned int dlen;
>> + int ret, refcount;
>> + struct writeback_control wbc = {
>> + .sync_mode = WB_SYNC_NONE,
>> + };
>> +
>> + /* get/allocate page in the swap cache */
>> + swpentry = swp_entry(type, entry->offset);
>> + ret = zswap_get_swap_cache_page(swpentry, &page);
>> + if (ret < 0)
>> + return ret;
>> + else if (ret) {
>> + /* decompress */
>> + dlen = PAGE_SIZE;
>> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
>> + dst = kmap_atomic(page);
>> + ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
>> + dst, &dlen);
>> + kunmap_atomic(dst);
>> + zs_unmap_object(tree->pool, entry->handle);
>> + BUG_ON(ret);
>> + BUG_ON(dlen != PAGE_SIZE);
>> + SetPageUptodate(page);
>> + } else {
>> + /* page is already in the swap cache, ignore for now */
>> + spin_lock(&tree->lock);
>> + refcount = zswap_entry_put(entry);
>> + spin_unlock(&tree->lock);
>> +
>> + if (likely(refcount))
>> + return 0;
>> +
>> + /* if the refcount is zero, invalidate must have come in */
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +
>> + return 0;
>> + }
>> +
>> + /* start writeback */
>> + SetPageReclaim(page);
>> + /*
>> + * Return value is ignored here because it doesn't change anything
>> + * for us. Page is returned unlocked.
>> + */
>> + (void)__swap_writepage(page, &wbc, zswap_end_swap_write);
>> + page_cache_release(page);
>> + atomic_inc(&zswap_outstanding_flushes);
>> +
>> + /* remove */
>> + spin_lock(&tree->lock);
>> + refcount = zswap_entry_put(entry);
>> + if (refcount > 1) {
>> + /* load in progress, load will free */
>> + spin_unlock(&tree->lock);
>> + return 0;
>> + }
>> + if (refcount == 1)
>> + /* no invalidate yet, remove from rbtree */
>> + rb_erase(&entry->rbnode, &tree->rbroot);
>> + spin_unlock(&tree->lock);
>> +
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +
>> + return 0;
>> +}
>> +
>> +static void zswap_flush_entries(unsigned type, int nr)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry;
>> + int i, ret;
>> +
>> +/*
>> + * This limits is arbitrary for now until a better
>> + * policy can be implemented. This is so we don't
>> + * eat all of RAM decompressing pages for writeback.
>> + */
>> + if (atomic_read(&zswap_outstanding_flushes) >
>> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
>> + return;
>> +
>> + for (i = 0; i < nr; i++) {
>> + /* dequeue from lru */
>> + spin_lock(&tree->lock);
>> + if (list_empty(&tree->lru)) {
>> + spin_unlock(&tree->lock);
>> + break;
>> + }
>> + entry = list_first_entry(&tree->lru,
>> + struct zswap_entry, lru);
>> + list_del(&entry->lru);
>> + zswap_entry_get(entry);
>> + spin_unlock(&tree->lock);
>> + ret = zswap_flush_entry(entry);
>> + if (ret) {
>> + /* put back on the lru */
>> + spin_lock(&tree->lock);
>> + list_add(&entry->lru, &tree->lru);
>> + spin_unlock(&tree->lock);
>> + } else {
>> + if (atomic_read(&zswap_outstanding_flushes) >
>> + ZSWAP_MAX_OUTSTANDING_FLUSHES)
>> + break;
>> + }
>> + }
>> +}
>
> The flush part complexity is very high so we needs careful review.
> I hope you can make the patch step by step from ugly approach to smart one.
> It helps reviewers much.
> If it isn't easy, I will review as it is.
(see comment at top)
>
>> +
>> +/*******************************************
>> +* page pool for temporary compression result
>> +********************************************/
>> +#define ZSWAP_TMPPAGE_POOL_PAGES 16
>> +static LIST_HEAD(zswap_tmppage_list);
>> +static DEFINE_SPINLOCK(zswap_tmppage_lock);
>> +
>> +static void zswap_tmppage_pool_destroy(void)
>> +{
>> + struct page *page, *tmppage;
>> +
>> + spin_lock(&zswap_tmppage_lock);
>> + list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
>> + list_del(&page->lru);
>> + __free_pages(page, 1);
>> + }
>> + spin_unlock(&zswap_tmppage_lock);
>> +}
>> +
>> +static int zswap_tmppage_pool_create(void)
>> +{
>> + int i;
>> + struct page *page;
>> +
>> + for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
>> + page = alloc_pages(GFP_KERNEL, 1);
>> + if (!page) {
>> + zswap_tmppage_pool_destroy();
>> + return -ENOMEM;
>> + }
>> + spin_lock(&zswap_tmppage_lock);
>> + list_add(&page->lru, &zswap_tmppage_list);
>> + spin_unlock(&zswap_tmppage_lock);
>> + }
>> + return 0;
>> +}
>> +
>> +static inline struct page *zswap_tmppage_alloc(void)
>> +{
>> + struct page *page;
>> +
>> + spin_lock(&zswap_tmppage_lock);
>> + if (list_empty(&zswap_tmppage_list)) {
>> + spin_unlock(&zswap_tmppage_lock);
>> + return NULL;
>> + }
>> + page = list_first_entry(&zswap_tmppage_list, struct page, lru);
>> + list_del(&page->lru);
>> + spin_unlock(&zswap_tmppage_lock);
>> + return page;
>> +}
>> +
>> +static inline void zswap_tmppage_free(struct page *page)
>> +{
>> + spin_lock(&zswap_tmppage_lock);
>> + list_add(&page->lru, &zswap_tmppage_list);
>> + spin_unlock(&zswap_tmppage_lock);
>> +}
>> +
>> +/*********************************
>> +* frontswap hooks
>> +**********************************/
>> +/* attempts to compress and store an single page */
>> +static int zswap_frontswap_store(unsigned type, pgoff_t offset, struct page *page)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry, *dupentry;
>> + int ret;
>> + unsigned int dlen = PAGE_SIZE;
>> + unsigned long handle;
>> + char *buf;
>> + u8 *src, *dst, *tmpdst;
>> + struct page *tmppage;
>> + bool flush_attempted = 0;
>> +
>> + if (!tree) {
>> + ret = -ENODEV;
>> + goto reject;
>> + }
>> +
>> + /* compress */
>> + dst = get_cpu_var(zswap_dstmem);
>> + src = kmap_atomic(page);
>> + ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
>> + kunmap_atomic(src);
>> + if (ret) {
>> + ret = -EINVAL;
>> + goto freepage;
>> + }
>> + if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
>> + zswap_reject_compress_poor++;
>> + ret = -E2BIG;
>> + goto freepage;
>> + }
>> +
>> + /* store */
>> + handle = zs_malloc(tree->pool, dlen,
>> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
>> + __GFP_NOWARN);
>> + if (!handle) {
>> + zswap_flush_attempted++;
>> + /*
>> + * Copy compressed buffer out of per-cpu storage so
>> + * we can re-enable preemption.
>> + */
>> + tmppage = zswap_tmppage_alloc();
>> + if (!tmppage) {
>> + zswap_reject_tmppage_fail++;
>> + ret = -ENOMEM;
>> + goto freepage;
>> + }
>> + flush_attempted = 1;
>> + tmpdst = page_address(tmppage);
>> + memcpy(tmpdst, dst, dlen);
>> + dst = tmpdst;
>> + put_cpu_var(zswap_dstmem);
>> +
>> + /* try to free up some space */
>> + /* TODO: replace with more targeted policy */
>> + zswap_flush_entries(type, 16);
>> + /* try again, allowing wait */
>> + handle = zs_malloc(tree->pool, dlen,
>> + __GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
>> + __GFP_NOWARN);
>> + if (!handle) {
>> + /* still no space, fail */
>> + zswap_reject_zsmalloc_fail++;
>> + ret = -ENOMEM;
>> + goto freepage;
>> + }
>> + zswap_saved_by_flush++;
>> + }
>> +
>> + buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
>> + memcpy(buf, dst, dlen);
>> + zs_unmap_object(tree->pool, handle);
>> + if (flush_attempted)
>> + zswap_tmppage_free(tmppage);
>> + else
>> + put_cpu_var(zswap_dstmem);
>> +
>> + /* allocate entry */
>> + entry = zswap_entry_cache_alloc(GFP_KERNEL);
>> + if (!entry) {
>
> zs_free
Good catch!
>
>> + zswap_reject_kmemcache_fail++;
>> + ret = -ENOMEM;
>> + goto reject;
>> + }
>> +
>> + /* populate entry */
>> + entry->type = type;
>> + entry->offset = offset;
>> + entry->handle = handle;
>> + entry->length = dlen;
>> +
>> + /* map */
>> + spin_lock(&tree->lock);
>> + do {
>> + ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
>
> Could you describe why existing entry could be there?
> IIUC, it is caused by delayed swap slot free of VM. Right?
Honestly, I don't know. A comment in the frontswap code said I need
to handle this case, but I'm not sure under what conditions it
happens. I know that it very rarely _does_ happen because I had a bug
during development related to this path.
I'll see if I can get an answer for you.
> Anyway, it would be nice to add comment about it.
>
>
>> + if (ret == -EEXIST) {
>> + zswap_duplicate_entry++;
>> + /* remove from rbtree and lru */
>> + rb_erase(&dupentry->rbnode, &tree->rbroot);
>> + if (dupentry->lru.next != LIST_POISON1)
>
> Why do we need this check? Is there any case entry isn't linked at LRU list?
> Because you already removed it in load part. Right?
Yes, it could be in the process of being loaded or flushed, either one
will have detached the entry from the list.
> Let's add comment about that.
Will do.
> And let's not dependent on LIST_POISON1 of
> list util but use explicit zswap's one.
Good suggestion.
