[PATCH 0/2] [RFC] Volatile ranges (v4)

[PATCH 0/2] [RFC] Volatile ranges (v4)

[John Stultz]

Ok. So here's another iteration of the fadvise volatile range code.

I realize this is still a way off from being ready, but I wanted to post
what I have to share with folks working on the various range/interval
management ideas as well as update folks who've provided feedback on the
volatile range code.

So just on the premise: Ideally, I want delayed reclaim based hole
punching.

Application has a possibly shared mmapped cache file, which it can mark
chunks of which volatile or nonvolatile as it uses it.  If the kernel
needs memory, it can zap any ranges that are currently marked volatile. 

Some examples would be rendering of images or web pages that are not
on-screen. This allows the application to volunteer memory for
reclaiming, and the kernel to grab it only when it needs. This differs
from some of the memory notification schemes, in that it allows the
kernel to immediately reclaim what it needs, rather then having to
request applications to give up memory (which may add further memory
load) until enough is free. However, unlike the notification scheme,
it does require applications to mark and unmark pages as volatile as
they use them.

Current use cases (ie: users of Android's ashmem) only use shmfs/tmpfs.
However, I don't see right off why it should be limited to shm. As long
as punching a hole in a file can be done w/ minimal memory overhead
this could be useful and have somewhat sane behavior. 

We could also only zap the page cache, not writing any dirty data out.
However, w/ non-shm files, discarding dirty data without hole punching
would obviously leave persistent files in a non-coherent state. This
may further re-inforce that the design should be shm only if we don't
do hole punching.

On the topic of hole punching, the kernel doesn't seem completely
unified in this as well. As I understand, there are two methods to do
hole punching: FALLOCATE_FL_PUNCH_HOLE vs MADV_REMOVE, and they don't
necessarily overlap in support. For the most part, it seems persistent
filesystems require FALLOCATE_FL_PUNCH, where as shmfs/tmpfs uses
MADV_REMOVE. But I may be misunderstanding the subtle difference here,
so if anyone wants to clarify this, it would be great.

One concern was that if the design is shm only, fadvise might not be
the right interface, as it should be generic. The
madvise(MADV_REMOVE,...) interface gives some precedence to shmfs/tmpfs
only calls, but I'd like to get some further feedback as to what folks
think of this. If we are shm/tmpfs only, I could rework this design to
use madvise instead of fadvise if folks would prefer.

Also, there's still the issue that lockdep doesn't like me calling
vmtruncate_range from the shrinker due to any allocations being done
while the i_mutex is taken could cause the shrinker to run and need the
i_mutex again.  I did try using invalidate_inode_pages2_range() but it
always returns EBUSY in this context, so I suspect I want something
else. I'm currently reading shmem_truncate_range() and zap_page_range()
to get a better idea of how to this might be best accomplished.

Regarding feedback suggesting dropping the LRU ranges, and instead
keeping the volatile/purged data in radix tags and to manage things at
writeout time. My concern there is having the LRU behavior on the
entire range from when it was marked volatile instead of the actual
last page access (you might have ranges that have frequent use areas
and non-frequent use).  Also sorting out how to evict the entire range
when one page is dropped might be funky.  However, I'll likely revisit
this soon, but for this iteration I didn't get to it.

I still also realize I have the issue of bloating the address_space
structure to handle, and I suspect if I continue w/ this approach
I'll use a separate hash table to store the range-tree roots in my
next revision.

Anyway, thanks for the continued advice and feedback!
-john

CC: Andrew Morton <akpm@linux-foundation.org>
CC: Android Kernel Team <kernel-team@android.com>
CC: Robert Love <rlove@google.com>
CC: Mel Gorman <mel@csn.ul.ie>
CC: Hugh Dickins <hughd@google.com>
CC: Dave Hansen <dave@linux.vnet.ibm.com>
CC: Rik van Riel <riel@redhat.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Neil Brown <neilb@suse.de>
CC: Andrea Righi <andrea@betterlinux.com>
CC: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

John Stultz (2):
  [RFC] Range tree implementation
  [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE flags

 fs/inode.c                |    4 +
 include/linux/fadvise.h   |    5 +
 include/linux/fs.h        |    2 +
 include/linux/rangetree.h |   53 ++++++++
 include/linux/volatile.h  |   14 ++
 lib/Makefile              |    2 +-
 lib/rangetree.c           |  105 +++++++++++++++
 mm/Makefile               |    2 +-
 mm/fadvise.c              |   16 ++-
 mm/volatile.c             |  313 +++++++++++++++++++++++++++++++++++++++++++++
 10 files changed, 513 insertions(+), 3 deletions(-)
 create mode 100644 include/linux/rangetree.h
 create mode 100644 include/linux/volatile.h
 create mode 100644 lib/rangetree.c
 create mode 100644 mm/volatile.c

-- 
1.7.3.2.146.gca209

[PATCH 1/2] [RFC] Range tree implementation

[John Stultz]

After Andrew suggested something like his mumbletree idea
to better store a list of ranges, I worked on a few different
approaches, and this is what I've finally managed to get working.

I suspect range-tree isn't a totally accurate name, but I
couldn't quite make out the difference between range trees
and interval trees, so I just picked one to call it. Do
let me know if you have a better name.

The idea of storing ranges in a tree is nice, but has a number
of complications. When adding a range, its possible that a
large range will consume and merge a number of smaller ranges.
When removing a range, its possible you may end up splitting an
existing range, causing one range to become two. This makes it
very difficult to provide generic list_head like behavior, as
the parent structures would need to be duplicated and removed,
and that has lots of memory ownership issues.

So, this is a much simplified and more list_head like
implementation. You can add a node to a tree, or remove a node
to a tree, but the generic implementation doesn't do the
merging or splitting for you. But it does provide helpers to
find overlapping and adjacent ranges.

Andrew also really wanted this range-tree implementation to be
resuable so we don't duplicate the file locking logic. I'm not
totally convinced that the requirements between the volatile
ranges and file locking are really equivelent, but this reduced
impelementation may make it possible.

Do let me know what you think or if you have other ideas for
better ways to do the same.

Changelog:
v2:
* Reworked code to use an rbtree instead of splaying

CC: Andrew Morton <akpm@linux-foundation.org>
CC: Android Kernel Team <kernel-team@android.com>
CC: Robert Love <rlove@google.com>
CC: Mel Gorman <mel@csn.ul.ie>
CC: Hugh Dickins <hughd@google.com>
CC: Dave Hansen <dave@linux.vnet.ibm.com>
CC: Rik van Riel <riel@redhat.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Neil Brown <neilb@suse.de>
CC: Andrea Righi <andrea@betterlinux.com>
CC: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 include/linux/rangetree.h |   53 +++++++++++++++++++++++
 lib/Makefile              |    2 +-
 lib/rangetree.c           |  105 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 159 insertions(+), 1 deletions(-)
 create mode 100644 include/linux/rangetree.h
 create mode 100644 lib/rangetree.c

