* [PATCH v14 1/5] xenbus/backend: Add memory pressure handler callback
2020-01-27 8:18 [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback sjpark
@ 2020-01-27 8:18 ` sjpark
2020-01-27 8:18 ` [PATCH v14 2/5] xenbus/backend: Protect xenbus callback with lock sjpark
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: sjpark @ 2020-01-27 8:18 UTC (permalink / raw)
To: jgross, roger.pau, axboe
Cc: SeongJae Park, konrad.wilk, pdurrant, xen-devel, linux-block,
linux-kernel
From: SeongJae Park <sjpark@amazon.de>
Granting pages consumes backend system memory. In systems configured
with insufficient spare memory for those pages, it can cause a memory
pressure situation. However, finding the optimal amount of the spare
memory is challenging for large systems having dynamic resource
utilization patterns. Also, such a static configuration might lack
flexibility.
To mitigate such problems, this commit adds a memory reclaim callback to
'xenbus_driver'. If a memory pressure is detected, 'xenbus' requests
every backend driver to volunarily release its memory.
Note that it would be able to improve the callback facility for more
sophisticated handlings of general pressures. For example, it would be
possible to monitor the memory consumption of each device and issue the
release requests to only devices which causing the pressure. Also, the
callback could be extended to handle not only memory, but general
resources. Nevertheless, this version of the implementation defers such
sophisticated goals as a future work.
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
drivers/xen/xenbus/xenbus_probe_backend.c | 32 +++++++++++++++++++++++
include/xen/xenbus.h | 1 +
2 files changed, 33 insertions(+)
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index 14876faff3b0..3b5cb7a5a7e4 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -247,6 +247,35 @@ static int backend_probe_and_watch(struct notifier_block *notifier,
return NOTIFY_DONE;
}
+static int backend_reclaim_memory(struct device *dev, void *data)
+{
+ const struct xenbus_driver *drv;
+
+ if (!dev->driver)
+ return 0;
+ drv = to_xenbus_driver(dev->driver);
+ if (drv && drv->reclaim_memory)
+ drv->reclaim_memory(to_xenbus_device(dev));
+ return 0;
+}
+
+/*
+ * Returns 0 always because we are using shrinker to only detect memory
+ * pressure.
+ */
+static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
+ backend_reclaim_memory);
+ return 0;
+}
+
+static struct shrinker backend_memory_shrinker = {
+ .count_objects = backend_shrink_memory_count,
+ .seeks = DEFAULT_SEEKS,
+};
+
static int __init xenbus_probe_backend_init(void)
{
static struct notifier_block xenstore_notifier = {
@@ -263,6 +292,9 @@ static int __init xenbus_probe_backend_init(void)
register_xenstore_notifier(&xenstore_notifier);
+ if (register_shrinker(&backend_memory_shrinker))
+ pr_warn("shrinker registration failed\n");
+
return 0;
}
subsys_initcall(xenbus_probe_backend_init);
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 24228a102141..980952ea452b 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -105,6 +105,7 @@ struct xenbus_driver {
struct device_driver driver;
int (*read_otherend_details)(struct xenbus_device *dev);
int (*is_ready)(struct xenbus_device *dev);
+ void (*reclaim_memory)(struct xenbus_device *dev);
};
static inline struct xenbus_driver *to_xenbus_driver(struct device_driver *drv)
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH v14 2/5] xenbus/backend: Protect xenbus callback with lock
2020-01-27 8:18 [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback sjpark
2020-01-27 8:18 ` [PATCH v14 1/5] " sjpark
@ 2020-01-27 8:18 ` sjpark
2020-01-27 8:18 ` [PATCH v14 3/5] xen/blkback: Squeeze page pools if a memory pressure is detected sjpark
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: sjpark @ 2020-01-27 8:18 UTC (permalink / raw)
To: jgross, roger.pau, axboe
Cc: SeongJae Park, konrad.wilk, pdurrant, xen-devel, linux-block,
linux-kernel
From: SeongJae Park <sjpark@amazon.de>
A driver's 'reclaim_memory' callback can race with 'probe' or 'remove'
because it will be called whenever memory pressure is detected. To
avoid such race, this commit embeds a spinlock in each 'xenbus_device'
and make 'xenbus' to hold the lock while the corresponded callbacks are
running.