>
>> + list_del(&dupentry->lru);
>> + if (!zswap_entry_put(dupentry)) {
>> + /* free */
>> + zs_free(tree->pool, dupentry->handle);
>> + zswap_entry_cache_free(dupentry);
>> + atomic_dec(&zswap_stored_pages);
>> + }
>> + }
>> + } while (ret == -EEXIST);
>> + list_add_tail(&entry->lru, &tree->lru);
>> + spin_unlock(&tree->lock);
>> +
>> + /* update stats */
>> + atomic_inc(&zswap_stored_pages);
>> +
>> + return 0;
>> +
>> +freepage:
>> + if (flush_attempted)
>> + zswap_tmppage_free(tmppage);
>> + else
>> + put_cpu_var(zswap_dstmem);
>> +reject:
>> + return ret;
>> +}
>> +
>> +/*
>> + * returns 0 if the page was successfully decompressed
>> + * return -1 on entry not found or error
>> +*/
>> +static int zswap_frontswap_load(unsigned type, pgoff_t offset, struct page *page)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry;
>> + u8 *src, *dst;
>> + unsigned int dlen;
>> + int refcount;
>> +
>> + /* find */
>> + spin_lock(&tree->lock);
>> + entry = zswap_rb_search(&tree->rbroot, offset);
>> + if (!entry) {
>> + /* entry was flushed */
>> + spin_unlock(&tree->lock);
>> + return -1;
>> + }
>> + zswap_entry_get(entry);
>> +
>> + /* remove from lru */
>> + if (entry->lru.next != LIST_POISON1)
>
> When do we encounter this case?
> By racing with flush?
Yes.
> Need comment, too.
Yes.
>
>> + list_del(&entry->lru);
>> + spin_unlock(&tree->lock);
>> +
>> + /* decompress */
>> + dlen = PAGE_SIZE;
>> + src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
>> + dst = kmap_atomic(page);
>> + zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
>> + dst, &dlen);
>> + kunmap_atomic(dst);
>> + zs_unmap_object(tree->pool, entry->handle);
>> +
>> + spin_lock(&tree->lock);
>> + refcount = zswap_entry_put(entry);
>> + if (likely(refcount)) {
>> + list_add_tail(&entry->lru, &tree->lru);
>> + spin_unlock(&tree->lock);
>> + return 0;
>> + }
>> + spin_unlock(&tree->lock);
>> +
>> + /*
>> + * We don't have to unlink from the rbtree because zswap_flush_entry()
>> + * or zswap_frontswap_invalidate page() has already done this for us if we
>> + * are the last reference.
>> + */
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +
>> + return 0;
>> +}
>> +
>> +/* invalidates a single page */
>> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct zswap_entry *entry;
>> + int refcount;
>> +
>> + if (!tree)
>
> When do we encounter this case?
Upon second look, I'm not sure that we do. The check in
zswap_frontswap_store() prevents pages from being stored for a
particular swap type if the tree allocation for that type failed
during zswap_frontswap_init().
In that case checking the frontswap_map should prevent any call to
load or invalidate that entry.
I'll make sure. If that is the case, I'll remove this check.
Thanks again for the review!
Seth
>
>> + return;
>> +
>> + /* find */
>> + spin_lock(&tree->lock);
>> + entry = zswap_rb_search(&tree->rbroot, offset);
>> + if (!entry) {
>> + /* entry was flushed */
>> + spin_unlock(&tree->lock);
>> + return;
>> + }
>> +
>> + /* remove from rbtree and lru */
>> + rb_erase(&entry->rbnode, &tree->rbroot);
>> + if (entry->lru.next != LIST_POISON1)
>> + list_del(&entry->lru);
>> + refcount = zswap_entry_put(entry);
>> + spin_unlock(&tree->lock);
>> + if (refcount) {
>> + /* must be flushing */
>> + return;
>> + }
>> +
>> + /* free */
>> + zs_free(tree->pool, entry->handle);
>> + zswap_entry_cache_free(entry);
>> + atomic_dec(&zswap_stored_pages);
>> +}
>> +
>> +/* invalidates all pages for the given swap type */
>> +static void zswap_frontswap_invalidate_area(unsigned type)
>> +{
>> + struct zswap_tree *tree = zswap_trees[type];
>> + struct rb_node *node, *next;
>> + struct zswap_entry *entry;
>> +
>> + if (!tree)
>
> When do we encounter this case?
We can encouter this case.
Since the zswap_frontswap_init() has a void return type, the upper
layer can't know that we failed the tree allocation during swapon.
During a swapoff, it will call zswap_frontswap_invalidate_area(). So
checking !tree is the way we determine if zswap_frontswap_init()
failed at swapon time. If so, there is nothing to do.
>
>> + return;
>> +
>> + /* walk the tree and free everything */
>> + spin_lock(&tree->lock);
>> + node = rb_first(&tree->rbroot);
>> + while (node) {
>> + entry = rb_entry(node, struct zswap_entry, rbnode);
>> + zs_free(tree->pool, entry->handle);
>> + next = rb_next(node);
>> + zswap_entry_cache_free(entry);
>> + node = next;
>> + }
>> + tree->rbroot = RB_ROOT;
>> + INIT_LIST_HEAD(&tree->lru);
>> + spin_unlock(&tree->lock);
>> +}
>> +
>> +/* NOTE: this is called in atomic context from swapon and must not sleep */
>> +static void zswap_frontswap_init(unsigned type)
>> +{
>> + struct zswap_tree *tree;
>> +
>> + tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
>> + if (!tree)
>> + goto err;
>> + tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
>> + if (!tree->pool)
>> + goto freetree;
>> + tree->rbroot = RB_ROOT;
>> + INIT_LIST_HEAD(&tree->lru);
>> + spin_lock_init(&tree->lock);
>> + zswap_trees[type] = tree;
>> + return;
>> +
>> +freetree:
>> + kfree(tree);
>> +err:
>> + pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
>> +}
>> +
>> +static struct frontswap_ops zswap_frontswap_ops = {
>> + .store = zswap_frontswap_store,
>> + .load = zswap_frontswap_load,
>> + .invalidate_page = zswap_frontswap_invalidate_page,
>> + .invalidate_area = zswap_frontswap_invalidate_area,
>> + .init = zswap_frontswap_init
>> +};
>> +
>> +/*********************************
>> +* debugfs functions
>> +**********************************/
>> +#ifdef CONFIG_DEBUG_FS
>> +#include <linux/debugfs.h>
>> +
>> +static struct dentry *zswap_debugfs_root;
>> +
>> +static int __init zswap_debugfs_init(void)
>> +{
>> + if (!debugfs_initialized())
>> + return -ENODEV;
>> +
>> + zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
>> + if (!zswap_debugfs_root)
>> + return -ENOMEM;
>> +
>> + debugfs_create_u64("saved_by_flush", S_IRUGO,
>> + zswap_debugfs_root, &zswap_saved_by_flush);
>> + debugfs_create_u64("pool_limit_hit", S_IRUGO,
>> + zswap_debugfs_root, &zswap_pool_limit_hit);
>> + debugfs_create_u64("reject_flush_attempted", S_IRUGO,
>> + zswap_debugfs_root, &zswap_flush_attempted);
>> + debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_tmppage_fail);
>> + debugfs_create_u64("reject_flush_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_flush_fail);
>> + debugfs_create_u64("reject_zsmalloc_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_zsmalloc_fail);
>> + debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_kmemcache_fail);
>> + debugfs_create_u64("reject_compress_poor", S_IRUGO,
>> + zswap_debugfs_root, &zswap_reject_compress_poor);
>> + debugfs_create_u64("flushed_pages", S_IRUGO,
>> + zswap_debugfs_root, &zswap_flushed_pages);
>> + debugfs_create_u64("duplicate_entry", S_IRUGO,
>> + zswap_debugfs_root, &zswap_duplicate_entry);
>> + debugfs_create_atomic_t("pool_pages", S_IRUGO,
>> + zswap_debugfs_root, &zswap_pool_pages);
>> + debugfs_create_atomic_t("stored_pages", S_IRUGO,
>> + zswap_debugfs_root, &zswap_stored_pages);
>> + debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
>> + zswap_debugfs_root, &zswap_outstanding_flushes);
>> +
>> + return 0;
>> +}
>> +
>> +static void __exit zswap_debugfs_exit(void)
>> +{
>> + if (zswap_debugfs_root)
>> + debugfs_remove_recursive(zswap_debugfs_root);
>> +}
>> +#else
>> +static inline int __init zswap_debugfs_init(void)
>> +{
>> + return 0;
>> +}
>> +
>> +static inline void __exit zswap_debugfs_exit(void) { }
>> +#endif
>> +
>> +/*********************************
>> +* module init and exit
>> +**********************************/
>> +static int __init init_zswap(void)
>> +{
>> + if (!zswap_enabled)
>> + return 0;
>> +
>> + pr_info("loading zswap\n");
>> + if (zswap_entry_cache_create()) {
>> + pr_err("zswap: entry cache creation failed\n");
>> + goto error;
>> + }
>> + if (zswap_page_pool_create()) {
>> + pr_err("zswap: page pool initialization failed\n");
>> + goto pagepoolfail;
>> + }
>> + if (zswap_tmppage_pool_create()) {
>> + pr_err("zswap: workmem pool initialization failed\n");
>> + goto tmppoolfail;
>> + }
>> + if (zswap_comp_init()) {
>> + pr_err("zswap: compressor initialization failed\n");
>> + goto compfail;
>> + }
>> + if (zswap_cpu_init()) {
>> + pr_err("zswap: per-cpu initialization failed\n");
>> + goto pcpufail;
>> + }
>> + frontswap_register_ops(&zswap_frontswap_ops);
>> + if (zswap_debugfs_init())
>> + pr_warn("zswap: debugfs initialization failed\n");
>> + return 0;
>> +pcpufail:
>> + zswap_comp_exit();
>> +compfail:
>> + zswap_tmppage_pool_destroy();
>> +tmppoolfail:
>> + zswap_page_pool_destroy();
>> +pagepoolfail:
>> + zswap_entry_cache_destory();
>> +error:
>> + return -ENOMEM;
>> +}
>> +/* must be late so crypto has time to come up */
>> +late_initcall(init_zswap);
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
>> +MODULE_DESCRIPTION("Compression backend for frontswap pages");
>> --
>> 1.7.9.5
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org. For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
2013-01-29 6:27 ` Minchan Kim
@ 2013-01-29 18:55 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-29 18:55 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On 01/29/2013 12:27 AM, Minchan Kim wrote:
<snip>
> On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
<snip>
>> +/*********************************
>> +* tunables
>> +**********************************/
>> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
>> +static bool zswap_enabled;
>> +module_param_named(enabled, zswap_enabled, bool, 0);
>
> It seems default is disable at the moment?
I completely missed what you were saying before. The comment is
incorrect :) I'll fix it.