diff --git a/include/linux/rangetree.h b/include/linux/rangetree.h
new file mode 100644
index 0000000..ca03821
--- /dev/null
+++ b/include/linux/rangetree.h
@@ -0,0 +1,53 @@
+#ifndef _LINUX_RANGETREE_H
+#define _LINUX_RANGETREE_H
+
+#include <linux/types.h>
+#include <linux/rbtree.h>
+
+struct range_tree_node {
+	struct rb_node rb;
+	u64 start;
+	u64 end;
+};
+
+struct range_tree_root {
+	struct rb_root head;
+};
+
+static inline void range_tree_init(struct range_tree_root *root)
+{
+	root->head = RB_ROOT;
+}
+
+static inline void range_tree_node_init(struct range_tree_node *node)
+{
+	rb_init_node(&node->rb);
+	node->start = 0;
+	node->end = 0;
+}
+
+static inline int range_tree_empty(struct range_tree_root *root)
+{
+	return RB_EMPTY_ROOT(&root->head);
+}
+
+static inline
+struct range_tree_node *range_tree_root_node(struct range_tree_root *root)
+{
+	struct range_tree_node *ret;
+	ret = container_of(root->head.rb_node, struct range_tree_node, rb);
+	return ret;
+}
+
+extern struct range_tree_node *range_tree_in_range(struct range_tree_root *root,
+							 u64 start, u64 end);
+extern struct range_tree_node *range_tree_in_range_adjacent(
+						struct range_tree_root *root,
+							 u64 start, u64 end);
+extern void range_tree_add(struct range_tree_root *root,
+						struct range_tree_node *node);
+extern void range_tree_remove(struct range_tree_root *root,
+						struct range_tree_node *node);
+#endif
+
+
diff --git a/lib/Makefile b/lib/Makefile
index 18515f0..f43ef0d 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -12,7 +12,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 idr.o int_sqrt.o extable.o prio_tree.o \
 	 sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \
 	 proportions.o prio_heap.o ratelimit.o show_mem.o \
-	 is_single_threaded.o plist.o decompress.o
+	 is_single_threaded.o plist.o decompress.o rangetree.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/rangetree.c b/lib/rangetree.c
new file mode 100644
index 0000000..0f6208a
--- /dev/null
+++ b/lib/rangetree.c
@@ -0,0 +1,105 @@
+#include <linux/rangetree.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+
+
+/**
+ * range_tree_in_range - Returns the first node that overlaps with the
+ *                       given range
+ * @root: range_tree root
+ * @start: range start
+ * @end: range end
+ *
+ */
+struct range_tree_node *range_tree_in_range(struct range_tree_root *root,
+						u64 start, u64 end)
+{
+	struct rb_node **p = &root->head.rb_node;
+	struct range_tree_node *candidate;
+
+	while (*p) {
+		candidate = rb_entry(*p, struct range_tree_node, rb);
+		if (end < candidate->start)
+			p = &(*p)->rb_left;
+		else if (start > candidate->end)
+			p = &(*p)->rb_right;
+		else
+			return candidate;
+	}
+
+	return 0;
+}
+
+
+/**
+ * range_tree_in_range - Returns the first node that overlaps or is adjacent
+ *                       with the given range
+ * @root: range_tree root
+ * @start: range start
+ * @end: range end
+ *
+ */
+struct range_tree_node *range_tree_in_range_adjacent(
+					struct range_tree_root *root,
+					u64 start, u64 end)
+{
+	struct rb_node **p = &root->head.rb_node;
+	struct range_tree_node *candidate;
+
+	while (*p) {
+		candidate = rb_entry(*p, struct range_tree_node, rb);
+		if (end+1 < candidate->start)
+			p = &(*p)->rb_left;
+		else if (start > candidate->end + 1)
+			p = &(*p)->rb_right;
+		else
+			return candidate;
+	}
+	return 0;
+}
+
+/**
+ * range_tree_add - Add a node to a range tree
+ * @root: range tree to be added to
+ * @node: range_tree_node to be added
+ *
+ * Adds a node to the range tree.
+ */
+void range_tree_add(struct range_tree_root *root,
+					struct range_tree_node *node)
+{
+	struct rb_node **p = &root->head.rb_node;
+	struct rb_node *parent = NULL;
+	struct range_tree_node *ptr;
+
+	WARN_ON_ONCE(!RB_EMPTY_NODE(&node->rb));
+
+	while (*p) {
+		parent = *p;
+		ptr = rb_entry(parent, struct range_tree_node, rb);
+		if (node->start < ptr->start)
+			p = &(*p)->rb_left;
+		else
+			p = &(*p)->rb_right;
+	}
+	rb_link_node(&node->rb, parent, p);
+	rb_insert_color(&node->rb, &root->head);
+
+}
+
+
+/**
+ * range_tree_remove: Removes a given node from the tree
+ * @root: root of tree
+ * @node: Node to be removed
+ *
+ * Removes a node and splays the tree
+ */
+void range_tree_remove(struct range_tree_root *root,
+						struct range_tree_node *node)
+{
+	WARN_ON_ONCE(RB_EMPTY_NODE(&node->rb));
+
+	rb_erase(&node->rb, &root->head);
+	RB_CLEAR_NODE(&node->rb);
+}
-- 
1.7.3.2.146.gca209

[PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE flags

[John Stultz]

This patch provides new fadvise flags that can be used to mark
file pages as volatile, which will allow it to be discarded if the
kernel wants to reclaim memory.

This is useful for userspace to allocate things like caches, and lets
the kernel destructively (but safely) reclaim them when there's memory
pressure.

It's different from FADV_DONTNEED since the pages are not immediately
discarded; they are only discarded under pressure.

This is very much influenced by the Android Ashmem interface by
Robert Love so credits to him and the Android developers.
In many cases the code & logic come directly from the ashmem patch.
The intent of this patch is to allow for ashmem-like behavior, but
embeds the idea a little deeper into the VM code, instead of isolating
it into a specific driver.

I'm very much a newbie at the VM code, so At this point, I just want
to try to get some input on the patch, so if you have another idea
for using something other then fadvise, or other thoughts on how the
volatile ranges are stored, I'd be really interested in hearing them.
So let me know if you have any comments for feedback!

Also many thanks to Dave Hansen who helped design and develop the
initial version of this patch, and has provided continued review and
mentoring for me in the VM code.

v2:
* After the valid critique that just dropping pages would poke holes
in volatile ranges, and instead we should zap an entire range if we
drop any of it, I changed the code to more closely mimic the ashmem
implementation, which zaps entire ranges via a shrinker using an lru
list that tracks which range has been marked volatile the longest.

v3:
* Reworked to use range tree implementation.

v4:
* Renamed functions to avoid confusion.
* More consistant PAGE_CACHE_SHIFT usage, suggested by Dmitry
  Adamushko
* Fixes exit without unlocking issue found by Dmitry Adamushko
* Migrate to rbtree based rangetree implementation
* Simplified locking to use global lock (we were grabbing global
  lru lock every time anyway).
* Avoid ENOMEM isses by allocating before we get into complicated
  code.
* Add some documentation to the volatile.c file from Neil Brown

Known issues:
* Lockdep doesn't like calling vmtruncate_range() from a shrinker.
  Any help here on how to address this would be appreciated.
  I've tried switching to invalidate_inode_pages2_range, but
  that always returns EBUSY in my testing, and I don't really
  want to launder dirty pages, instead I want to zap them.
* Concern over bloating the address_space struct

CC: Andrew Morton <akpm@linux-foundation.org>
CC: Android Kernel Team <kernel-team@android.com>
CC: Robert Love <rlove@google.com>
CC: Mel Gorman <mel@csn.ul.ie>
CC: Hugh Dickins <hughd@google.com>
CC: Dave Hansen <dave@linux.vnet.ibm.com>
CC: Rik van Riel <riel@redhat.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Neil Brown <neilb@suse.de>
CC: Andrea Righi <andrea@betterlinux.com>
CC: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 fs/inode.c               |    4 +
 include/linux/fadvise.h  |    5 +
 include/linux/fs.h       |    2 +
 include/linux/volatile.h |   14 ++
 mm/Makefile              |    2 +-
 mm/fadvise.c             |   16 +++-
 mm/volatile.c            |  313 ++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 354 insertions(+), 2 deletions(-)
 create mode 100644 include/linux/volatile.h
 create mode 100644 mm/volatile.c

diff --git a/fs/inode.c b/fs/inode.c
index d3ebdbe..f602dc2 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -27,6 +27,7 @@
 #include <linux/cred.h>
 #include <linux/buffer_head.h> /* for inode_has_buffers */
 #include <linux/ratelimit.h>
+#include <linux/volatile.h>
 #include "internal.h"
 
 /*
@@ -254,6 +255,7 @@ void __destroy_inode(struct inode *inode)
 	if (inode->i_default_acl && inode->i_default_acl != ACL_NOT_CACHED)
 		posix_acl_release(inode->i_default_acl);
 #endif
+	mapping_clear_volatile_ranges(&inode->i_data);
 	this_cpu_dec(nr_inodes);
 }
 EXPORT_SYMBOL(__destroy_inode);
@@ -360,6 +362,8 @@ void address_space_init_once(struct address_space *mapping)
 	spin_lock_init(&mapping->private_lock);
 	INIT_RAW_PRIO_TREE_ROOT(&mapping->i_mmap);
 	INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
+	range_tree_init(&mapping->volatile_root);
+
 }
 EXPORT_SYMBOL(address_space_init_once);
 
diff --git a/include/linux/fadvise.h b/include/linux/fadvise.h
index e8e7471..443951c 100644
--- a/include/linux/fadvise.h
+++ b/include/linux/fadvise.h
@@ -18,4 +18,9 @@
 #define POSIX_FADV_NOREUSE	5 /* Data will be accessed once.  */
 #endif
 