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
drivers/xen/xenbus/xenbus_probe.c | 8 +++++++-
drivers/xen/xenbus/xenbus_probe_backend.c | 10 ++++++++--
include/xen/xenbus.h | 1 +
3 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 378486b79f96..66975da4f3b6 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -239,7 +239,9 @@ int xenbus_dev_probe(struct device *_dev)
goto fail;
}
+ spin_lock(&dev->reclaim_lock);
err = drv->probe(dev, id);
+ spin_unlock(&dev->reclaim_lock);
if (err)
goto fail_put;
@@ -268,8 +270,11 @@ int xenbus_dev_remove(struct device *_dev)
free_otherend_watch(dev);
- if (drv->remove)
+ if (drv->remove) {
+ spin_lock(&dev->reclaim_lock);
drv->remove(dev);
+ spin_unlock(&dev->reclaim_lock);
+ }
module_put(drv->driver.owner);
@@ -468,6 +473,7 @@ int xenbus_probe_node(struct xen_bus_type *bus,
goto fail;
dev_set_name(&xendev->dev, "%s", devname);
+ spin_lock_init(&xendev->reclaim_lock);
/* Register with generic device framework. */
err = device_register(&xendev->dev);
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index 3b5cb7a5a7e4..791f6fe01e91 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -250,12 +250,18 @@ static int backend_probe_and_watch(struct notifier_block *notifier,
static int backend_reclaim_memory(struct device *dev, void *data)
{
const struct xenbus_driver *drv;
+ struct xenbus_device *xdev;
if (!dev->driver)
return 0;
drv = to_xenbus_driver(dev->driver);
- if (drv && drv->reclaim_memory)
- drv->reclaim_memory(to_xenbus_device(dev));
+ if (drv && drv->reclaim_memory) {
+ xdev = to_xenbus_device(dev);
+ if (!spin_trylock(&xdev->reclaim_lock))
+ return 0;
+ drv->reclaim_memory(xdev);
+ spin_unlock(&xdev->reclaim_lock);
+ }
return 0;
}
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 980952ea452b..89a889585ba0 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -76,6 +76,7 @@ struct xenbus_device {
enum xenbus_state state;
struct completion down;
struct work_struct work;
+ spinlock_t reclaim_lock;
};
static inline struct xenbus_device *to_xenbus_device(struct device *dev)
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH v14 3/5] xen/blkback: Squeeze page pools if a memory pressure is detected
2020-01-27 8:18 [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback sjpark
2020-01-27 8:18 ` [PATCH v14 1/5] " sjpark
2020-01-27 8:18 ` [PATCH v14 2/5] xenbus/backend: Protect xenbus callback with lock sjpark
@ 2020-01-27 8:18 ` sjpark
2020-01-27 8:18 ` [PATCH v14 4/5] xen/blkback: Remove unnecessary static variable name prefixes sjpark
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: sjpark @ 2020-01-27 8:18 UTC (permalink / raw)
To: jgross, roger.pau, axboe
Cc: SeongJae Park, konrad.wilk, pdurrant, xen-devel, linux-block,
linux-kernel
From: SeongJae Park <sjpark@amazon.de>
Each `blkif` has a free pages pool for the grant mapping. The size of
the pool starts from zero and is increased on demand while processing
the I/O requests. If current I/O requests handling is finished or 100
milliseconds has passed since last I/O requests handling, it checks and
shrinks the pool to not exceed the size limit, `max_buffer_pages`.
Therefore, host administrators can cause memory pressure in blkback by
attaching a large number of block devices and inducing I/O. Such
problematic situations can be avoided by limiting the maximum number of
devices that can be attached, but finding the optimal limit is not so
easy. Improper set of the limit can results in memory pressure or a
resource underutilization. This commit avoids such problematic
situations by squeezing the pools (returns every free page in the pool
to the system) for a while (users can set this duration via a module
parameter) if memory pressure is detected.
Discussions
===========
The `blkback`'s original shrinking mechanism returns only pages in the
pool which are not currently be used by `blkback` to the system. In
other words, the pages that are not mapped with granted pages. Because
this commit is changing only the shrink limit but still uses the same
freeing mechanism it does not touch pages which are currently mapping
grants.