Seth
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
@ 2013-01-29 18:55 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-29 18:55 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On 01/29/2013 12:27 AM, Minchan Kim wrote:
<snip>
> On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
<snip>
>> +/*********************************
>> +* tunables
>> +**********************************/
>> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
>> +static bool zswap_enabled;
>> +module_param_named(enabled, zswap_enabled, bool, 0);
>
> It seems default is disable at the moment?
I completely missed what you were saying before. The comment is
incorrect :) I'll fix it.
Seth
--
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 1/6] debugfs: add get/set for atomic types
2013-01-28 21:49 ` Seth Jennings
@ 2013-01-29 20:35 ` Konrad Rzeszutek Wilk
-1 siblings, 0 replies; 38+ messages in thread
From: Konrad Rzeszutek Wilk @ 2013-01-29 20:35 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Dan Magenheimer, Robert Jennings, Jenifer Hopper, Mel Gorman,
Johannes Weiner, Rik van Riel, Larry Woodman,
Benjamin Herrenschmidt, Dave Hansen, linux-mm, linux-kernel,
devel
On Mon, Jan 28, 2013 at 03:49:22PM -0600, Seth Jennings wrote:
> debugfs currently lack the ability to create attributes
> that set/get atomic_t values.
>
> This patch adds support for this through a new
> debugfs_create_atomic_t() function.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> fs/debugfs/file.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/debugfs.h | 2 ++
> 2 files changed, 44 insertions(+)
>
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index c5ca6ae..fa26d5b 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -21,6 +21,7 @@
> #include <linux/debugfs.h>
> #include <linux/io.h>
> #include <linux/slab.h>
> +#include <linux/atomic.h>
>
> static ssize_t default_read_file(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> @@ -403,6 +404,47 @@ struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
> }
> EXPORT_SYMBOL_GPL(debugfs_create_size_t);
>
> +static int debugfs_atomic_t_set(void *data, u64 val)
Should the 'data' be 'atomic_t *' just to make sure nobody messes this
up? Or would that bring too much header changes?
> +{
> + atomic_set((atomic_t *)data, val);
> + return 0;
> +}
> +static int debugfs_atomic_t_get(void *data, u64 *val)
> +{
> + *val = atomic_read((atomic_t *)data);
> + return 0;
> +}
> +DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
> + debugfs_atomic_t_set, "%llu\n");
> +DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL, "%llu\n");
> +DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set, "%llu\n");
> +
> +/**
> + * debugfs_create_atomic_t - create a debugfs file that is used to read and
> + * write an atomic_t value
> + * @name: a pointer to a string containing the name of the file to create.
> + * @mode: the permission that the file should have
> + * @parent: a pointer to the parent dentry for this file. This should be a
> + * directory dentry if set. If this parameter is %NULL, then the
> + * file will be created in the root of the debugfs filesystem.
> + * @value: a pointer to the variable that the file should read to and write
> + * from.
> + */
> +struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
> + struct dentry *parent, atomic_t *value)
> +{
> + /* if there are no write bits set, make read only */
> + if (!(mode & S_IWUGO))
> + return debugfs_create_file(name, mode, parent, value,
> + &fops_atomic_t_ro);
> + /* if there are no read bits set, make write only */
> + if (!(mode & S_IRUGO))
> + return debugfs_create_file(name, mode, parent, value,
> + &fops_atomic_t_wo);
> +
> + return debugfs_create_file(name, mode, parent, value, &fops_atomic_t);
> +}
> +EXPORT_SYMBOL_GPL(debugfs_create_atomic_t);
>
> static ssize_t read_file_bool(struct file *file, char __user *user_buf,
> size_t count, loff_t *ppos)
> diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
> index 66c434f..51fea70 100644
> --- a/include/linux/debugfs.h
> +++ b/include/linux/debugfs.h
> @@ -79,6 +79,8 @@ struct dentry *debugfs_create_x64(const char *name, umode_t mode,
> struct dentry *parent, u64 *value);
> struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
> struct dentry *parent, size_t *value);
> +struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
> + struct dentry *parent, atomic_t *value);
> struct dentry *debugfs_create_bool(const char *name, umode_t mode,
> struct dentry *parent, u32 *value);
>
> --
> 1.7.9.5
>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 1/6] debugfs: add get/set for atomic types
@ 2013-01-29 20:35 ` Konrad Rzeszutek Wilk
0 siblings, 0 replies; 38+ messages in thread
From: Konrad Rzeszutek Wilk @ 2013-01-29 20:35 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Dan Magenheimer, Robert Jennings, Jenifer Hopper, Mel Gorman,
Johannes Weiner, Rik van Riel, Larry Woodman,
Benjamin Herrenschmidt, Dave Hansen, linux-mm, linux-kernel,
devel
On Mon, Jan 28, 2013 at 03:49:22PM -0600, Seth Jennings wrote:
> debugfs currently lack the ability to create attributes
> that set/get atomic_t values.
>
> This patch adds support for this through a new
> debugfs_create_atomic_t() function.
>
> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> fs/debugfs/file.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/debugfs.h | 2 ++
> 2 files changed, 44 insertions(+)
>
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index c5ca6ae..fa26d5b 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -21,6 +21,7 @@
> #include <linux/debugfs.h>
> #include <linux/io.h>
> #include <linux/slab.h>
> +#include <linux/atomic.h>
>
> static ssize_t default_read_file(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> @@ -403,6 +404,47 @@ struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
> }
> EXPORT_SYMBOL_GPL(debugfs_create_size_t);
>
> +static int debugfs_atomic_t_set(void *data, u64 val)
Should the 'data' be 'atomic_t *' just to make sure nobody messes this
up? Or would that bring too much header changes?
> +{
> + atomic_set((atomic_t *)data, val);
> + return 0;
> +}
> +static int debugfs_atomic_t_get(void *data, u64 *val)
> +{
> + *val = atomic_read((atomic_t *)data);
> + return 0;
> +}
> +DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
> + debugfs_atomic_t_set, "%llu\n");
> +DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL, "%llu\n");
> +DEFINE_SIMPLE_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set, "%llu\n");
> +
> +/**
> + * debugfs_create_atomic_t - create a debugfs file that is used to read and
> + * write an atomic_t value
> + * @name: a pointer to a string containing the name of the file to create.
> + * @mode: the permission that the file should have
> + * @parent: a pointer to the parent dentry for this file. This should be a
> + * directory dentry if set. If this parameter is %NULL, then the
> + * file will be created in the root of the debugfs filesystem.
> + * @value: a pointer to the variable that the file should read to and write
> + * from.
> + */
> +struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
> + struct dentry *parent, atomic_t *value)
> +{
> + /* if there are no write bits set, make read only */
> + if (!(mode & S_IWUGO))
> + return debugfs_create_file(name, mode, parent, value,
> + &fops_atomic_t_ro);
> + /* if there are no read bits set, make write only */
> + if (!(mode & S_IRUGO))
> + return debugfs_create_file(name, mode, parent, value,
> + &fops_atomic_t_wo);
> +
> + return debugfs_create_file(name, mode, parent, value, &fops_atomic_t);
> +}
> +EXPORT_SYMBOL_GPL(debugfs_create_atomic_t);
>
> static ssize_t read_file_bool(struct file *file, char __user *user_buf,
> size_t count, loff_t *ppos)
> diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
> index 66c434f..51fea70 100644
> --- a/include/linux/debugfs.h
> +++ b/include/linux/debugfs.h
> @@ -79,6 +79,8 @@ struct dentry *debugfs_create_x64(const char *name, umode_t mode,
> struct dentry *parent, u64 *value);
> struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
> struct dentry *parent, size_t *value);
> +struct dentry *debugfs_create_atomic_t(const char *name, umode_t mode,
> + struct dentry *parent, atomic_t *value);
> struct dentry *debugfs_create_bool(const char *name, umode_t mode,
> struct dentry *parent, u32 *value);
>
> --
> 1.7.9.5
>
--
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Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 1/6] debugfs: add get/set for atomic types
2013-01-29 20:35 ` Konrad Rzeszutek Wilk
@ 2013-01-29 20:49 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-29 20:49 UTC (permalink / raw)
To: Konrad Rzeszutek Wilk
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Dan Magenheimer, Robert Jennings, Jenifer Hopper, Mel Gorman,
Johannes Weiner, Rik van Riel, Larry Woodman,
Benjamin Herrenschmidt, Dave Hansen, linux-mm, linux-kernel,
devel
On 01/29/2013 02:35 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, Jan 28, 2013 at 03:49:22PM -0600, Seth Jennings wrote:
>> debugfs currently lack the ability to create attributes
>> that set/get atomic_t values.
>>
>> This patch adds support for this through a new
>> debugfs_create_atomic_t() function.
>>
>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
>> fs/debugfs/file.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>> include/linux/debugfs.h | 2 ++
>> 2 files changed, 44 insertions(+)
>>
>> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>> index c5ca6ae..fa26d5b 100644
>> --- a/fs/debugfs/file.c
>> +++ b/fs/debugfs/file.c
>> @@ -21,6 +21,7 @@
>> #include <linux/debugfs.h>
>> #include <linux/io.h>
>> #include <linux/slab.h>
>> +#include <linux/atomic.h>
>>
>> static ssize_t default_read_file(struct file *file, char __user *buf,
>> size_t count, loff_t *ppos)
>> @@ -403,6 +404,47 @@ struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
>> }
>> EXPORT_SYMBOL_GPL(debugfs_create_size_t);
>>
>> +static int debugfs_atomic_t_set(void *data, u64 val)
>
> Should the 'data' be 'atomic_t *' just to make sure nobody messes this
> up? Or would that bring too much header changes?
DEFINE_SIMPLE_ATTRIBUTE() uses simple_attr_open() whose signature
requires the argument be a void *. So we can't change it (easily).
Seth
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 1/6] debugfs: add get/set for atomic types
@ 2013-01-29 20:49 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-01-29 20:49 UTC (permalink / raw)
To: Konrad Rzeszutek Wilk
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Minchan Kim,
Dan Magenheimer, Robert Jennings, Jenifer Hopper, Mel Gorman,
Johannes Weiner, Rik van Riel, Larry Woodman,
Benjamin Herrenschmidt, Dave Hansen, linux-mm, linux-kernel,
devel
On 01/29/2013 02:35 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, Jan 28, 2013 at 03:49:22PM -0600, Seth Jennings wrote:
>> debugfs currently lack the ability to create attributes
>> that set/get atomic_t values.