+#define POSIX_FADV_VOLATILE	8  /* _can_ toss, but don't toss now */
+#define POSIX_FADV_NONVOLATILE	9  /* Remove VOLATILE flag */
+
+
+
 #endif	/* FADVISE_H_INCLUDED */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 69cd5bb..2e20be1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -10,6 +10,7 @@
 #include <linux/ioctl.h>
 #include <linux/blk_types.h>
 #include <linux/types.h>
+#include <linux/rangetree.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -655,6 +656,7 @@ struct address_space {
 	spinlock_t		private_lock;	/* for use by the address_space */
 	struct list_head	private_list;	/* ditto */
 	struct address_space	*assoc_mapping;	/* ditto */
+	struct range_tree_root	volatile_root;	/* volatile range list */
 } __attribute__((aligned(sizeof(long))));
 	/*
 	 * On most architectures that alignment is already the case; but
diff --git a/include/linux/volatile.h b/include/linux/volatile.h
new file mode 100644
index 0000000..5460d7b
--- /dev/null
+++ b/include/linux/volatile.h
@@ -0,0 +1,14 @@
+#ifndef _LINUX_VOLATILE_H
+#define _LINUX_VOLATILE_H
+
+#include <linux/fs.h>
+
+extern long mapping_range_volatile(struct address_space *mapping,
+				pgoff_t start_index, pgoff_t end_index);
+extern long mapping_range_nonvolatile(struct address_space *mapping,
+				pgoff_t start_index, pgoff_t end_index);
+extern long mapping_range_isvolatile(struct address_space *mapping,
+				pgoff_t start_index, pgoff_t end_index);
+extern void mapping_clear_volatile_ranges(struct address_space *mapping);
+
+#endif /* _LINUX_VOLATILE_H */
diff --git a/mm/Makefile b/mm/Makefile
index 50ec00e..7b6c7a8 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -13,7 +13,7 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
 			   page_isolation.o mm_init.o mmu_context.o percpu.o \
-			   $(mmu-y)
+			   volatile.o $(mmu-y)
 obj-y += init-mm.o
 
 ifdef CONFIG_NO_BOOTMEM
diff --git a/mm/fadvise.c b/mm/fadvise.c
index 469491e0..3e33845 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -17,6 +17,7 @@
 #include <linux/fadvise.h>
 #include <linux/writeback.h>
 #include <linux/syscalls.h>
+#include <linux/volatile.h>
 
 #include <asm/unistd.h>
 
@@ -106,7 +107,7 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
 		nrpages = end_index - start_index + 1;
 		if (!nrpages)
 			nrpages = ~0UL;
-		
+
 		ret = force_page_cache_readahead(mapping, file,
 				start_index,
 				nrpages);
@@ -128,6 +129,19 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
 			invalidate_mapping_pages(mapping, start_index,
 						end_index);
 		break;
+	case POSIX_FADV_VOLATILE:
+		/* First and last PARTIAL page! */
+		start_index = offset >> PAGE_CACHE_SHIFT;
+		end_index = endbyte >> PAGE_CACHE_SHIFT;
+		ret = mapping_range_volatile(mapping, start_index, end_index);
+		break;
+	case POSIX_FADV_NONVOLATILE:
+		/* First and last PARTIAL page! */
+		start_index = offset >> PAGE_CACHE_SHIFT;
+		end_index = endbyte >> PAGE_CACHE_SHIFT;
+		ret = mapping_range_nonvolatile(mapping, start_index,
+								end_index);
+		break;
 	default:
 		ret = -EINVAL;
 	}
diff --git a/mm/volatile.c b/mm/volatile.c
new file mode 100644
index 0000000..e412a8b
--- /dev/null
+++ b/mm/volatile.c
@@ -0,0 +1,313 @@
+/* mm/volatile.c
+ *
+ * Volatile page range managment.
+ *      Copyright 2011 Linaro
+ *
+ * Based on mm/ashmem.c
+ *      by Robert Love <rlove@google.com>
+ *      Copyright (C) 2008 Google, Inc.
+ *
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * 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.
+ *
+ *
+ * The goal behind volatile ranges is to allow applications to interact
+ * with the kernel's cache management infrastructure.  In particular an
+ * application can say "this memory contains data that might be useful in
+ * the future, but can be reconstructed if necessary, so if the kernel
+ * needs, it can zap and reclaim this memory without having to swap it out.
+ *
+ * The proposed mechanism - at a high level - is for user-space to be able
+ * to say "This memory is volatile" and then later "this memory is no longer
+ * volatile".  If the content of the memory is still available the second
+ * request succeeds.  If not, the memory is marked non-volatile and an
+ * error is returned to denote that the contents have been lost.
+ *
+ * Credits to Neil Brown for the above description.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/pagemap.h>
+#include <linux/volatile.h>
+
+static DEFINE_MUTEX(volatile_mutex);
+
+struct volatile_range {
+	struct list_head lru;
+	struct range_tree_node range_node;
+
+	unsigned int purged;
+	struct address_space *mapping;
+};
+
+/* LRU list of volatile page ranges */
+static LIST_HEAD(volatile_lru_list);
+
+/* Count of pages on our LRU list */
+static u64 lru_count;
+
+
+static inline u64 range_size(struct volatile_range *range)
+{
+	return range->range_node.end - range->range_node.start + 1;
+}
+
+static inline void lru_add(struct volatile_range *range)
+{
+	list_add_tail(&range->lru, &volatile_lru_list);
+	lru_count += range_size(range);
+}
+
+static inline void lru_del(struct volatile_range *range)
+{
+	list_del(&range->lru);
+	lru_count -= range_size(range);
+}
+
+#define range_on_lru(range) (!(range)->purged)
+
+
+static inline void volatile_range_resize(struct volatile_range *range,
+				pgoff_t start_index, pgoff_t end_index)
+{
+	size_t pre = range_size(range);
+
+	range->range_node.start = start_index;
+	range->range_node.end = end_index;
+
+	if (range_on_lru(range))
+		lru_count -= pre - range_size(range);
+}
+
+static struct volatile_range *vrange_alloc(void)
+{
+	struct volatile_range *new;
+
+	new = kzalloc(sizeof(struct volatile_range), GFP_KERNEL);
+	if (!new)
+		return 0;
+	range_tree_node_init(&new->range_node);
+	return new;
+}
+
+static void vrange_del(struct volatile_range *vrange)
+{
+	struct address_space *mapping;
+	mapping = vrange->mapping;
+
+	if (range_on_lru(vrange))
+		lru_del(vrange);
+	range_tree_remove(&mapping->volatile_root, &vrange->range_node);
+	kfree(vrange);
+}
+
+
+
+/*
+ * Mark a region as volatile, allowing dirty pages to be purged
+ * under memory pressure
+ */
+long mapping_range_volatile(struct address_space *mapping,
+				pgoff_t start_index, pgoff_t end_index)
+{
+	struct volatile_range *new;
+	struct range_tree_node *node;
+
+	u64 start, end;
+	int purged = 0;
+	start = (u64)start_index;
+	end = (u64)end_index;
+
+	new = vrange_alloc();
+	if (!new)
+		return -ENOMEM;
+
+	mutex_lock(&volatile_mutex);
+
+	node = range_tree_in_range_adjacent(&mapping->volatile_root,
+						start, end);
+	while (node) {
+		struct volatile_range *vrange;
+
+		/* Already entirely marked volatile, so we're done */
+		if (node->start < start && node->end > end) {
+			/* don't need the allocated value */
+			kfree(new);
+			goto out;
+		}
+
+		/* Grab containing volatile range */
+		vrange = container_of(node, struct volatile_range, range_node);
+
+		/* resize range */
+		start = min_t(u64, start, node->start);
+		end = max_t(u64, end, node->end);
+		purged |= vrange->purged;
+
+
+		vrange_del(vrange);
+
+		/* get the next possible overlap */
+		node = range_tree_in_range(&mapping->volatile_root, start, end);
+	}
+
+	new->mapping = mapping;
+	new->range_node.start = start;
+	new->range_node.end = end;
+	new->purged = purged;
+
+	range_tree_add(&mapping->volatile_root, &new->range_node);
+	if (range_on_lru(new))
+		lru_add(new);
+
+out:
+	mutex_unlock(&volatile_mutex);
+
+	return 0;
+}
+
+/*
+ * Mark a region as nonvolatile, returns 1 if any pages in the region
+ * were purged.
+ */
+long mapping_range_nonvolatile(struct address_space *mapping,
+				pgoff_t start_index, pgoff_t end_index)
+{
+	struct volatile_range *new;
+	struct range_tree_node *node;
+	int ret  = 0;
+	u64 start, end;
+	int used_new = 0;
+
+
+	start = (u64)start_index;
+	end = (u64)end_index;
+
+	/* create new node */
+	new = vrange_alloc();
+	if (!new)
+		return -ENOMEM;
+
+	mutex_lock(&volatile_mutex);
+	node = range_tree_in_range(&mapping->volatile_root, start, end);
+	while (node) {
+		struct volatile_range *vrange;
+		vrange = container_of(node, struct volatile_range, range_node);
+
+
+		ret |= vrange->purged;
+
+		if (start <= node->start && end >= node->end) {
+			vrange_del(vrange);
+		} else if (node->start >= start) {
+			volatile_range_resize(vrange, end+1, node->end);
+		} else if (node->end <= end) {
+			volatile_range_resize(vrange, node->start, start-1);
+		} else {
+			/* we only do this once */
+			used_new = 1;
+			new->mapping = mapping;
+			new->range_node.start = end + 1;
+			new->range_node.end = node->end;
+			volatile_range_resize(vrange, node->start, start-1);
+			range_tree_add(&mapping->volatile_root,
+						&new->range_node);
+			if (range_on_lru(new))
+				lru_add(new);
+
+			break;
+		}
+		node = range_tree_in_range(&mapping->volatile_root, start, end);
+	}
+	mutex_unlock(&volatile_mutex);
+
+	if (!used_new)
+		kfree(new);
+
+	return ret;
+}
+
+
+/*
+ * Cleans up any volatile ranges.
+ */
+void mapping_clear_volatile_ranges(struct address_space *mapping)
+{
+	struct volatile_range *tozap;
+
+	mutex_lock(&volatile_mutex);
+	while (!range_tree_empty(&mapping->volatile_root)) {
+		struct range_tree_node *tmp;
+		tmp = range_tree_root_node(&mapping->volatile_root);
+		tozap = container_of(tmp, struct volatile_range, range_node);
+		vrange_del(tozap);
+
+	}
+	mutex_unlock(&volatile_mutex);
+}
+
+/*
+ * Purges volatile ranges when under memory pressure
+ */
+static int volatile_shrink(struct shrinker *ignored, struct shrink_control *sc)
+{
+	struct volatile_range *range, *next;
+	unsigned long nr_to_scan = sc->nr_to_scan;
+	const gfp_t gfp_mask = sc->gfp_mask;
+
+	if (nr_to_scan && !(gfp_mask & __GFP_FS))
+		return -1;
+	if (!nr_to_scan)
+		return lru_count;
+
+	mutex_lock(&volatile_mutex);
+	list_for_each_entry_safe(range, next, &volatile_lru_list, lru) {
+		struct inode *inode;
+		loff_t start, end;
+
+		inode = range->mapping->host;
+
+		start = range->range_node.start << PAGE_CACHE_SHIFT;
+		end = ((range->range_node.end + 1) << PAGE_CACHE_SHIFT) - 1;
+
+		/*
+		 * XXX - calling vmtruncate_range from a shrinker causes
+		 * lockdep warnings. Revisit this!
+		 */
+		if (!vmtruncate_range(inode, start, end)) {
+			lru_del(range);
+			range->purged = 1;
+			nr_to_scan -= range_size(range);
+		}
+
+		if (nr_to_scan <= 0)
+			break;
+	}
+	mutex_unlock(&volatile_mutex);
+
+	return lru_count;
+}
+
+static struct shrinker volatile_shrinker = {
+	.shrink = volatile_shrink,
+	.seeks = DEFAULT_SEEKS,
+};
+
+static int __init volatile_init(void)
+{
+	register_shrinker(&volatile_shrinker);
+	return 0;
+}
+
+arch_initcall(volatile_init);
-- 
1.7.3.2.146.gca209