Once memory pressure is detected, this commit keeps the squeezing limit
for a user-specified time duration. The duration should be neither too
long nor too short. If it is too long, the squeezing incurring overhead
can reduce the I/O performance. If it is too short, `blkback` will not
free enough pages to reduce the memory pressure. This commit sets the
value as `10 milliseconds` by default because it is a short time in
terms of I/O while it is a long time in terms of memory operations.
Also, as the original shrinking mechanism works for at least every 100
milliseconds, this could be a somewhat reasonable choice. I also tested
other durations (refer to the below section for more details) and
confirmed that 10 milliseconds is the one that works best with the test.
That said, the proper duration depends on actual configurations and
workloads. That's why this commit allows users to set the duration as a
module parameter.
Memory Pressure Test
====================
To show how this commit fixes the memory pressure situation well, I
configured a test environment on a xen-running virtualization system.
On the `blkfront` running guest instances, I attach a large number of
network-backed volume devices and induce I/O to those. Meanwhile, I
measure the number of pages that swapped in (pswpin) and out (pswpout)
on the `blkback` running guest. The test ran twice, once for the
`blkback` before this commit and once for that after this commit. As
shown below, this commit has dramatically reduced the memory pressure:
pswpin pswpout
before 76,672 185,799
after 867 3,967
Optimal Aggressive Shrinking Duration
-------------------------------------
To find a best squeezing duration, I repeated the test with three
different durations (1ms, 10ms, and 100ms). The results are as below:
duration pswpin pswpout
1 707 5,095
10 867 3,967
100 362 3,348
As expected, the memory pressure decreases as the duration increases,
but the reduction become slow from the `10ms`. Based on this results, I
chose the default duration as 10ms.
Performance Overhead Test
=========================
This commit could incur I/O performance degradation under severe memory
pressure because the squeezing will require more page allocations per
I/O. To show the overhead, I artificially made a worst-case squeezing
situation and measured the I/O performance of a `blkfront` running
guest.
For the artificial squeezing, I set the `blkback.max_buffer_pages` using
the `/sys/module/xen_blkback/parameters/max_buffer_pages` file. In this
test, I set the value to `1024` and `0`. The `1024` is the default
value. Setting the value as `0` is same to a situation doing the
squeezing always (worst-case).
If the underlying block device is slow enough, the squeezing overhead
could be hidden. For the reason, I use a fast block device, namely the
rbd[1]:
# xl block-attach guest phy:/dev/ram0 xvdb w
For the I/O performance measurement, I run a simple `dd` command 5 times
directly to the device as below and collect the 'MB/s' results.
$ for i in {1..5}; do dd if=/dev/zero of=/dev/xvdb \
bs=4k count=$((256*512)); sync; done
The results are as below. 'max_pgs' represents the value of the
`blkback.max_buffer_pages` parameter.
max_pgs Min Max Median Avg Stddev
0 417 423 420 419.4 2.5099801
1024 414 425 416 417.8 4.4384682
No difference proven at 95.0% confidence
In short, even worst case squeezing on ramdisk based fast block device
makes no visible performance degradation. Please note that this is just
a very simple and minimal test. On systems using super-fast block
devices and a special I/O workload, the results might be different. If
you have any doubt, test on your machine with your workload to find the
optimal squeezing duration for you.
[1] https://www.kernel.org/doc/html/latest/admin-guide/blockdev/ramdisk.html
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
.../ABI/testing/sysfs-driver-xen-blkback | 10 +++++++++
drivers/block/xen-blkback/blkback.c | 7 +++++--
drivers/block/xen-blkback/common.h | 1 +
drivers/block/xen-blkback/xenbus.c | 21 +++++++++++++++++++
4 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
index 4e7babb3ba1f..ecb7942ff146 100644
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
@@ -25,3 +25,13 @@ Description:
allocated without being in use. The time is in
seconds, 0 means indefinitely long.
The default is 60 seconds.
+
+What: /sys/module/xen_blkback/parameters/buffer_squeeze_duration_ms
+Date: December 2019
+KernelVersion: 5.6
+Contact: SeongJae Park <sjpark@amazon.de>
+Description:
+ When memory pressure is reported to blkback this option
+ controls the duration in milliseconds that blkback will not
+ cache any page not backed by a grant mapping.