>>
>> This patch adds support for this through a new
>> debugfs_create_atomic_t() function.
>>
>> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
>> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
>> fs/debugfs/file.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>> include/linux/debugfs.h | 2 ++
>> 2 files changed, 44 insertions(+)
>>
>> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>> index c5ca6ae..fa26d5b 100644
>> --- a/fs/debugfs/file.c
>> +++ b/fs/debugfs/file.c
>> @@ -21,6 +21,7 @@
>> #include <linux/debugfs.h>
>> #include <linux/io.h>
>> #include <linux/slab.h>
>> +#include <linux/atomic.h>
>>
>> static ssize_t default_read_file(struct file *file, char __user *buf,
>> size_t count, loff_t *ppos)
>> @@ -403,6 +404,47 @@ struct dentry *debugfs_create_size_t(const char *name, umode_t mode,
>> }
>> EXPORT_SYMBOL_GPL(debugfs_create_size_t);
>>
>> +static int debugfs_atomic_t_set(void *data, u64 val)
>
> Should the 'data' be 'atomic_t *' just to make sure nobody messes this
> up? Or would that bring too much header changes?
DEFINE_SIMPLE_ATTRIBUTE() uses simple_attr_open() whose signature
requires the argument be a void *. So we can't change it (easily).
Seth
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
2013-01-29 17:26 ` Seth Jennings
@ 2013-01-30 4:44 ` Minchan Kim
-1 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-30 4:44 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Tue, Jan 29, 2013 at 11:26:48AM -0600, Seth Jennings wrote:
> On 01/29/2013 12:27 AM, Minchan Kim wrote:
> > First feeling is it's simple and nice approach.
> > Although we have some problems to decide policy, it could solve by later patch
> > so I hope we make basic infrasture more solid by lots of comment.
>
> Thanks very much for the review!
>
> >
> > There are two things to review hard.
> >
> > 1. data structure life - when any data structure is died by whom?
> > Please write down it in changelog or header of zswap.c
> >
> > 2. Flush routine - I hope it would be nice to separate it as another
> > incremental patches if it is possible. If it's impossible, let's add
> > lots of words.
>
> It seems like it would be difficult to break the flushing
> functionality into it's own patch, but I can start the process and
> see. As long as people keep in mind that some of the design rationale
> in the version without the flush code is dictated by the addition of
> the flush code.
>
> But yes, more comments.
>
> > On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
> >> zswap is a thin compression backend for frontswap. It receives
> >> pages from frontswap and attempts to store them in a compressed
> >> memory pool, resulting in an effective partial memory reclaim and
> >> dramatically reduced swap device I/O.
> >>
> >> Additional, in most cases, pages can be retrieved from this
> >> compressed store much more quickly than reading from tradition
> >> swap devices resulting in faster performance for many workloads.
> >>
> >> This patch adds the zswap driver to mm/
> >>
> >> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> >> ---
> >> mm/Kconfig | 15 +
> >> mm/Makefile | 1 +
> >> mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> 3 files changed, 1089 insertions(+)
> >> create mode 100644 mm/zswap.c
> >>
> >> diff --git a/mm/Kconfig b/mm/Kconfig
> >> index 278e3ab..14b9acb 100644
> >> --- a/mm/Kconfig
> >> +++ b/mm/Kconfig
> >> @@ -446,3 +446,18 @@ config FRONTSWAP
> >> and swap data is stored as normal on the matching swap device.
> >>
> >> If unsure, say Y to enable frontswap.
> >> +
> >> +config ZSWAP
> >> + bool "In-kernel swap page compression"
> >> + depends on FRONTSWAP && CRYPTO
> >
> > Couldn't we support CRYPTO optionally?
>
> No. zswap depends on the cryptographic API for access to the
> compression modules.
I meant I don't want to enable CONFIG_CRYPTO for just using zswap.
In case of zram, we didn't need it.
Is there any reason we must use encryption for using zswap?
>
> >
> >> + select CRYPTO_LZO
> >> + select ZSMALLOC
> >> + default n
> >> + help
> >> + Zswap is a backend for the frontswap mechanism in the VMM.
> >> + It receives pages from frontswap and attempts to store them
> >> + in a compressed memory pool, resulting in an effective
> >> + partial memory reclaim. In addition, pages and be retrieved
> >> + from this compressed store much faster than most tradition
> >> + swap devices resulting in reduced I/O and faster performance
> >> + for many workloads.
> >> index 3a46287..1b1ed5c 100644
> >> --- a/mm/Makefile
> >> +++ b/mm/Makefile
> >> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
> >> obj-$(CONFIG_BOUNCE) += bounce.o
> >> obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
> >> obj-$(CONFIG_FRONTSWAP) += frontswap.o
> >> +obj-$(CONFIG_ZSWAP) += zswap.o
> >> obj-$(CONFIG_HAS_DMA) += dmapool.o
> >> obj-$(CONFIG_HUGETLBFS) += hugetlb.o
> >> obj-$(CONFIG_NUMA) += mempolicy.o
> >> diff --git a/mm/zswap.c b/mm/zswap.c
> >> new file mode 100644
> >> index 0000000..050b6db
> >> --- /dev/null
> >> +++ b/mm/zswap.c
> >> @@ -0,0 +1,1073 @@
> >> +/*
> >> + * zswap-drv.c - zswap driver file
> >> + *
> >> + * zswap is a backend for frontswap that takes pages that are in the
> >> + * process of being swapped out and attempts to compress them and store
> >> + * them in a RAM-based memory pool. This results in a significant I/O
> >> + * reduction on the real swap device and, in the case of a slow swap
> >> + * device, can also improve workload performance.
> >> + *
> >> + * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
> >> + *
> >> + * This program is free software; you can redistribute it and/or
> >> + * modify it under the terms of the GNU General Public License
> >> + * as published by the Free Software Foundation; either version 2
> >> + * of the License, or (at your option) any later version.
> >> + *
> >> + * This program is distributed in the hope that it will be useful,
> >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> >> + * GNU General Public License for more details.
> >> +*/
> >> +
> >> +#include <linux/module.h>
> >> +#include <linux/cpu.h>
> >> +#include <linux/highmem.h>
> >> +#include <linux/slab.h>
> >> +#include <linux/spinlock.h>
> >> +#include <linux/types.h>
> >> +#include <linux/atomic.h>
> >> +#include <linux/frontswap.h>
> >> +#include <linux/rbtree.h>
> >> +#include <linux/swap.h>
> >> +#include <linux/crypto.h>
> >> +#include <linux/mempool.h>
> >> +#include <linux/zsmalloc.h>
> >> +
> >> +#include <linux/mm_types.h>
> >> +#include <linux/page-flags.h>
> >> +#include <linux/swapops.h>
> >> +#include <linux/writeback.h>
> >> +#include <linux/pagemap.h>
> >> +
> >> +/*********************************
> >> +* statistics
> >> +**********************************/
> >> +/* Number of memory pages used by the compressed pool */
> >> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
> >> +/* The number of compressed pages currently stored in zswap */
> >> +static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
> >> +/* The number of outstanding pages awaiting writeback */
> >> +static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
> >> +
> >> +/*
> >> + * The statistics below are not protected from concurrent access for
> >> + * performance reasons so they may not be a 100% accurate. However,
> >> + * the do provide useful information on roughly how many times a
> >> + * certain event is occurring.
> >> +*/
> >> +static u64 zswap_flushed_pages;
> >> +static u64 zswap_reject_compress_poor;
> >> +static u64 zswap_flush_attempted;
> >> +static u64 zswap_reject_tmppage_fail;
> >> +static u64 zswap_reject_flush_fail;
> >> +static u64 zswap_reject_zsmalloc_fail;
> >> +static u64 zswap_reject_kmemcache_fail;
> >> +static u64 zswap_saved_by_flush;
> >> +static u64 zswap_duplicate_entry;
> >> +
> >> +/*********************************
> >> +* tunables
> >> +**********************************/
> >> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
> >> +static bool zswap_enabled;
> >> +module_param_named(enabled, zswap_enabled, bool, 0);
> >
> > It seems default is disable at the moment?
>
> Yes, that's right. While zswap should be always-on safe (i.e. no
> impact if swap isn't being used), I thought this would be the safe way
> for now.
>
> >
> >> +
> >> +/* Compressor to be used by zswap (fixed at boot for now) */
> >> +#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> >> +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> >> +module_param_named(compressor, zswap_compressor, charp, 0);
> >> +
> >> +/* The maximum percentage of memory that the compressed pool can occupy */
> >> +static unsigned int zswap_max_pool_percent = 20;
> >> +module_param_named(max_pool_percent,
> >> + zswap_max_pool_percent, uint, 0644);
> >> +
> >> +/*
> >> + * Maximum compression ratio, as as percentage, for an acceptable
> >> + * compressed page. Any pages that do not compress by at least
> >> + * this ratio will be rejected.
> >> +*/
> >> +static unsigned int zswap_max_compression_ratio = 80;
> >> +module_param_named(max_compression_ratio,
> >> + zswap_max_compression_ratio, uint, 0644);
> >> +
> >> +/*
> >> + * Maximum number of outstanding flushes allowed at any given time.
> >> + * This is to prevent decompressing an unbounded number of compressed
> >> + * pages into the swap cache all at once, and to help with writeback
> >> + * congestion.