[PATCH] fadvise volatile fixes from Dmitry

[John Stultz]

On 03/16/2012 03:51 PM, John Stultz wrote:
> This patch provides new fadvise flags that can be used to mark
> file pages as volatile, which will allow it to be discarded if the
> kernel wants to reclaim memory.
Right after sending this I realized I had forgotten to include
some fixes for issues Dmitry pointed out. So I've included them
here.

Signed-off-by: John Stultz<john.stultz@linaro.org>
---
  mm/volatile.c |    5 +++--
  1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/volatile.c b/mm/volatile.c
index e412a8b..f40c02e 100644
--- a/mm/volatile.c
+++ b/mm/volatile.c
@@ -220,11 +220,12 @@ long mapping_range_nonvolatile(struct address_space *mapping,
  			new->mapping = mapping;
  			new->range_node.start = end + 1;
  			new->range_node.end = node->end;
-			volatile_range_resize(vrange, node->start, start-1);
+			new->purged = vrange->purged;
  			range_tree_add(&mapping->volatile_root,
  						&new->range_node);
  			if (range_on_lru(new))
  				lru_add(new);
+			volatile_range_resize(vrange, node->start, start-1);

  			break;
  		}
@@ -263,7 +264,7 @@ void mapping_clear_volatile_ranges(struct address_space *mapping)
  static int volatile_shrink(struct shrinker *ignored, struct shrink_control *sc)
  {
  	struct volatile_range *range, *next;
-	unsigned long nr_to_scan = sc->nr_to_scan;
+	s64 nr_to_scan = sc->nr_to_scan;
  	const gfp_t gfp_mask = sc->gfp_mask;

  	if (nr_to_scan&&  !(gfp_mask&  __GFP_FS))
-- 
1.7.3.2.146.gca209

Re: [PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE flags

[Dmitry Adamushko]

Hi John,

[ ... ]

> +/*
> + * Mark a region as volatile, allowing dirty pages to be purged
> + * under memory pressure
> + */
> +long mapping_range_volatile(struct address_space *mapping,
> +                               pgoff_t start_index, pgoff_t end_index)
> +{
> +       struct volatile_range *new;
> +       struct range_tree_node *node;
> +
> +       u64 start, end;
> +       int purged = 0;
> +       start = (u64)start_index;
> +       end = (u64)end_index;
> +
> +       new = vrange_alloc();
> +       if (!new)
> +               return -ENOMEM;
> +
> +       mutex_lock(&volatile_mutex);
> +
> +       node = range_tree_in_range_adjacent(&mapping->volatile_root,
> +                                               start, end);
> +       while (node) {
> +               struct volatile_range *vrange;
> +
> +               /* Already entirely marked volatile, so we're done */
> +               if (node->start < start && node->end > end) {
> +                       /* don't need the allocated value */
> +                       kfree(new);
> +                       goto out;
> +               }
> +
> +               /* Grab containing volatile range */
> +               vrange = container_of(node, struct volatile_range, range_node);
> +
> +               /* resize range */
> +               start = min_t(u64, start, node->start);
> +               end = max_t(u64, end, node->end);
> +               purged |= vrange->purged;
> +
> +
> +               vrange_del(vrange);
> +
> +               /* get the next possible overlap */
> +               node = range_tree_in_range(&mapping->volatile_root, start, end);

I guess range_tree_in_range_adjacent() should be used here again.
There can be 2 adjacent regions (left and right), and we'll miss one
of them with range_tree_in_range().

Also (as I had already mentioned before), I think that new ranges must
not be merged with the existing "vrange->purged == 1" ranges.
Otherwise, for some use cases, the whole idea of 'volatility' gets
broken. For example, when an application is processing a big buffer in
small consequent chunks (marking a chunk as volatile when done with
it), and the range gets 'purged' by the kernel early in this process
(when it's still small).

-- Dmitry

Re: [PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE flags

[Dmitry Adamushko]

On 17 March 2012 17:21, Dmitry Adamushko <dmitry.adamushko@gmail.com> wrote:
> Hi John,
>
> [ ... ]
>
>> +/*
>> + * Mark a region as volatile, allowing dirty pages to be purged
>> + * under memory pressure
>> + */
>> +long mapping_range_volatile(struct address_space *mapping,
>> +                               pgoff_t start_index, pgoff_t end_index)
>> +{
>> +       struct volatile_range *new;
>> +       struct range_tree_node *node;
>> +
>> +       u64 start, end;
>> +       int purged = 0;
>> +       start = (u64)start_index;
>> +       end = (u64)end_index;
>> +
>> +       new = vrange_alloc();
>> +       if (!new)
>> +               return -ENOMEM;
>> +
>> +       mutex_lock(&volatile_mutex);
>> +
>> +       node = range_tree_in_range_adjacent(&mapping->volatile_root,
>> +                                               start, end);
>> +       while (node) {
>> +               struct volatile_range *vrange;
>> +
>> +               /* Already entirely marked volatile, so we're done */
>> +               if (node->start < start && node->end > end) {
>> +                       /* don't need the allocated value */
>> +                       kfree(new);
>> +                       goto out;
>> +               }
>> +
>> +               /* Grab containing volatile range */
>> +               vrange = container_of(node, struct volatile_range, range_node);
>> +
>> +               /* resize range */
>> +               start = min_t(u64, start, node->start);
>> +               end = max_t(u64, end, node->end);
>> +               purged |= vrange->purged;
>> +
>> +
>> +               vrange_del(vrange);
>> +
>> +               /* get the next possible overlap */
>> +               node = range_tree_in_range(&mapping->volatile_root, start, end);
>
> I guess range_tree_in_range_adjacent() should be used here again.
> There can be 2 adjacent regions (left and right), and we'll miss one
> of them with range_tree_in_range().
>
> Also (as I had already mentioned before), I think that new ranges must
> not be merged with the existing "vrange->purged == 1" ranges.
> Otherwise, for some use cases, the whole idea of 'volatility' gets
> broken. For example, when an application is processing a big buffer in
> small consequent chunks (marking a chunk as volatile when done with
> it), and the range gets 'purged' by the kernel early in this process
> (when it's still small).