+ The default is 10ms.
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 716b99aa2307..5b9ee0494e15 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -656,8 +656,11 @@ int xen_blkif_schedule(void *arg)
ring->next_lru = jiffies + msecs_to_jiffies(LRU_INTERVAL);
}
- /* Shrink if we have more than xen_blkif_max_buffer_pages */
- shrink_free_pagepool(ring, xen_blkif_max_buffer_pages);
+ /* Shrink the free pages pool if it is too large. */
+ if (time_before(jiffies, blkif->buffer_squeeze_end))
+ shrink_free_pagepool(ring, 0);
+ else
+ shrink_free_pagepool(ring, xen_blkif_max_buffer_pages);
if (log_stats && time_after(jiffies, ring->st_print))
print_stats(ring);
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index 49132b0adbbe..a3eeccf3ac5f 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -319,6 +319,7 @@ struct xen_blkif {
/* All rings for this device. */
struct xen_blkif_ring *rings;
unsigned int nr_rings;
+ unsigned long buffer_squeeze_end;
};
struct seg_buf {
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 4c5d99f87813..55960190b774 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -859,6 +859,26 @@ static void frontend_changed(struct xenbus_device *dev,
}
+/* Once a memory pressure is detected, squeeze free page pools for a while. */
+static unsigned int buffer_squeeze_duration_ms = 10;
+module_param_named(buffer_squeeze_duration_ms,
+ buffer_squeeze_duration_ms, int, 0644);
+MODULE_PARM_DESC(buffer_squeeze_duration_ms,
+"Duration in ms to squeeze pages buffer when a memory pressure is detected");
+
+/*
+ * Callback received when the memory pressure is detected.
+ */
+static void reclaim_memory(struct xenbus_device *dev)
+{
+ struct backend_info *be = dev_get_drvdata(&dev->dev);
+
+ if (!be)
+ return;
+ be->blkif->buffer_squeeze_end = jiffies +
+ msecs_to_jiffies(buffer_squeeze_duration_ms);
+}
+
/* ** Connection ** */
@@ -1152,6 +1172,7 @@ static struct xenbus_driver xen_blkbk_driver = {
.remove = xen_blkbk_remove,
.otherend_changed = frontend_changed,
.allow_rebind = true,
+ .reclaim_memory = reclaim_memory,
};
int xen_blkif_xenbus_init(void)
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH v14 4/5] xen/blkback: Remove unnecessary static variable name prefixes
2020-01-27 8:18 [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback sjpark
` (2 preceding siblings ...)
2020-01-27 8:18 ` [PATCH v14 3/5] xen/blkback: Squeeze page pools if a memory pressure is detected sjpark
@ 2020-01-27 8:18 ` sjpark
2020-01-27 8:19 ` [PATCH v14 5/5] xen/blkback: Consistently insert one empty line between functions sjpark
2020-01-30 13:21 ` [Xen-devel] [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback Boris Ostrovsky
5 siblings, 0 replies; 7+ messages in thread
From: sjpark @ 2020-01-27 8:18 UTC (permalink / raw)
To: jgross, roger.pau, axboe
Cc: SeongJae Park, konrad.wilk, pdurrant, xen-devel, linux-block,
linux-kernel
From: SeongJae Park <sjpark@amazon.de>
A few of static variables in blkback have 'xen_blkif_' prefix, though it
is unnecessary for static variables. This commit removes such prefixes.
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
drivers/block/xen-blkback/blkback.c | 37 +++++++++++++----------------
1 file changed, 17 insertions(+), 20 deletions(-)
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 5b9ee0494e15..c2f71265af4b 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -62,8 +62,8 @@
* IO workloads.
*/
-static int xen_blkif_max_buffer_pages = 1024;
-module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644);
+static int max_buffer_pages = 1024;
+module_param_named(max_buffer_pages, max_buffer_pages, int, 0644);
MODULE_PARM_DESC(max_buffer_pages,
"Maximum number of free pages to keep in each block backend buffer");
@@ -78,8 +78,8 @@ MODULE_PARM_DESC(max_buffer_pages,
* algorithm.