> >> +*/
> >> +#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
> >> +
> >> +/*********************************
> >> +* compression functions
> >> +**********************************/
> >> +/* per-cpu compression transforms */
> >> +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
> >> +
> >> +enum comp_op {
> >> + ZSWAP_COMPOP_COMPRESS,
> >> + ZSWAP_COMPOP_DECOMPRESS
> >> +};
> >> +
> >> +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
> >> + u8 *dst, unsigned int *dlen)
> >> +{
> >> + struct crypto_comp *tfm;
> >> + int ret;
> >> +
> >> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
> >> + switch (op) {
> >> + case ZSWAP_COMPOP_COMPRESS:
> >> + ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
> >> + break;
> >> + case ZSWAP_COMPOP_DECOMPRESS:
> >> + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
> >> + break;
> >> + default:
> >> + ret = -EINVAL;
> >> + }
> >> +
> >> + put_cpu();
> >> + return ret;
> >> +}
> >> +
> >> +static int __init zswap_comp_init(void)
> >> +{
> >> + if (!crypto_has_comp(zswap_compressor, 0, 0)) {
> >> + pr_info("zswap: %s compressor not available\n",
> >> + zswap_compressor);
> >> + /* fall back to default compressor */
> >> + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> >> + if (!crypto_has_comp(zswap_compressor, 0, 0))
> >> + /* can't even load the default compressor */
> >> + return -ENODEV;
> >> + }
> >> + pr_info("zswap: using %s compressor\n", zswap_compressor);
> >> +
> >> + /* alloc percpu transforms */
> >> + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
> >> + if (!zswap_comp_pcpu_tfms)
> >> + return -ENOMEM;
> >> + return 0;
> >> +}
> >> +
> >> +static void zswap_comp_exit(void)
> >> +{
> >> + /* free percpu transforms */
> >> + if (zswap_comp_pcpu_tfms)
> >> + free_percpu(zswap_comp_pcpu_tfms);
> >> +}
> >> +
> >> +/*********************************
> >> +* data structures
> >> +**********************************/
> >> +struct zswap_entry {
> >> + struct rb_node rbnode;
> >> + struct list_head lru;
> >> + int refcount;
> >> + unsigned type;
> >> + pgoff_t offset;
> >> + unsigned long handle;
> >> + unsigned int length;
> >> +};
> >> +
> >> +/*
> >> + * The tree lock in the zswap_tree struct protects a few things:
> >> + * - the rbtree
> >> + * - the lru list
> >> + * - the refcount field of each entry in the tree
> >> + */
> >> +struct zswap_tree {
> >> + struct rb_root rbroot;
> >> + struct list_head lru;
> >> + spinlock_t lock;
> >> + struct zs_pool *pool;
> >> +};
> >> +
> >> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
> >> +
> >> +/*********************************
> >> +* zswap entry functions
> >> +**********************************/
> >> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
> >> +static struct kmem_cache *zswap_entry_cache;
> >> +
> >> +static inline int zswap_entry_cache_create(void)
> >> +{
> >> + zswap_entry_cache =
> >> + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
> >> + sizeof(struct zswap_entry), 0, 0, NULL);
> >> + return (zswap_entry_cache == NULL);
> >> +}
> >> +
> >> +static inline void zswap_entry_cache_destory(void)
> >> +{
> >> + kmem_cache_destroy(zswap_entry_cache);
> >> +}
> >> +
> >> +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
> >> +{
> >> + struct zswap_entry *entry;
> >> + entry = kmem_cache_alloc(zswap_entry_cache, gfp);
> >> + if (!entry)
> >> + return NULL;
> >> + INIT_LIST_HEAD(&entry->lru);
> >> + entry->refcount = 1;
> >> + return entry;
> >> +}
> >> +
> >> +static inline void zswap_entry_cache_free(struct zswap_entry *entry)
> >> +{
> >> + kmem_cache_free(zswap_entry_cache, entry);
> >> +}
> >> +
> >> +static inline void zswap_entry_get(struct zswap_entry *entry)
> >> +{
> >> + entry->refcount++;
> >> +}
> >> +
> >> +static inline int zswap_entry_put(struct zswap_entry *entry)
> >> +{
> >> + entry->refcount--;
> >> + return entry->refcount;
> >> +}
> >> +
> >> +/*********************************
> >> +* rbtree functions
> >> +**********************************/
> >> +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
> >> +{
> >> + struct rb_node *node = root->rb_node;
> >> + struct zswap_entry *entry;
> >> +
> >> + while (node) {
> >> + entry = rb_entry(node, struct zswap_entry, rbnode);
> >> + if (entry->offset > offset)
> >> + node = node->rb_left;
> >> + else if (entry->offset < offset)
> >> + node = node->rb_right;
> >> + else
> >> + return entry;
> >> + }
> >> + return NULL;
> >> +}
> >> +
> >> +/*
> >> + * In the case that a entry with the same offset is found, it a pointer to
> >> + * the existing entry is stored in dupentry and the function returns -EEXIST
> >> +*/
> >> +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
> >> + struct zswap_entry **dupentry)
> >> +{
> >> + struct rb_node **link = &root->rb_node, *parent = NULL;
> >> + struct zswap_entry *myentry;
> >> +
> >> + while (*link) {
> >> + parent = *link;
> >> + myentry = rb_entry(parent, struct zswap_entry, rbnode);
> >> + if (myentry->offset > entry->offset)
> >> + link = &(*link)->rb_left;
> >> + else if (myentry->offset < entry->offset)
> >> + link = &(*link)->rb_right;
> >> + else {
> >> + *dupentry = myentry;
> >> + return -EEXIST;
> >> + }
> >> + }
> >> + rb_link_node(&entry->rbnode, parent, link);
> >> + rb_insert_color(&entry->rbnode, root);
> >> + return 0;
> >> +}
> >> +
> >> +/*********************************
> >> +* per-cpu code
> >> +**********************************/
> >> +static DEFINE_PER_CPU(u8 *, zswap_dstmem);
> >> +
> >> +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
> >> +{
> >> + struct crypto_comp *tfm;
> >> + u8 *dst;
> >> +
> >> + switch (action) {
> >> + case CPU_UP_PREPARE:
> >> + tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
> >> + if (IS_ERR(tfm)) {
> >> + pr_err("zswap: can't allocate compressor transform\n");
> >> + return NOTIFY_BAD;
> >> + }
> >> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
> >> + dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
> >> + if (!dst) {
> >> + pr_err("zswap: can't allocate compressor buffer\n");
> >> + crypto_free_comp(tfm);
> >> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> >> + return NOTIFY_BAD;
> >> + }
> >> + per_cpu(zswap_dstmem, cpu) = dst;
> >> + break;
> >> + case CPU_DEAD:
> >> + case CPU_UP_CANCELED:
> >> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
> >> + if (tfm) {
> >> + crypto_free_comp(tfm);
> >> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> >> + }
> >> + dst = per_cpu(zswap_dstmem, cpu);
> >> + if (dst) {
> >> + free_pages((unsigned long)dst, 1);
> >> + per_cpu(zswap_dstmem, cpu) = NULL;
> >> + }
> >> + break;
> >> + default:
> >> + break;
> >> + }
> >> + return NOTIFY_OK;
> >> +}
> >> +
> >> +static int zswap_cpu_notifier(struct notifier_block *nb,
> >> + unsigned long action, void *pcpu)
> >> +{
> >> + unsigned long cpu = (unsigned long)pcpu;
> >> + return __zswap_cpu_notifier(action, cpu);
> >> +}
> >> +
> >> +static struct notifier_block zswap_cpu_notifier_block = {
> >> + .notifier_call = zswap_cpu_notifier
> >> +};
> >> +
> >> +static int zswap_cpu_init(void)
> >> +{
> >> + unsigned long cpu;
> >> +
> >> + get_online_cpus();
> >> + for_each_online_cpu(cpu)
> >> + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
> >> + goto cleanup;
> >> + register_cpu_notifier(&zswap_cpu_notifier_block);
> >> + put_online_cpus();
> >> + return 0;
> >> +
> >> +cleanup:
> >> + for_each_online_cpu(cpu)
> >> + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
> >> + put_online_cpus();
> >> + return -ENOMEM;
> >> +}
> >> +
> >> +/*********************************
> >> +* zsmalloc callbacks
> >> +**********************************/
> >> +static mempool_t *zswap_page_pool;
> >> +
> >> +static u64 zswap_pool_limit_hit;
> >> +
> >> +static inline unsigned int zswap_max_pool_pages(void)
> >> +{
> >> + return zswap_max_pool_percent * totalram_pages / 100;
> >> +}
> >> +
> >> +static inline int zswap_page_pool_create(void)
> >> +{
> >> + zswap_page_pool = mempool_create_page_pool(256, 0);
> >
> > Could you write down why you select pool to 256?
> > If you have a plan, please write down it as TODO.
> > I think it could be a function of zswap_max_pool_pages with min/max.
>
> Yes, that would probably be better.
>
> >
> > Another question.
> >
> > What's the benefit of using mempool for zsmalloc?
> > As you know, zsmalloc doesn't use mempool as default.
> > I guess you see some benefit. if so, zram could be changed.
> > If we can change zsmalloc's default scheme to use mempool,
> > all of customer of zsmalloc could be enhanced, too.
>
> In the case of zswap, through experimentation, I found that adding a
> mempool behind the zsmalloc pool added some elasticity to the pool.
> Fewer stores failed if we kept a small reserve of pages around instead
> of having to go back to the buddy allocator who, under memory
> pressure, is more likely to reject our request.
>
> I don't see this situation being applicable to all zsmalloc users
> however. I don't think we want incorporate it directly into zsmalloc
> for now. The ability to register custom page alloc/free functions at
> pool creation time allows users to do something special, like back
> with a mempool, if they want to do that.
Okay. I'd like to test this approach with zram later and if it makes sense
for everything, I will try to change zsmalloc's inside.
Thanks!
--
Kind regards,
Minchan Kim
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
@ 2013-01-30 4:44 ` Minchan Kim
0 siblings, 0 replies; 38+ messages in thread
From: Minchan Kim @ 2013-01-30 4:44 UTC (permalink / raw)
To: Seth Jennings
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Rzeszutek Wilk, Dan Magenheimer, Robert Jennings,
Jenifer Hopper, Mel Gorman, Johannes Weiner, Rik van Riel,
Larry Woodman, Benjamin Herrenschmidt, Dave Hansen, linux-mm,
linux-kernel, devel
On Tue, Jan 29, 2013 at 11:26:48AM -0600, Seth Jennings wrote:
> On 01/29/2013 12:27 AM, Minchan Kim wrote:
> > First feeling is it's simple and nice approach.
> > Although we have some problems to decide policy, it could solve by later patch
> > so I hope we make basic infrasture more solid by lots of comment.
>
> Thanks very much for the review!
>
> >
> > There are two things to review hard.
> >
> > 1. data structure life - when any data structure is died by whom?
> > Please write down it in changelog or header of zswap.c
> >
> > 2. Flush routine - I hope it would be nice to separate it as another
> > incremental patches if it is possible. If it's impossible, let's add
> > lots of words.
>
> It seems like it would be difficult to break the flushing
> functionality into it's own patch, but I can start the process and
> see. As long as people keep in mind that some of the design rationale
> in the version without the flush code is dictated by the addition of
> the flush code.
>
> But yes, more comments.