Alternatively, we could immediately truncate purged==0 ranges
(including the one for which mapping_range_volatile() is called) when
merging them with purged==1 ranges. This would result in a more
consistent, but perhaps too aggressive behavior.

Let's consider the following use case:

[1, 10] is an existing purged==1 volatile region, and an application
declares [11, 12] as volatile.

1) current approach: [1, 12] a single purged==1 region, where [11, 12]
was not really truncated (and it could have been [11, 100]);

2) aggressive purge-it-all approach: a single [1, 12] purged==1 region.
The newly added region gets truncated even when there is no shortage
of memory at the moment of addition.

3) do-not-merge approach: [1, 10] purged==1 and [11, 12] purged==0
regions; the later is on the lru list.
it adds extra complexities though (e.g. the need to merge purged
ranges in the shrinker code).

But what's more important, do we have a model of application behavior
that is expected to be observed in, say, 90+% of cases? What patterns
are more common?

For example,

1) make_volatile [1, 10] ; ... ; make_volatile [5, 15]   //
overlapping volatile regions
2) make_volatile [1, 10] ; ... ; make_volatile [1, 15]   // explicit merge
3) make_volatile [1, 10] ; ... ; make_volatile [11, 15] // adjacent
volatile regions

I guess (2) and (3) would be more common, and (3) even more so with
independently used regions (say, by different threads). For (3), do we
really want to merge purged==0 regions when they are adjacent? What if
they are used independently? Let's consider this case:

(a) make_volatile [1, 100] ; ... ; (z) make_volatile [101, 102]

(z) region is used much more frequently by the application [
make_nonvolatile -> do-smth -> make_volatile ], and (a) is not used
often - it's volatile most of the time. If we merge both regions when
they are still purged==0, the whole [1, 102] will tend to be at the
end of the LRU list =>
- we miss an opportunity to truncate (a);
- other regions that are more frequently used than (a) get truncated.

In this light, (3) would be better off behaving as if (a) and (z) were
not adjacent, i.e. no merge...

-- Dmitry

Re: [PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE flags

[John Stultz]

On 03/17/2012 09:21 AM, Dmitry Adamushko wrote:
> Hi John,
>
> [ ... ]
>
>> +/*
>> + * Mark a region as volatile, allowing dirty pages to be purged
>> + * under memory pressure
>> + */
>> +long mapping_range_volatile(struct address_space *mapping,
>> +                               pgoff_t start_index, pgoff_t end_index)
>> +{
>> +       struct volatile_range *new;
>> +       struct range_tree_node *node;
>> +
>> +       u64 start, end;
>> +       int purged = 0;
>> +       start = (u64)start_index;
>> +       end = (u64)end_index;
>> +
>> +       new = vrange_alloc();
>> +       if (!new)
>> +               return -ENOMEM;
>> +
>> +       mutex_lock(&volatile_mutex);
>> +
>> +       node = range_tree_in_range_adjacent(&mapping->volatile_root,
>> +                                               start, end);
>> +       while (node) {
>> +               struct volatile_range *vrange;
>> +
>> +               /* Already entirely marked volatile, so we're done */
>> +               if (node->start<  start&&  node->end>  end) {
>> +                       /* don't need the allocated value */
>> +                       kfree(new);
>> +                       goto out;
>> +               }
>> +
>> +               /* Grab containing volatile range */
>> +               vrange = container_of(node, struct volatile_range, range_node);
>> +
>> +               /* resize range */
>> +               start = min_t(u64, start, node->start);
>> +               end = max_t(u64, end, node->end);
>> +               purged |= vrange->purged;
>> +
>> +
>> +               vrange_del(vrange);
>> +
>> +               /* get the next possible overlap */
>> +               node = range_tree_in_range(&mapping->volatile_root, start, end);
> I guess range_tree_in_range_adjacent() should be used here again.
> There can be 2 adjacent regions (left and right), and we'll miss one
> of them with range_tree_in_range().
Good catch, thank you!

> Also (as I had already mentioned before), I think that new ranges must
> not be merged with the existing "vrange->purged == 1" ranges.
> Otherwise, for some use cases, the whole idea of 'volatility' gets
> broken. For example, when an application is processing a big buffer in
> small consequent chunks (marking a chunk as volatile when done with
> it), and the range gets 'purged' by the kernel early in this process
> (when it's still small).
>
I agree that this seems like a much more intelligent way coalesce 
regions.   I hadn't yet implemented it, as I was hoping for some comment 
from the Android folks if there was a specific use for the design they 
selected for ashmem, but I suspect there isn't.

I'll go ahead and integrate this for the next revision.

Thanks again for the feedback!
-john

Re: [PATCH 1/2] [RFC] Range tree implementation

[Dmitry Adamushko]

Hi John,

On 16 March 2012 23:51, John Stultz <john.stultz@linaro.org> wrote:
> After Andrew suggested something like his mumbletree idea
> to better store a list of ranges, I worked on a few different
> approaches, and this is what I've finally managed to get working.
>
> I suspect range-tree isn't a totally accurate name, but I
> couldn't quite make out the difference between range trees
> and interval trees, so I just picked one to call it. Do
> let me know if you have a better name.
>
> The idea of storing ranges in a tree is nice, but has a number
> of complications. When adding a range, its possible that a
> large range will consume and merge a number of smaller ranges.

Have you considered using 'prio_tree' (include/linux/prio_tree.h)? If
we aim at addressing a wide range of possible use-cases (different
patterns of adding/removing volatile ranges), then, at first glance,
prio_tree looks like a better approach.

e.g. for the "consume and merge a number of smaller ranges" scenario
above, prio_tree gives O(log n) [ O(log n + m) ] behavior iso O(m log
n) in your case.

--Dmitry

Re: [PATCH 1/2] [RFC] Range tree implementation

[Aneesh Kumar K.V]

John Stultz <john.stultz@linaro.org> writes:


....

> +/**
> + * range_tree_in_range - Returns the first node that overlaps with the
> + *                       given range
> + * @root: range_tree root
> + * @start: range start
> + * @end: range end
> + *
> + */
> +struct range_tree_node *range_tree_in_range(struct range_tree_root *root,
> +						u64 start, u64 end)
> +{
> +	struct rb_node **p = &root->head.rb_node;
> +	struct range_tree_node *candidate;
> +
> +	while (*p) {
> +		candidate = rb_entry(*p, struct range_tree_node, rb);
> +		if (end < candidate->start)
> +			p = &(*p)->rb_left;
> +		else if (start > candidate->end)
> +			p = &(*p)->rb_right;
> +		else
> +			return candidate;
> +	}
> +
> +	return 0;


return NULL ?

> +}
> +
> +
> +/**
> + * range_tree_in_range - Returns the first node that overlaps or is adjacent
> + *                       with the given range
> + * @root: range_tree root
> + * @start: range start
> + * @end: range end
> + *
> + */


The comment needs update 

> +struct range_tree_node *range_tree_in_range_adjacent(
> +					struct range_tree_root *root,
> +					u64 start, u64 end)
> +{
> +	struct rb_node **p = &root->head.rb_node;
> +	struct range_tree_node *candidate;
> +
> +	while (*p) {
> +		candidate = rb_entry(*p, struct range_tree_node, rb);
> +		if (end+1 < candidate->start)
> +			p = &(*p)->rb_left;
> +		else if (start > candidate->end + 1)
> +			p = &(*p)->rb_right;
> +		else
> +			return candidate;
> +	}
> +	return 0;
> +}
> +


Below is my hack to get hugetlbfs code converted. The patch compiles.
Will test and send a signed-off-by version later.