*/
-static int xen_blkif_max_pgrants = 1056;
-module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
+static int max_pgrants = 1056;
+module_param_named(max_persistent_grants, max_pgrants, int, 0644);
MODULE_PARM_DESC(max_persistent_grants,
"Maximum number of grants to map persistently");
@@ -88,8 +88,8 @@ MODULE_PARM_DESC(max_persistent_grants,
* use. The time is in seconds, 0 means indefinitely long.
*/
-static unsigned int xen_blkif_pgrant_timeout = 60;
-module_param_named(persistent_grant_unused_seconds, xen_blkif_pgrant_timeout,
+static unsigned int pgrant_timeout = 60;
+module_param_named(persistent_grant_unused_seconds, pgrant_timeout,
uint, 0644);
MODULE_PARM_DESC(persistent_grant_unused_seconds,
"Time in seconds an unused persistent grant is allowed to "
@@ -137,9 +137,8 @@ module_param(log_stats, int, 0644);
static inline bool persistent_gnt_timeout(struct persistent_gnt *persistent_gnt)
{
- return xen_blkif_pgrant_timeout &&
- (jiffies - persistent_gnt->last_used >=
- HZ * xen_blkif_pgrant_timeout);
+ return pgrant_timeout && (jiffies - persistent_gnt->last_used >=
+ HZ * pgrant_timeout);
}
static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page)
@@ -234,7 +233,7 @@ static int add_persistent_gnt(struct xen_blkif_ring *ring,
struct persistent_gnt *this;
struct xen_blkif *blkif = ring->blkif;
- if (ring->persistent_gnt_c >= xen_blkif_max_pgrants) {
+ if (ring->persistent_gnt_c >= max_pgrants) {
if (!blkif->vbd.overflow_max_grants)
blkif->vbd.overflow_max_grants = 1;
return -EBUSY;
@@ -397,14 +396,13 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring)
goto out;
}
- if (ring->persistent_gnt_c < xen_blkif_max_pgrants ||
- (ring->persistent_gnt_c == xen_blkif_max_pgrants &&
+ if (ring->persistent_gnt_c < max_pgrants ||
+ (ring->persistent_gnt_c == max_pgrants &&
!ring->blkif->vbd.overflow_max_grants)) {
num_clean = 0;
} else {
- num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
- num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants +
- num_clean;
+ num_clean = (max_pgrants / 100) * LRU_PERCENT_CLEAN;
+ num_clean = ring->persistent_gnt_c - max_pgrants + num_clean;
num_clean = min(ring->persistent_gnt_c, num_clean);
pr_debug("Going to purge at least %u persistent grants\n",
num_clean);
@@ -599,8 +597,7 @@ static void print_stats(struct xen_blkif_ring *ring)
current->comm, ring->st_oo_req,
ring->st_rd_req, ring->st_wr_req,
ring->st_f_req, ring->st_ds_req,
- ring->persistent_gnt_c,
- xen_blkif_max_pgrants);
+ ring->persistent_gnt_c, max_pgrants);
ring->st_print = jiffies + msecs_to_jiffies(10 * 1000);
ring->st_rd_req = 0;
ring->st_wr_req = 0;
@@ -660,7 +657,7 @@ int xen_blkif_schedule(void *arg)
if (time_before(jiffies, blkif->buffer_squeeze_end))
shrink_free_pagepool(ring, 0);
else
- shrink_free_pagepool(ring, xen_blkif_max_buffer_pages);
+ shrink_free_pagepool(ring, max_buffer_pages);
if (log_stats && time_after(jiffies, ring->st_print))
print_stats(ring);
@@ -887,7 +884,7 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
continue;
}
if (use_persistent_gnts &&
- ring->persistent_gnt_c < xen_blkif_max_pgrants) {
+ ring->persistent_gnt_c < max_pgrants) {
/*
* We are using persistent grants, the grant is
* not mapped but we might have room for it.
@@ -914,7 +911,7 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring,
pages[seg_idx]->persistent_gnt = persistent_gnt;
pr_debug("grant %u added to the tree of persistent grants, using %u/%u\n",
persistent_gnt->gnt, ring->persistent_gnt_c,
- xen_blkif_max_pgrants);
+ max_pgrants);
goto next;
}
if (use_persistent_gnts && !blkif->vbd.overflow_max_grants) {
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH v14 5/5] xen/blkback: Consistently insert one empty line between functions
2020-01-27 8:18 [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback sjpark
` (3 preceding siblings ...)