>
> > On Mon, Jan 28, 2013 at 03:49:26PM -0600, Seth Jennings wrote:
> >> zswap is a thin compression backend for frontswap. It receives
> >> pages from frontswap and attempts to store them in a compressed
> >> memory pool, resulting in an effective partial memory reclaim and
> >> dramatically reduced swap device I/O.
> >>
> >> Additional, in most cases, pages can be retrieved from this
> >> compressed store much more quickly than reading from tradition
> >> swap devices resulting in faster performance for many workloads.
> >>
> >> This patch adds the zswap driver to mm/
> >>
> >> Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
> >> ---
> >> mm/Kconfig | 15 +
> >> mm/Makefile | 1 +
> >> mm/zswap.c | 1073 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> 3 files changed, 1089 insertions(+)
> >> create mode 100644 mm/zswap.c
> >>
> >> diff --git a/mm/Kconfig b/mm/Kconfig
> >> index 278e3ab..14b9acb 100644
> >> --- a/mm/Kconfig
> >> +++ b/mm/Kconfig
> >> @@ -446,3 +446,18 @@ config FRONTSWAP
> >> and swap data is stored as normal on the matching swap device.
> >>
> >> If unsure, say Y to enable frontswap.
> >> +
> >> +config ZSWAP
> >> + bool "In-kernel swap page compression"
> >> + depends on FRONTSWAP && CRYPTO
> >
> > Couldn't we support CRYPTO optionally?
>
> No. zswap depends on the cryptographic API for access to the
> compression modules.
I meant I don't want to enable CONFIG_CRYPTO for just using zswap.
In case of zram, we didn't need it.
Is there any reason we must use encryption for using zswap?
>
> >
> >> + select CRYPTO_LZO
> >> + select ZSMALLOC
> >> + default n
> >> + help
> >> + Zswap is a backend for the frontswap mechanism in the VMM.
> >> + It receives pages from frontswap and attempts to store them
> >> + in a compressed memory pool, resulting in an effective
> >> + partial memory reclaim. In addition, pages and be retrieved
> >> + from this compressed store much faster than most tradition
> >> + swap devices resulting in reduced I/O and faster performance
> >> + for many workloads.
> >> index 3a46287..1b1ed5c 100644
> >> --- a/mm/Makefile
> >> +++ b/mm/Makefile
> >> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
> >> obj-$(CONFIG_BOUNCE) += bounce.o
> >> obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
> >> obj-$(CONFIG_FRONTSWAP) += frontswap.o
> >> +obj-$(CONFIG_ZSWAP) += zswap.o
> >> obj-$(CONFIG_HAS_DMA) += dmapool.o
> >> obj-$(CONFIG_HUGETLBFS) += hugetlb.o
> >> obj-$(CONFIG_NUMA) += mempolicy.o
> >> diff --git a/mm/zswap.c b/mm/zswap.c
> >> new file mode 100644
> >> index 0000000..050b6db
> >> --- /dev/null
> >> +++ b/mm/zswap.c
> >> @@ -0,0 +1,1073 @@
> >> +/*
> >> + * zswap-drv.c - zswap driver file
> >> + *
> >> + * zswap is a backend for frontswap that takes pages that are in the
> >> + * process of being swapped out and attempts to compress them and store
> >> + * them in a RAM-based memory pool. This results in a significant I/O
> >> + * reduction on the real swap device and, in the case of a slow swap
> >> + * device, can also improve workload performance.
> >> + *
> >> + * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
> >> + *
> >> + * This program is free software; you can redistribute it and/or
> >> + * modify it under the terms of the GNU General Public License
> >> + * as published by the Free Software Foundation; either version 2
> >> + * of the License, or (at your option) any later version.
> >> + *
> >> + * This program is distributed in the hope that it will be useful,
> >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> >> + * GNU General Public License for more details.
> >> +*/
> >> +
> >> +#include <linux/module.h>
> >> +#include <linux/cpu.h>
> >> +#include <linux/highmem.h>
> >> +#include <linux/slab.h>
> >> +#include <linux/spinlock.h>
> >> +#include <linux/types.h>
> >> +#include <linux/atomic.h>
> >> +#include <linux/frontswap.h>
> >> +#include <linux/rbtree.h>
> >> +#include <linux/swap.h>
> >> +#include <linux/crypto.h>
> >> +#include <linux/mempool.h>
> >> +#include <linux/zsmalloc.h>
> >> +
> >> +#include <linux/mm_types.h>
> >> +#include <linux/page-flags.h>
> >> +#include <linux/swapops.h>
> >> +#include <linux/writeback.h>
> >> +#include <linux/pagemap.h>
> >> +
> >> +/*********************************
> >> +* statistics
> >> +**********************************/
> >> +/* Number of memory pages used by the compressed pool */
> >> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
> >> +/* The number of compressed pages currently stored in zswap */
> >> +static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
> >> +/* The number of outstanding pages awaiting writeback */
> >> +static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
> >> +
> >> +/*
> >> + * The statistics below are not protected from concurrent access for
> >> + * performance reasons so they may not be a 100% accurate. However,
> >> + * the do provide useful information on roughly how many times a
> >> + * certain event is occurring.
> >> +*/
> >> +static u64 zswap_flushed_pages;
> >> +static u64 zswap_reject_compress_poor;
> >> +static u64 zswap_flush_attempted;
> >> +static u64 zswap_reject_tmppage_fail;
> >> +static u64 zswap_reject_flush_fail;
> >> +static u64 zswap_reject_zsmalloc_fail;
> >> +static u64 zswap_reject_kmemcache_fail;
> >> +static u64 zswap_saved_by_flush;
> >> +static u64 zswap_duplicate_entry;
> >> +
> >> +/*********************************
> >> +* tunables
> >> +**********************************/
> >> +/* Enable/disable zswap (enabled by default, fixed at boot for now) */
> >> +static bool zswap_enabled;
> >> +module_param_named(enabled, zswap_enabled, bool, 0);
> >
> > It seems default is disable at the moment?
>
> Yes, that's right. While zswap should be always-on safe (i.e. no
> impact if swap isn't being used), I thought this would be the safe way
> for now.
>
> >
> >> +
> >> +/* Compressor to be used by zswap (fixed at boot for now) */
> >> +#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> >> +static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> >> +module_param_named(compressor, zswap_compressor, charp, 0);
> >> +
> >> +/* The maximum percentage of memory that the compressed pool can occupy */
> >> +static unsigned int zswap_max_pool_percent = 20;
> >> +module_param_named(max_pool_percent,
> >> + zswap_max_pool_percent, uint, 0644);
> >> +
> >> +/*
> >> + * Maximum compression ratio, as as percentage, for an acceptable
> >> + * compressed page. Any pages that do not compress by at least
> >> + * this ratio will be rejected.
> >> +*/
> >> +static unsigned int zswap_max_compression_ratio = 80;
> >> +module_param_named(max_compression_ratio,
> >> + zswap_max_compression_ratio, uint, 0644);
> >> +
> >> +/*
> >> + * Maximum number of outstanding flushes allowed at any given time.
> >> + * This is to prevent decompressing an unbounded number of compressed
> >> + * pages into the swap cache all at once, and to help with writeback
> >> + * congestion.
> >> +*/
> >> +#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
> >> +
> >> +/*********************************
> >> +* compression functions
> >> +**********************************/
> >> +/* per-cpu compression transforms */
> >> +static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
> >> +
> >> +enum comp_op {
> >> + ZSWAP_COMPOP_COMPRESS,
> >> + ZSWAP_COMPOP_DECOMPRESS
> >> +};
> >> +
> >> +static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
> >> + u8 *dst, unsigned int *dlen)
> >> +{
> >> + struct crypto_comp *tfm;
> >> + int ret;
> >> +
> >> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
> >> + switch (op) {
> >> + case ZSWAP_COMPOP_COMPRESS:
> >> + ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
> >> + break;
> >> + case ZSWAP_COMPOP_DECOMPRESS:
> >> + ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
> >> + break;
> >> + default:
> >> + ret = -EINVAL;
> >> + }
> >> +
> >> + put_cpu();
> >> + return ret;
> >> +}
> >> +
> >> +static int __init zswap_comp_init(void)
> >> +{
> >> + if (!crypto_has_comp(zswap_compressor, 0, 0)) {
> >> + pr_info("zswap: %s compressor not available\n",
> >> + zswap_compressor);
> >> + /* fall back to default compressor */
> >> + zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> >> + if (!crypto_has_comp(zswap_compressor, 0, 0))
> >> + /* can't even load the default compressor */
> >> + return -ENODEV;
> >> + }
> >> + pr_info("zswap: using %s compressor\n", zswap_compressor);
> >> +
> >> + /* alloc percpu transforms */
> >> + zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
> >> + if (!zswap_comp_pcpu_tfms)
> >> + return -ENOMEM;
> >> + return 0;
> >> +}
> >> +
> >> +static void zswap_comp_exit(void)
> >> +{
> >> + /* free percpu transforms */
> >> + if (zswap_comp_pcpu_tfms)
> >> + free_percpu(zswap_comp_pcpu_tfms);
> >> +}
> >> +
> >> +/*********************************
> >> +* data structures
> >> +**********************************/
> >> +struct zswap_entry {
> >> + struct rb_node rbnode;
> >> + struct list_head lru;
> >> + int refcount;
> >> + unsigned type;
> >> + pgoff_t offset;
> >> + unsigned long handle;
> >> + unsigned int length;
> >> +};
> >> +
> >> +/*
> >> + * The tree lock in the zswap_tree struct protects a few things:
> >> + * - the rbtree
> >> + * - the lru list
> >> + * - the refcount field of each entry in the tree
> >> + */
> >> +struct zswap_tree {
> >> + struct rb_root rbroot;
> >> + struct list_head lru;
> >> + spinlock_t lock;
> >> + struct zs_pool *pool;
> >> +};
> >> +
> >> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
> >> +
> >> +/*********************************
> >> +* zswap entry functions
> >> +**********************************/
> >> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
> >> +static struct kmem_cache *zswap_entry_cache;
> >> +
> >> +static inline int zswap_entry_cache_create(void)
> >> +{
> >> + zswap_entry_cache =
> >> + kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
> >> + sizeof(struct zswap_entry), 0, 0, NULL);
> >> + return (zswap_entry_cache == NULL);
> >> +}
> >> +