not-signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

 fs/hugetlbfs/inode.c    |    3 +-
 include/linux/hugetlb.h |    2 +
 mm/hugetlb.c            |  291 ++++++++++++++++++++++-------------------------
 3 files changed, 139 insertions(+), 157 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index ca4fa70..8309f5e 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -455,6 +455,7 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb,
 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 		info = HUGETLBFS_I(inode);
 		mpol_shared_policy_init(&info->policy, NULL);
+		range_tree_init(&info->rg_root);
 		inode->i_op = &hugetlbfs_dir_inode_operations;
 		inode->i_fop = &simple_dir_operations;
 		/* directory inodes start off with i_nlink == 2 (for "." entry) */
@@ -478,7 +479,6 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
 		inode->i_mapping->a_ops = &hugetlbfs_aops;
 		inode->i_mapping->backing_dev_info =&hugetlbfs_backing_dev_info;
 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
-		INIT_LIST_HEAD(&inode->i_mapping->private_list);
 		info = HUGETLBFS_I(inode);
 		/*
 		 * The policy is initialized here even if we are creating a
@@ -488,6 +488,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
 		 * the rb tree will still be empty.
 		 */
 		mpol_shared_policy_init(&info->policy, NULL);
+		range_tree_init(&info->rg_root);
 		switch (mode & S_IFMT) {
 		default:
 			init_special_inode(inode, mode, dev);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 32e948c..b785541a 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -5,6 +5,7 @@
 #include <linux/fs.h>
 #include <linux/hugetlb_inline.h>
 #include <linux/cgroup.h>
+#include <linux/rangetree.h>
 
 struct ctl_table;
 struct user_struct;
@@ -150,6 +151,7 @@ struct hugetlbfs_sb_info {
 
 struct hugetlbfs_inode_info {
 	struct shared_policy policy;
+	struct range_tree_root rg_root;
 	struct inode vfs_inode;
 };
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4e1462d..a83727d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -69,148 +69,94 @@ static DEFINE_SPINLOCK(hugetlb_lock);
  *	down_read(&mm->mmap_sem);
  *	mutex_lock(&hugetlb_instantiation_mutex);
  */
-struct file_region {
-	struct list_head link;
-	long from;
-	long to;
-};
-
-static long region_add(struct list_head *head, long f, long t)
+static long region_chg(struct range_tree_root *rg_root, long start, long end,
+		       struct range_tree_node **rg_nodep)
 {
-	struct file_region *rg, *nrg, *trg;
+	long chg = 0;
+	struct range_tree_node *rg_node;
 
-	/* Locate the region we are either in or before. */
-	list_for_each_entry(rg, head, link)
-		if (f <= rg->to)
-			break;
+	rg_node = range_tree_in_range_adjacent(rg_root, start, end);
+	/*
+	 * If we need to allocate a new range_tree_node, we return a charge
+	 * with NULL *rg_node;
+	 */
+	if (rg_node == NULL)
+		return end - start;
 
-	/* Round our left edge to the current segment if it encloses us. */
-	if (f > rg->from)
-		f = rg->from;
+	if (start < rg_node->start)
+		chg +=  rg_node->start - start;
+	if (rg_node->end < end)
+		chg += end - rg_node->end;
 
-	/* Check for and consume any regions we now overlap with. */
-	nrg = rg;
-	list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
-		if (&rg->link == head)
-			break;
-		if (rg->from > t)
-			break;
-
-		/* If this area reaches higher then extend our area to
-		 * include it completely.  If this is not the first area
-		 * which we intend to reuse, free it. */
-		if (rg->to > t)
-			t = rg->to;
-		if (rg != nrg) {
-			list_del(&rg->link);
-			kfree(rg);
-		}
-	}
-	nrg->from = f;
-	nrg->to = t;
-	return 0;
+	*rg_nodep = rg_node;
+	return chg;
 }
 
-static long region_chg(struct list_head *head, long f, long t)
+static void region_add(struct range_tree_root *rg_root, long start, long end,
+		       struct range_tree_node *rg_node)
 {
-	struct file_region *rg, *nrg;
-	long chg = 0;
-
-	/* Locate the region we are before or in. */
-	list_for_each_entry(rg, head, link)
-		if (f <= rg->to)
-			break;
+	if (rg_node == NULL)
+		return;
 
-	/* If we are below the current region then a new region is required.
-	 * Subtle, allocate a new region at the position but make it zero
-	 * size such that we can guarantee to record the reservation. */
-	if (&rg->link == head || t < rg->from) {
-		nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
-		if (!nrg)
-			return -ENOMEM;
-		nrg->from = f;
-		nrg->to   = f;
-		INIT_LIST_HEAD(&nrg->link);
-		list_add(&nrg->link, rg->link.prev);
+	if (start < rg_node->start)
+		rg_node->start = start;
 
-		return t - f;
-	}
+	if (end > rg_node->end)
+		rg_node->end = end;
 
-	/* Round our left edge to the current segment if it encloses us. */
-	if (f > rg->from)
-		f = rg->from;
-	chg = t - f;
-
-	/* Check for and consume any regions we now overlap with. */
-	list_for_each_entry(rg, rg->link.prev, link) {
-		if (&rg->link == head)
-			break;
-		if (rg->from > t)
-			return chg;
-
-		/* We overlap with this area, if it extends further than
-		 * us then we must extend ourselves.  Account for its
-		 * existing reservation. */
-		if (rg->to > t) {
-			chg += rg->to - t;
-			t = rg->to;
-		}
-		chg -= rg->to - rg->from;
-	}
-	return chg;
+	range_tree_add(rg_root, rg_node);
 }
 
-static long region_truncate(struct list_head *head, long end)
+static long region_truncate(struct range_tree_root *rg_root, long off)
 {
-	struct file_region *rg, *trg;
 	long chg = 0;
-
-	/* Locate the region we are either in or before. */
-	list_for_each_entry(rg, head, link)
-		if (end <= rg->to)
-			break;
-	if (&rg->link == head)
-		return 0;
-
-	/* If we are in the middle of a region then adjust it. */
-	if (end > rg->from) {
-		chg = rg->to - end;
-		rg->to = end;
-		rg = list_entry(rg->link.next, typeof(*rg), link);
-	}
-
-	/* Drop any remaining regions. */
-	list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
-		if (&rg->link == head)
-			break;
-		chg += rg->to - rg->from;
-		list_del(&rg->link);
-		kfree(rg);
+	struct rb_node *rb_node;
+
+restart:
+	rb_node = rb_first(&rg_root->head);
+	while (rb_node) {
+		struct range_tree_node *rg_node;
+		rg_node = rb_entry(rb_node, struct range_tree_node, rb);
+		if (rg_node->end <= off) {
+			rb_node = rb_next(rb_node);
+			continue;
+		}
+		if (rg_node->start < off) {
+			chg += rg_node->end - off;
+			rg_node->end = off;
+			rb_node = rb_next(rb_node);
+			continue;
+		}
+		chg += rg_node->end - rg_node->start;
+		rb_erase(rb_node, &rg_root->head);
+		goto restart;
 	}
 	return chg;
 }
 
-static long region_count(struct list_head *head, long f, long t)
+static long region_count(struct range_tree_root *rg_root, long start, long end)
 {
-	struct file_region *rg;
 	long chg = 0;
+	struct rb_node *rb_node;
 
-	/* Locate each segment we overlap with, and count that overlap. */
-	list_for_each_entry(rg, head, link) {
-		int seg_from;
-		int seg_to;
+	rb_node = rb_first(&rg_root->head);
+	while (rb_node) {
+		int seg_from, seg_to;
+		struct range_tree_node *rg_node;
 
-		if (rg->to <= f)
+		rg_node = rb_entry(rb_node, struct range_tree_node, rb);
+		if (rg_node->end <= start) {
+			rb_node = rb_next(rb_node);
 			continue;
-		if (rg->from >= t)
+		}
+		if (rg_node->start >= end)
 			break;
-
-		seg_from = max(rg->from, f);
-		seg_to = min(rg->to, t);
+		seg_from = max(rg_node->start, (u64)start);
+		seg_to = min(rg_node->end, (u64)end);
 
 		chg += seg_to - seg_from;
+		rb_node = rb_next(rb_node);
 	}
-
 	return chg;
 }
 
@@ -302,7 +248,7 @@ static void set_vma_private_data(struct vm_area_struct *vma,
 
 struct resv_map {
 	struct kref refs;
-	struct list_head regions;
+	struct range_tree_root rg_root;
 };
 
 static struct resv_map *resv_map_alloc(void)
@@ -312,7 +258,7 @@ static struct resv_map *resv_map_alloc(void)
 		return NULL;
 
 	kref_init(&resv_map->refs);
-	INIT_LIST_HEAD(&resv_map->regions);
+	range_tree_init(&resv_map->rg_root);
 
 	return resv_map;
 }
@@ -322,7 +268,7 @@ static void resv_map_release(struct kref *ref)
 	struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
 
 	/* Clear out any active regions before we release the map. */
-	region_truncate(&resv_map->regions, 0);
+	region_truncate(&resv_map->rg_root, 0);
 	kfree(resv_map);
 }
 