2020-01-27 8:18 ` [PATCH v14 4/5] xen/blkback: Remove unnecessary static variable name prefixes sjpark
@ 2020-01-27 8:19 ` sjpark
2020-01-30 13:21 ` [Xen-devel] [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback Boris Ostrovsky
5 siblings, 0 replies; 7+ messages in thread
From: sjpark @ 2020-01-27 8:19 UTC (permalink / raw)
To: jgross, roger.pau, axboe
Cc: SeongJae Park, konrad.wilk, pdurrant, xen-devel, linux-block,
linux-kernel
From: SeongJae Park <sjpark@amazon.de>
The number of empty lines between functions in the xenbus.c is
inconsistent. This trivial style cleanup commit fixes the file to
consistently place only one empty line.
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
---
drivers/block/xen-blkback/xenbus.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 55960190b774..42944d41aea0 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -467,7 +467,6 @@ static void xenvbd_sysfs_delif(struct xenbus_device *dev)
device_remove_file(&dev->dev, &dev_attr_physical_device);
}
-
static void xen_vbd_free(struct xen_vbd *vbd)
{
if (vbd->bdev)
@@ -524,6 +523,7 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
handle, blkif->domid);
return 0;
}
+
static int xen_blkbk_remove(struct xenbus_device *dev)
{
struct backend_info *be = dev_get_drvdata(&dev->dev);
@@ -607,6 +607,7 @@ static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info
if (err)
dev_warn(&dev->dev, "writing feature-discard (%d)", err);
}
+
int xen_blkbk_barrier(struct xenbus_transaction xbt,
struct backend_info *be, int state)
{
@@ -691,7 +692,6 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
return err;
}
-
/*
* Callback received when the hotplug scripts have placed the physical-device
* node. Read it and the mode node, and create a vbd. If the frontend is
@@ -783,7 +783,6 @@ static void backend_changed(struct xenbus_watch *watch,
}
}
-
/*
* Callback received when the frontend's state changes.
*/
@@ -858,7 +857,6 @@ static void frontend_changed(struct xenbus_device *dev,
}
}
-
/* Once a memory pressure is detected, squeeze free page pools for a while. */
static unsigned int buffer_squeeze_duration_ms = 10;
module_param_named(buffer_squeeze_duration_ms,
@@ -881,7 +879,6 @@ static void reclaim_memory(struct xenbus_device *dev)
/* ** Connection ** */
-
/*
* Write the physical details regarding the block device to the store, and
* switch to Connected state.
--
2.17.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* Re: [Xen-devel] [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback
2020-01-27 8:18 [PATCH v14 0/5] xenbus/backend: Add memory pressure handler callback sjpark
` (4 preceding siblings ...)
2020-01-27 8:19 ` [PATCH v14 5/5] xen/blkback: Consistently insert one empty line between functions sjpark
@ 2020-01-30 13:21 ` Boris Ostrovsky
5 siblings, 0 replies; 7+ messages in thread
From: Boris Ostrovsky @ 2020-01-30 13:21 UTC (permalink / raw)
To: sjpark, jgross, roger.pau, axboe
Cc: konrad.wilk, pdurrant, SeongJae Park, linux-kernel, linux-block,
xen-devel
On 1/27/20 3:18 AM, sjpark@amazon.com wrote:
> From: SeongJae Park <sjpark@amazon.de>
>
> Granting pages consumes backend system memory. In systems configured
> with insufficient spare memory for those pages, it can cause a memory
> pressure situation. However, finding the optimal amount of the spare
> memory is challenging for large systems having dynamic resource
> utilization patterns. Also, such a static configuration might lack
> flexibility.
>
> To mitigate such problems, this patchset adds a memory reclaim callback
> to 'xenbus_driver' (patch 1) and then introduce a lock for race
> condition avoidance (patch 2). After that, patch 3 applies the callback
> mechanism to mitigate the problem in 'xen-blkback'. The fourth and
> fifth patches are trivial cleanups; those fix nits we found during the
> development of this patchset.
>
> Note that this patch has only trivial changes from v13. Please refer to
> below patch history for the changes.
>
Applied to for-linus-5.6.
-boris
^ permalink raw reply [flat|nested] 7+ messages in thread