> >> +static inline void zswap_entry_cache_destory(void)
> >> +{
> >> + kmem_cache_destroy(zswap_entry_cache);
> >> +}
> >> +
> >> +static inline struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
> >> +{
> >> + struct zswap_entry *entry;
> >> + entry = kmem_cache_alloc(zswap_entry_cache, gfp);
> >> + if (!entry)
> >> + return NULL;
> >> + INIT_LIST_HEAD(&entry->lru);
> >> + entry->refcount = 1;
> >> + return entry;
> >> +}
> >> +
> >> +static inline void zswap_entry_cache_free(struct zswap_entry *entry)
> >> +{
> >> + kmem_cache_free(zswap_entry_cache, entry);
> >> +}
> >> +
> >> +static inline void zswap_entry_get(struct zswap_entry *entry)
> >> +{
> >> + entry->refcount++;
> >> +}
> >> +
> >> +static inline int zswap_entry_put(struct zswap_entry *entry)
> >> +{
> >> + entry->refcount--;
> >> + return entry->refcount;
> >> +}
> >> +
> >> +/*********************************
> >> +* rbtree functions
> >> +**********************************/
> >> +static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
> >> +{
> >> + struct rb_node *node = root->rb_node;
> >> + struct zswap_entry *entry;
> >> +
> >> + while (node) {
> >> + entry = rb_entry(node, struct zswap_entry, rbnode);
> >> + if (entry->offset > offset)
> >> + node = node->rb_left;
> >> + else if (entry->offset < offset)
> >> + node = node->rb_right;
> >> + else
> >> + return entry;
> >> + }
> >> + return NULL;
> >> +}
> >> +
> >> +/*
> >> + * In the case that a entry with the same offset is found, it a pointer to
> >> + * the existing entry is stored in dupentry and the function returns -EEXIST
> >> +*/
> >> +static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
> >> + struct zswap_entry **dupentry)
> >> +{
> >> + struct rb_node **link = &root->rb_node, *parent = NULL;
> >> + struct zswap_entry *myentry;
> >> +
> >> + while (*link) {
> >> + parent = *link;
> >> + myentry = rb_entry(parent, struct zswap_entry, rbnode);
> >> + if (myentry->offset > entry->offset)
> >> + link = &(*link)->rb_left;
> >> + else if (myentry->offset < entry->offset)
> >> + link = &(*link)->rb_right;
> >> + else {
> >> + *dupentry = myentry;
> >> + return -EEXIST;
> >> + }
> >> + }
> >> + rb_link_node(&entry->rbnode, parent, link);
> >> + rb_insert_color(&entry->rbnode, root);
> >> + return 0;
> >> +}
> >> +
> >> +/*********************************
> >> +* per-cpu code
> >> +**********************************/
> >> +static DEFINE_PER_CPU(u8 *, zswap_dstmem);
> >> +
> >> +static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
> >> +{
> >> + struct crypto_comp *tfm;
> >> + u8 *dst;
> >> +
> >> + switch (action) {
> >> + case CPU_UP_PREPARE:
> >> + tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
> >> + if (IS_ERR(tfm)) {
> >> + pr_err("zswap: can't allocate compressor transform\n");
> >> + return NOTIFY_BAD;
> >> + }
> >> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
> >> + dst = (u8 *)__get_free_pages(GFP_KERNEL, 1);
> >> + if (!dst) {
> >> + pr_err("zswap: can't allocate compressor buffer\n");
> >> + crypto_free_comp(tfm);
> >> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> >> + return NOTIFY_BAD;
> >> + }
> >> + per_cpu(zswap_dstmem, cpu) = dst;
> >> + break;
> >> + case CPU_DEAD:
> >> + case CPU_UP_CANCELED:
> >> + tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
> >> + if (tfm) {
> >> + crypto_free_comp(tfm);
> >> + *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
> >> + }
> >> + dst = per_cpu(zswap_dstmem, cpu);
> >> + if (dst) {
> >> + free_pages((unsigned long)dst, 1);
> >> + per_cpu(zswap_dstmem, cpu) = NULL;
> >> + }
> >> + break;
> >> + default:
> >> + break;
> >> + }
> >> + return NOTIFY_OK;
> >> +}
> >> +
> >> +static int zswap_cpu_notifier(struct notifier_block *nb,
> >> + unsigned long action, void *pcpu)
> >> +{
> >> + unsigned long cpu = (unsigned long)pcpu;
> >> + return __zswap_cpu_notifier(action, cpu);
> >> +}
> >> +
> >> +static struct notifier_block zswap_cpu_notifier_block = {
> >> + .notifier_call = zswap_cpu_notifier
> >> +};
> >> +
> >> +static int zswap_cpu_init(void)
> >> +{
> >> + unsigned long cpu;
> >> +
> >> + get_online_cpus();
> >> + for_each_online_cpu(cpu)
> >> + if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
> >> + goto cleanup;
> >> + register_cpu_notifier(&zswap_cpu_notifier_block);
> >> + put_online_cpus();
> >> + return 0;
> >> +
> >> +cleanup:
> >> + for_each_online_cpu(cpu)
> >> + __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
> >> + put_online_cpus();
> >> + return -ENOMEM;
> >> +}
> >> +
> >> +/*********************************
> >> +* zsmalloc callbacks
> >> +**********************************/
> >> +static mempool_t *zswap_page_pool;
> >> +
> >> +static u64 zswap_pool_limit_hit;
> >> +
> >> +static inline unsigned int zswap_max_pool_pages(void)
> >> +{
> >> + return zswap_max_pool_percent * totalram_pages / 100;
> >> +}
> >> +
> >> +static inline int zswap_page_pool_create(void)
> >> +{
> >> + zswap_page_pool = mempool_create_page_pool(256, 0);
> >
> > Could you write down why you select pool to 256?
> > If you have a plan, please write down it as TODO.
> > I think it could be a function of zswap_max_pool_pages with min/max.
>
> Yes, that would probably be better.
>
> >
> > Another question.
> >
> > What's the benefit of using mempool for zsmalloc?
> > As you know, zsmalloc doesn't use mempool as default.
> > I guess you see some benefit. if so, zram could be changed.
> > If we can change zsmalloc's default scheme to use mempool,
> > all of customer of zsmalloc could be enhanced, too.
>
> In the case of zswap, through experimentation, I found that adding a
> mempool behind the zsmalloc pool added some elasticity to the pool.
> Fewer stores failed if we kept a small reserve of pages around instead
> of having to go back to the buddy allocator who, under memory
> pressure, is more likely to reject our request.
>
> I don't see this situation being applicable to all zsmalloc users
> however. I don't think we want incorporate it directly into zsmalloc
> for now. The ability to register custom page alloc/free functions at
> pool creation time allows users to do something special, like back
> with a mempool, if they want to do that.
Okay. I'd like to test this approach with zram later and if it makes sense
for everything, I will try to change zsmalloc's inside.
Thanks!
--
Kind regards,
Minchan Kim
--
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^ permalink raw reply [flat|nested] 38+ messages in thread
* RE: [PATCHv3 5/6] zswap: add to mm/
2013-01-29 17:26 ` Seth Jennings
@ 2013-02-06 23:47 ` Dan Magenheimer
-1 siblings, 0 replies; 38+ messages in thread
From: Dan Magenheimer @ 2013-02-06 23:47 UTC (permalink / raw)
To: Seth Jennings, Minchan Kim
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Konrad Wilk,
Robert Jennings, Jenifer Hopper, Mel Gorman, Johannes Weiner,
Rik van Riel, Larry Woodman, Benjamin Herrenschmidt, Dave Hansen,
linux-mm, linux-kernel, devel
> From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com]
> Subject: Re: [PATCHv3 5/6] zswap: add to mm/
>
> On 01/29/2013 12:27 AM, Minchan Kim wrote:
> > First feeling is it's simple and nice approach.
> > Although we have some problems to decide policy, it could solve by later patch
> > so I hope we make basic infrasture more solid by lots of comment.
>
> Thanks very much for the review!
> >
> > Another question.
> >
> > What's the benefit of using mempool for zsmalloc?
> > As you know, zsmalloc doesn't use mempool as default.
> > I guess you see some benefit. if so, zram could be changed.
> > If we can change zsmalloc's default scheme to use mempool,
> > all of customer of zsmalloc could be enhanced, too.
>
> In the case of zswap, through experimentation, I found that adding a
> mempool behind the zsmalloc pool added some elasticity to the pool.
> Fewer stores failed if we kept a small reserve of pages around instead
> of having to go back to the buddy allocator who, under memory
> pressure, is more likely to reject our request.
>
> I don't see this situation being applicable to all zsmalloc users
> however. I don't think we want incorporate it directly into zsmalloc
> for now. The ability to register custom page alloc/free functions at
> pool creation time allows users to do something special, like back
> with a mempool, if they want to do that.
(sorry, still catching up on backlog after being gone last week)
IIUC, by using mempool, you are essentially setting aside a
special cache of pageframes that only zswap can use (or other
users of mempool, I don't know what other subsystems use it).
So one would expect that fewer stores would fail if more
pageframes are available to zswap, the same as if you had
increased zswap_max_pool_percent by some small fraction.
But by setting those pageframes aside, you are keeping them from
general use, which may be a use with a higher priority as determined
by the mm system.
This seems wrong to me. Should every subsystem hide a bunch of
pageframes away in case it might need them?
Or am I missing something?
Dan
^ permalink raw reply [flat|nested] 38+ messages in thread
* RE: [PATCHv3 5/6] zswap: add to mm/
@ 2013-02-06 23:47 ` Dan Magenheimer
0 siblings, 0 replies; 38+ messages in thread
From: Dan Magenheimer @ 2013-02-06 23:47 UTC (permalink / raw)
To: Seth Jennings, Minchan Kim
Cc: Andrew Morton, Greg Kroah-Hartman, Nitin Gupta, Konrad Wilk,
Robert Jennings, Jenifer Hopper, Mel Gorman, Johannes Weiner,
Rik van Riel, Larry Woodman, Benjamin Herrenschmidt, Dave Hansen,
linux-mm, linux-kernel, devel
> From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com]
> Subject: Re: [PATCHv3 5/6] zswap: add to mm/
>
> On 01/29/2013 12:27 AM, Minchan Kim wrote:
> > First feeling is it's simple and nice approach.
> > Although we have some problems to decide policy, it could solve by later patch
> > so I hope we make basic infrasture more solid by lots of comment.
>
> Thanks very much for the review!
> >
> > Another question.
> >
> > What's the benefit of using mempool for zsmalloc?
> > As you know, zsmalloc doesn't use mempool as default.