@@ -980,16 +926,19 @@ static void return_unused_surplus_pages(struct hstate *h,
  * No action is required on failure.
  */
 static long vma_needs_reservation(struct hstate *h,
-			struct vm_area_struct *vma, unsigned long addr)
+				  struct vm_area_struct *vma,
+				  unsigned long addr,
+				  struct range_tree_node **rg_node)
 {
 	struct address_space *mapping = vma->vm_file->f_mapping;
 	struct inode *inode = mapping->host;
+	struct hugetlbfs_inode_info *hinfo = HUGETLBFS_I(inode);
 
+	*rg_node = NULL;
 	if (vma->vm_flags & VM_MAYSHARE) {
 		pgoff_t idx = vma_hugecache_offset(h, vma, addr);
-		return region_chg(&inode->i_mapping->private_list,
-							idx, idx + 1);
 
+		return region_chg(&hinfo->rg_root, idx, idx + 1, rg_node);
 	} else if (!is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
 		return 1;
 
@@ -998,28 +947,34 @@ static long vma_needs_reservation(struct hstate *h,
 		pgoff_t idx = vma_hugecache_offset(h, vma, addr);
 		struct resv_map *reservations = vma_resv_map(vma);
 
-		err = region_chg(&reservations->regions, idx, idx + 1);
+		err = region_chg(&reservations->rg_root, idx, idx + 1, rg_node);
 		if (err < 0)
 			return err;
 		return 0;
 	}
 }
 static void vma_commit_reservation(struct hstate *h,
-			struct vm_area_struct *vma, unsigned long addr)
+				   struct vm_area_struct *vma,
+				   unsigned long addr,
+				   struct range_tree_node *rg_node)
 {
 	struct address_space *mapping = vma->vm_file->f_mapping;
 	struct inode *inode = mapping->host;
+	struct hugetlbfs_inode_info *hinfo = HUGETLBFS_I(inode);
+
+	if (rg_node == NULL)
+		return;
 
 	if (vma->vm_flags & VM_MAYSHARE) {
 		pgoff_t idx = vma_hugecache_offset(h, vma, addr);
-		region_add(&inode->i_mapping->private_list, idx, idx + 1);
+		region_add(&hinfo->rg_root, idx, idx + 1, rg_node);
 
 	} else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
 		pgoff_t idx = vma_hugecache_offset(h, vma, addr);
 		struct resv_map *reservations = vma_resv_map(vma);
 
 		/* Mark this page used in the map. */
-		region_add(&reservations->regions, idx, idx + 1);
+		region_add(&reservations->rg_root, idx, idx + 1, rg_node);
 	}
 }
 
@@ -1027,6 +982,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 				    unsigned long addr, int avoid_reserve)
 {
 	int ret, idx;
+	struct range_tree_node *rg_node;
 	struct hstate *h = hstate_vma(vma);
 	struct page *page;
 	struct mem_cgroup *memcg;
@@ -1042,18 +998,24 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 	 * MAP_NORESERVE mappings may also need pages and quota allocated
 	 * if no reserve mapping overlaps.
 	 */
-	chg = vma_needs_reservation(h, vma, addr);
-	if (chg < 0)
-		return ERR_PTR(-ENOMEM);
-	if (chg)
-		if (hugetlb_get_quota(inode->i_mapping, chg))
-			return ERR_PTR(-ENOSPC);
+	chg = vma_needs_reservation(h, vma, addr, &rg_node);
+	if (chg > 0 && rg_node == NULL) {
+		rg_node = kzalloc(sizeof(*rg_node), GFP_KERNEL);
+		if (rg_node == NULL)
+			return ERR_PTR(-ENOMEM);
+	}
 
+	if (chg) {
+		if (hugetlb_get_quota(inode->i_mapping, chg)) {
+			ret = -ENOSPC;
+			goto err_out;
+		}
+	}
 	ret = mem_cgroup_hugetlb_charge_page(idx, pages_per_huge_page(h),
 					     &memcg);
 	if (ret) {
-		hugetlb_put_quota(inode->i_mapping, chg);
-		return ERR_PTR(-ENOSPC);
+		ret = -ENOSPC;
+		goto err_out_quota;
 	}
 	spin_lock(&hugetlb_lock);
 	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
@@ -1062,21 +1024,26 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 	if (!page) {
 		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
 		if (!page) {
-			mem_cgroup_hugetlb_uncharge_memcg(idx,
-							 pages_per_huge_page(h),
-							 memcg);
-			hugetlb_put_quota(inode->i_mapping, chg);
-			return ERR_PTR(-ENOSPC);
+			ret = -ENOSPC;
+			goto err_out_uncharge;
 		}
 	}
 
 	set_page_private(page, (unsigned long) mapping);
 
-	vma_commit_reservation(h, vma, addr);
+	vma_commit_reservation(h, vma, addr, rg_node);
 	/* update page cgroup details */
 	mem_cgroup_hugetlb_commit_charge(idx, pages_per_huge_page(h),
 					 memcg, page);
 	return page;
+
+err_out_uncharge:
+	mem_cgroup_hugetlb_uncharge_memcg(idx, pages_per_huge_page(h), memcg);
+err_out_quota:
+	hugetlb_put_quota(inode->i_mapping, chg);
+err_out:
+	kfree(rg_node);
+	return ERR_PTR(ret);
 }
 
 int __weak alloc_bootmem_huge_page(struct hstate *h)
@@ -2170,7 +2137,7 @@ static void hugetlb_vm_op_close(struct vm_area_struct *vma)
 		end = vma_hugecache_offset(h, vma, vma->vm_end);
 
 		reserve = (end - start) -
-			region_count(&reservations->regions, start, end);
+			region_count(&reservations->rg_root, start, end);
 
 		kref_put(&reservations->refs, resv_map_release);
 
@@ -2697,11 +2664,13 @@ retry:
 	 * any allocations necessary to record that reservation occur outside
 	 * the spinlock.
 	 */
-	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
-		if (vma_needs_reservation(h, vma, address) < 0) {
+	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
+		struct range_tree_node *rg_node;
+		if (vma_needs_reservation(h, vma, address, &rg_node) < 0) {
 			ret = VM_FAULT_OOM;
 			goto backout_unlocked;
 		}
+	}
 
 	spin_lock(&mm->page_table_lock);
 	size = i_size_read(mapping->host) >> huge_page_shift(h);
@@ -2789,7 +2758,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * consumed.
 	 */
 	if ((flags & FAULT_FLAG_WRITE) && !pte_write(entry)) {
-		if (vma_needs_reservation(h, vma, address) < 0) {
+		struct range_tree_node *rg_node;
+		if (vma_needs_reservation(h, vma, address, &rg_node) < 0) {
 			ret = VM_FAULT_OOM;
 			goto out_mutex;
 		}
@@ -2975,7 +2945,9 @@ int hugetlb_reserve_pages(struct inode *inode,
 					vm_flags_t vm_flags)
 {
 	long ret, chg;
+	struct range_tree_node *rg_node;
 	struct hstate *h = hstate_inode(inode);
+	struct hugetlbfs_inode_info *hinfo = HUGETLBFS_I(inode);
 
 	/*
 	 * Only apply hugepage reservation if asked. At fault time, an
@@ -2992,25 +2964,27 @@ int hugetlb_reserve_pages(struct inode *inode,
 	 * called to make the mapping read-write. Assume !vma is a shm mapping
 	 */
 	if (!vma || vma->vm_flags & VM_MAYSHARE)
-		chg = region_chg(&inode->i_mapping->private_list, from, to);
+		chg = region_chg(&hinfo->rg_root, from, to, &rg_node);
 	else {
 		struct resv_map *resv_map = resv_map_alloc();
 		if (!resv_map)
 			return -ENOMEM;
 
-		chg = to - from;
-
+		chg = region_chg(&resv_map->rg_root, from, to, &rg_node);
 		set_vma_resv_map(vma, resv_map);
 		set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
 	}
-
-	if (chg < 0)
-		return chg;
-
+	if (chg > 0 && rg_node == NULL ) {
+		/* We need allocate a new node */
+		rg_node = kzalloc(sizeof(*rg_node), GFP_KERNEL);
+		if (rg_node == NULL)
+			return -ENOMEM;
+	}
 	/* There must be enough filesystem quota for the mapping */
-	if (hugetlb_get_quota(inode->i_mapping, chg))
-		return -ENOSPC;
-
+	if (hugetlb_get_quota(inode->i_mapping, chg)) {
+		ret = -ENOSPC;
+		goto err_out;
+	}
 	/*
 	 * Check enough hugepages are available for the reservation.
 	 * Hand back the quota if there are not
@@ -3018,7 +2992,7 @@ int hugetlb_reserve_pages(struct inode *inode,
 	ret = hugetlb_acct_memory(h, chg);
 	if (ret < 0) {
 		hugetlb_put_quota(inode->i_mapping, chg);
-		return ret;
+		goto err_out;
 	}
 
 	/*
@@ -3033,14 +3007,19 @@ int hugetlb_reserve_pages(struct inode *inode,
 	 * else has to be done for private mappings here
 	 */
 	if (!vma || vma->vm_flags & VM_MAYSHARE)
-		region_add(&inode->i_mapping->private_list, from, to);
+		region_add(&hinfo->rg_root, from, to, rg_node);
 	return 0;
+err_out:
+	kfree(rg_node);
+	return ret;
 }
 
 void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
 {
 	struct hstate *h = hstate_inode(inode);
-	long chg = region_truncate(&inode->i_mapping->private_list, offset);
+	struct hugetlbfs_inode_info *hinfo = HUGETLBFS_I(inode);
+
+	long chg = region_truncate(&hinfo->rg_root, offset);
 
 	spin_lock(&inode->i_lock);
 	inode->i_blocks -= (blocks_per_huge_page(h) * freed);

Re: [PATCH 1/2] [RFC] Range tree implementation

[John Stultz]

On 03/20/2012 03:00 AM, Dmitry Adamushko wrote:
> Hi John,
>
> On 16 March 2012 23:51, John Stultz<john.stultz@linaro.org>  wrote:
>> After Andrew suggested something like his mumbletree idea
>> to better store a list of ranges, I worked on a few different
>> approaches, and this is what I've finally managed to get working.
>>
>> I suspect range-tree isn't a totally accurate name, but I
>> couldn't quite make out the difference between range trees
>> and interval trees, so I just picked one to call it. Do
>> let me know if you have a better name.
>>
>> The idea of storing ranges in a tree is nice, but has a number
>> of complications. When adding a range, its possible that a
>> large range will consume and merge a number of smaller ranges.
> Have you considered using 'prio_tree' (include/linux/prio_tree.h)? If
> we aim at addressing a wide range of possible use-cases (different
> patterns of adding/removing volatile ranges), then, at first glance,
> prio_tree looks like a better approach.
I'll take a closer look at that!

> e.g. for the "consume and merge a number of smaller ranges" scenario
> above, prio_tree gives O(log n) [ O(log n + m) ] behavior iso O(m log
> n) in your case.
Yea, one of the items I was looking at yesterday was to improve the 
range insert/remove usage, since I end up starting each lookup from the 
root node over and over.  I'm thinking of adding a iterate-next type 
call so that we don't re-start the lookup each iteration of the loop 
once we've found an item.

Thanks again for the great feedback!

-john

Re: [PATCH 0/2] [RFC] Volatile ranges (v4)

[Dmitry Vyukov]

John Stultz <john.stultz <at> linaro.org> writes:
> Ok. So here's another iteration of the fadvise volatile range code.
> 
> I realize this is still a way off from being ready, but I wanted to post
> what I have to share with folks working on the various range/interval
> management ideas as well as update folks who've provided feedback on the
> volatile range code.

Hi John,

May you please confirm whether the fadvise(FADV_VOLATILE)
will work for me in the following case?
I am developing a dynamic data race detector (ThreadSanitizer).
It needs to associate some meta-data (shadow) with each byte
of application memory (4 bytes of shadow for 1 byte of app 
memory). We mmap(MAP_ANONYMOUS|MAP_NORESERVE)
40TB of virtual address space for 
shadow, and then just access it as needed. It works.
But for some apps that consume too much 
memory, it eventually leads to swapping/OOM kills.
There is a property of shadow memory that I would like to exploit
 - any region of shadow memory can be reset to zero at any point
w/o any bad consequences (it can lead to missed data 
races, but it's better than OOM kill).
I've tried to execute madvise(MADV_DONTNEED) every X 
seconds for whole shadow memory. It almost works.
The problem is that madvise() seems to be 
not atomic, occasionally I see missed writes, that's not acceptable,
I need either zero pages or 
consistent pages.
Your FADV_VOLATILE looks like it may be the solution.
To summarize: I have a huge region of memory that
I would like to mark as "volatile" at program 
startup. The region is anonymous (not backed by any file).
The kernel must be able to take away 
any pages in the range, and then return zero pages later.
I do have concurrent writes to the 
range, and missed writes are unacceptable.
Ideally, pages are revoked on LRU basis
TIA

Re: [PATCH 0/2] [RFC] Volatile ranges (v4)

[Dmitry Adamushko]

[ cc: lkml ]

>> > There is a property of shadow memory that I would like to exploit
>> >  - any region of shadow memory can be reset to zero at any point
>> > w/o any bad consequences (it can lead to missed data
>> > races, but it's better than OOM kill).
>> > I've tried to execute madvise(MADV_DONTNEED) every X
>> > seconds for whole shadow memory. It almost works.
>> > The problem is that madvise() seems to be
>> > not atomic, occasionally I see missed writes, that's not acceptable,
>>
>> Just to be sure, you mean that if you do, say
>>
>> *ptr = 1;  // [1]
>> ...
>> value = *ptr; // [2] value is 1 here
>> ...
>> *ptr = 2; // possibly from another thread, but we can be certain that
>> it's after [1], perhaps because we checked the content with [2]
>> ...
>> // madvise(..., MADV_DONTNEED); _might_ have been called
>> ...
>> value = *ptr;
>>
>> so here we expect 'value' to be either 2 or 0 (zero page iff madvise()
>> did take place), but you get '1' occasionally?
>> Is that what you mean or something else?
>
>
>
> Yes, that's what I mean.
> Basically I observed inconsistent state of memory that must never happen. I
> had no other explanations except that the madvise() call works as a time
> machine. I executed madvise() every 3 seconds, and the inconsistencies
> happened exactly at the same times. When I turned off madvise(), the
> problems disappear.

Did you try disabling swapping? The "time machine" (if it's not a
problem somewhere else) should take old stuff from somewhere.

mmap's man indicates "zero-fill-on-demand pages for mappings without
an underlying file" and the comment in madvise_dontneed() says "Be
sure to free swap resources too", but then looking at the code in
zap_pte_ranges(), there are a few corner cases where swap entries seem
to be left over intact. In any case, given that you can reproduce it
easily, it'll be a quick check.

Also, it's a MAP_PRIVATE mapping, isn't it?

>
> I am not sure whether it's a bug or not, because the man says "For the time
> being, the application is finished with the given range", and we are
> obviously do not since we have concurrent accesses. However I would be great
> if it is "fixed".
>
>
>
>> > I need either zero pages or
>> > consistent pages.
>> > Your FADV_VOLATILE looks like it may be the solution.
>> > To summarize: I have a huge region of memory that
>> > I would like to mark as "volatile" at program
>> > startup. The region is anonymous (not backed by any file).
>> > The kernel must be able to take away
>> > any pages in the range, and then return zero pages later.
>>
>> I guess that for the use-cases that people have considered so far,
>> users are supposed to mark regions NONVOLATILE before accessing them
>> again. If I understand correctly, that's not what you want to do...
>
>
> No, it's not what I want to do. I can't do any tracking during accesses.
> Ideally I just mark the range during startup, it's also possible to do some
> work on a periodic basis.
>
>
>>
>> does it mean that your 'transactions' are always write-a-single-word?
>> i.e. you don't need to make sure that, say, in
>>
>> ptr[0] = val_a;
>> ptr[1] = val_b;
>> ... // no accesses to ptr [0] and [1]
>> c = ptr[0];
>> d = ptr[1];
>>
>> either c == val_a and d == val_b or both are 0?
>
>
> Exactly. Any transaction first issues N independent 8-byte atomic reads, and
> then optionally 1 atomic 8-byte write. Value of 0 especially means "no data
> here", because, well, I do not want to setup 40TB of memory to some other
> value :)
>
>
>>
>>
>> Also, the current implementation of volatile-ranges will try to 'zap'
>> the whole volatile range... not just some of its pages. Perhaps, it's
>> not something you need too. Of course, this can be addressed one way
>> or another.
>
>
> Well, yes, it's not ideal (but we had lived with MADV_DONTNEED for the whole
> range for some time). Ideally, kernel just takes pages away as it needs
> them.
>
>
>
>> Basically, in your specific case, the pages of your region should be,
>> kind of, swapped out to /dev/zero :-)) meaning that once the system
>> decides to swap such a page out, no actual swap is required and, once
>> the area is being accessed again, a zero-page is mapped into it.
>
>
> Yes, I believe that's how MADV_DONTNEED currently works (... or
> zero-fill-on-demand pages for mappings without an underlying file).
> Also the pages must be "swapped out" with higher prio.
> I think what I want is somewhat similar to page cache. Kind of best effort
> LRU caching.
>

-- Dmitry