> > I guess you see some benefit. if so, zram could be changed.
> > If we can change zsmalloc's default scheme to use mempool,
> > all of customer of zsmalloc could be enhanced, too.
>
> In the case of zswap, through experimentation, I found that adding a
> mempool behind the zsmalloc pool added some elasticity to the pool.
> Fewer stores failed if we kept a small reserve of pages around instead
> of having to go back to the buddy allocator who, under memory
> pressure, is more likely to reject our request.
>
> I don't see this situation being applicable to all zsmalloc users
> however. I don't think we want incorporate it directly into zsmalloc
> for now. The ability to register custom page alloc/free functions at
> pool creation time allows users to do something special, like back
> with a mempool, if they want to do that.
(sorry, still catching up on backlog after being gone last week)
IIUC, by using mempool, you are essentially setting aside a
special cache of pageframes that only zswap can use (or other
users of mempool, I don't know what other subsystems use it).
So one would expect that fewer stores would fail if more
pageframes are available to zswap, the same as if you had
increased zswap_max_pool_percent by some small fraction.
But by setting those pageframes aside, you are keeping them from
general use, which may be a use with a higher priority as determined
by the mm system.
This seems wrong to me. Should every subsystem hide a bunch of
pageframes away in case it might need them?
Or am I missing something?
Dan
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^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
2013-02-06 23:47 ` Dan Magenheimer
@ 2013-02-07 3:08 ` Seth Jennings
-1 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-02-07 3:08 UTC (permalink / raw)
To: Dan Magenheimer
Cc: Minchan Kim, Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Wilk, Robert Jennings, Jenifer Hopper, Mel Gorman,
Johannes Weiner, Rik van Riel, Larry Woodman,
Benjamin Herrenschmidt, Dave Hansen, linux-mm, linux-kernel,
devel
On 02/06/2013 05:47 PM, Dan Magenheimer wrote:
>> From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com]
>> Subject: Re: [PATCHv3 5/6] zswap: add to mm/
>>
>> On 01/29/2013 12:27 AM, Minchan Kim wrote:
>>> First feeling is it's simple and nice approach.
>>> Although we have some problems to decide policy, it could solve by later patch
>>> so I hope we make basic infrasture more solid by lots of comment.
>>
>> Thanks very much for the review!
>>>
>>> Another question.
>>>
>>> What's the benefit of using mempool for zsmalloc?
>>> As you know, zsmalloc doesn't use mempool as default.
>>> I guess you see some benefit. if so, zram could be changed.
>>> If we can change zsmalloc's default scheme to use mempool,
>>> all of customer of zsmalloc could be enhanced, too.
>>
>> In the case of zswap, through experimentation, I found that adding a
>> mempool behind the zsmalloc pool added some elasticity to the pool.
>> Fewer stores failed if we kept a small reserve of pages around instead
>> of having to go back to the buddy allocator who, under memory
>> pressure, is more likely to reject our request.
>>
>> I don't see this situation being applicable to all zsmalloc users
>> however. I don't think we want incorporate it directly into zsmalloc
>> for now. The ability to register custom page alloc/free functions at
>> pool creation time allows users to do something special, like back
>> with a mempool, if they want to do that.
>
> (sorry, still catching up on backlog after being gone last week)
>
> IIUC, by using mempool, you are essentially setting aside a
> special cache of pageframes that only zswap can use (or other
> users of mempool, I don't know what other subsystems use it).
> So one would expect that fewer stores would fail if more
> pageframes are available to zswap, the same as if you had
> increased zswap_max_pool_percent by some small fraction.
Yes this is correct.
>
> But by setting those pageframes aside, you are keeping them from
> general use, which may be a use with a higher priority as determined
> by the mm system.
>
> This seems wrong to me. Should every subsystem hide a bunch of
> pageframes away in case it might need them?
Well, like you said, any user of mempool does this. There were two
reasons for using it in this way in zswap:
(1) pages allocations and frees happen very frequently and going to
the buddy allocator every time for these operations is more expensive.
Especially the free-then-alloc pattern. Its faster to free to a
mempool (if it is below its minimum) then get that page right back,
than free to the buddy allocator and (try to) get that page back.
(2) the bursty nature of swap writeback leads to a large number of
failures if there isn't some pool of pages ready to accept them,
especially for workloads with bursty memory demands. The workload
suddenly requests a lot of memory, the system starts swapping, zswap
asks for pages but the buddy allocator is already swamped by requests
from the workload which isn't yet being throttled by direct reclaim.
The zswap allocations all fail and pages race by into the swap device.
Having a mempool allows for a little buffer. By the time the buffer
is used up, hopefully the workload is being throttled and the system
is more balanced.
Thanks,
Seth
^ permalink raw reply [flat|nested] 38+ messages in thread
* Re: [PATCHv3 5/6] zswap: add to mm/
@ 2013-02-07 3:08 ` Seth Jennings
0 siblings, 0 replies; 38+ messages in thread
From: Seth Jennings @ 2013-02-07 3:08 UTC (permalink / raw)
To: Dan Magenheimer
Cc: Minchan Kim, Andrew Morton, Greg Kroah-Hartman, Nitin Gupta,
Konrad Wilk, Robert Jennings, Jenifer Hopper, Mel Gorman,
Johannes Weiner, Rik van Riel, Larry Woodman,
Benjamin Herrenschmidt, Dave Hansen, linux-mm, linux-kernel,
devel
On 02/06/2013 05:47 PM, Dan Magenheimer wrote:
>> From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com]
>> Subject: Re: [PATCHv3 5/6] zswap: add to mm/
>>
>> On 01/29/2013 12:27 AM, Minchan Kim wrote:
>>> First feeling is it's simple and nice approach.
>>> Although we have some problems to decide policy, it could solve by later patch
>>> so I hope we make basic infrasture more solid by lots of comment.
>>
>> Thanks very much for the review!
>>>
>>> Another question.
>>>
>>> What's the benefit of using mempool for zsmalloc?
>>> As you know, zsmalloc doesn't use mempool as default.
>>> I guess you see some benefit. if so, zram could be changed.
>>> If we can change zsmalloc's default scheme to use mempool,
>>> all of customer of zsmalloc could be enhanced, too.
>>
>> In the case of zswap, through experimentation, I found that adding a
>> mempool behind the zsmalloc pool added some elasticity to the pool.
>> Fewer stores failed if we kept a small reserve of pages around instead
>> of having to go back to the buddy allocator who, under memory
>> pressure, is more likely to reject our request.
>>
>> I don't see this situation being applicable to all zsmalloc users
>> however. I don't think we want incorporate it directly into zsmalloc
>> for now. The ability to register custom page alloc/free functions at
>> pool creation time allows users to do something special, like back
>> with a mempool, if they want to do that.
>
> (sorry, still catching up on backlog after being gone last week)
>
> IIUC, by using mempool, you are essentially setting aside a
> special cache of pageframes that only zswap can use (or other
> users of mempool, I don't know what other subsystems use it).
> So one would expect that fewer stores would fail if more
> pageframes are available to zswap, the same as if you had
> increased zswap_max_pool_percent by some small fraction.
Yes this is correct.
>
> But by setting those pageframes aside, you are keeping them from
> general use, which may be a use with a higher priority as determined
> by the mm system.
>
> This seems wrong to me. Should every subsystem hide a bunch of
> pageframes away in case it might need them?
Well, like you said, any user of mempool does this. There were two
reasons for using it in this way in zswap:
(1) pages allocations and frees happen very frequently and going to
the buddy allocator every time for these operations is more expensive.
Especially the free-then-alloc pattern. Its faster to free to a
mempool (if it is below its minimum) then get that page right back,
than free to the buddy allocator and (try to) get that page back.
(2) the bursty nature of swap writeback leads to a large number of
failures if there isn't some pool of pages ready to accept them,
especially for workloads with bursty memory demands. The workload
suddenly requests a lot of memory, the system starts swapping, zswap
asks for pages but the buddy allocator is already swamped by requests
from the workload which isn't yet being throttled by direct reclaim.
The zswap allocations all fail and pages race by into the swap device.
Having a mempool allows for a little buffer. By the time the buffer
is used up, hopefully the workload is being throttled and the system
is more balanced.
Thanks,
Seth
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
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^ permalink raw reply [flat|nested] 38+ messages in thread
end of thread, other threads:[~2013-02-07 3:08 UTC | newest]
Thread overview: 38+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-01-28 21:49 [PATCHv3 0/6] zswap: compressed swap caching Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-28 21:49 ` [PATCHv3 1/6] debugfs: add get/set for atomic types Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-29 20:35 ` Konrad Rzeszutek Wilk
2013-01-29 20:35 ` Konrad Rzeszutek Wilk
2013-01-29 20:49 ` Seth Jennings
2013-01-29 20:49 ` Seth Jennings
2013-01-28 21:49 ` [PATCHv3 2/6] zsmalloc: promote to lib/ Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-28 23:56 ` Minchan Kim
2013-01-28 23:56 ` Minchan Kim
2013-01-28 21:49 ` [PATCHv3 3/6] mm: break up swap_writepage() for frontswap backends Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-28 23:58 ` Minchan Kim
2013-01-28 23:58 ` Minchan Kim
2013-01-28 21:49 ` [PATCHv3 4/6] mm: allow for outstanding swap writeback accounting Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-29 0:01 ` Minchan Kim
2013-01-29 0:01 ` Minchan Kim
2013-01-28 21:49 ` [PATCHv3 5/6] zswap: add to mm/ Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-29 6:27 ` Minchan Kim
2013-01-29 6:27 ` Minchan Kim
2013-01-29 17:26 ` Seth Jennings
2013-01-29 17:26 ` Seth Jennings
2013-01-30 4:44 ` Minchan Kim
2013-01-30 4:44 ` Minchan Kim
2013-02-06 23:47 ` Dan Magenheimer
2013-02-06 23:47 ` Dan Magenheimer
2013-02-07 3:08 ` Seth Jennings
2013-02-07 3:08 ` Seth Jennings
2013-01-29 18:55 ` Seth Jennings
2013-01-29 18:55 ` Seth Jennings
2013-01-28 21:49 ` [PATCHv3 6/6] zswap: add documentation Seth Jennings
2013-01-28 21:49 ` Seth Jennings
2013-01-28 22:08 ` [PATCHv3 0/6] zswap: compressed swap caching Seth Jennings
2013-01-28 22:08 ` Seth Jennings
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