[PATCH 1/5] [RFC] Add volatile range management code

John Stultz
2012-07-28T03:58:05Z

This patch provides the volatile range management code
that filesystems can utilize when implementing
FALLOC_FL_MARK_VOLATILE.

It tracks a collection of page ranges against a mapping
stored in an interval-tree. This code handles coalescing
overlapping and adjacent ranges, as well as splitting
ranges when sub-chunks are removed.

The ranges can be marked purged or unpurged. And there is
a per-fs lru list that tracks all the unpurged ranges for
that fs.

v2:
* Fix bug in volatile_ranges_get_last_used returning bad
start,end values
* Rework for intervaltree renaming
* Optimize volatile_range_lru_size to avoid running through
lru list each time.

v3:
* Improve function name to make it clear what the
volatile_ranges_pluck_lru() code does.
* Drop volatile_range_lru_size and unpurged_page_count
mangement as its now unused

v4:
* Re-add volatile_range_lru_size and unpruged_page_count
* Fix bug in range_remove when we split ranges, we add
an overlapping range before resizing the existing range.

v5:
* Drop intervaltree for prio_tree usage per Michel &
Dmitry's suggestions.
* Cleanups

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>
CC: Mike Hommey <mh@glandium.org>
CC: Jan Kara <jack@suse.cz>
CC: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
CC: Michel Lespinasse <walken@google.com>
CC: Minchan Kim <minchan@kernel.org>
CC: linux-mm@kvack.org <linux-mm@kvack.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
include/linux/volatile.h | 45 ++++
mm/Makefile | 2 +-
mm/volatile.c | 509 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 555 insertions(+), 1 deletion(-)
create mode 100644 include/linux/volatile.h
create mode 100644 mm/volatile.c

diff --git a/include/linux/volatile.h b/include/linux/volatile.h
new file mode 100644
index 0000000..6f41b98
--- /dev/null
+++ b/include/linux/volatile.h
@@ -0,0 +1,45 @@
+#ifndef _LINUX_VOLATILE_H
+#define _LINUX_VOLATILE_H
+
+#include <linux/fs.h>
+
+struct volatile_fs_head {
+ struct mutex lock;
+ struct list_head lru_head;
+ s64 unpurged_page_count;
+};
+
+
+#define DEFINE_VOLATILE_FS_HEAD(name) struct volatile_fs_head name = { \
+ .lock = __MUTEX_INITIALIZER(name.lock), \
+ .lru_head = LIST_HEAD_INIT(name.lru_head), \
+ .unpurged_page_count = 0, \
+}
+
+
+static inline void volatile_range_lock(struct volatile_fs_head *head)
+{
+ mutex_lock(&head->lock);
+}
+
+static inline void volatile_range_unlock(struct volatile_fs_head *head)
+{
+ mutex_unlock(&head->lock);
+}
+
+extern long volatile_range_add(struct volatile_fs_head *head,
+ struct address_space *mapping,
+ pgoff_t start_index, pgoff_t end_index);
+extern long volatile_range_remove(struct volatile_fs_head *head,
+ struct address_space *mapping,
+ pgoff_t start_index, pgoff_t end_index);
+
+extern s64 volatile_range_lru_size(struct volatile_fs_head *head);
+
+extern void volatile_range_clear(struct volatile_fs_head *head,
+ struct address_space *mapping);
+
+extern s64 volatile_ranges_pluck_lru(struct volatile_fs_head *head,
+ struct address_space **mapping,
+ pgoff_t *start, pgoff_t *end);
+#endif /* _LINUX_VOLATILE_H */
diff --git a/mm/Makefile b/mm/Makefile
index 2e2fbbe..3e3cd6f 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -16,7 +16,7 @@ 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 \
- compaction.o $(mmu-y)
+ compaction.o volatile.o $(mmu-y)
obj-y += init-mm.o

ifdef CONFIG_NO_BOOTMEM
diff --git a/mm/volatile.c b/mm/volatile.c
new file mode 100644
index 0000000..d05a767
--- /dev/null
+++ b/mm/volatile.c
@@ -0,0 +1,509 @@
+/* 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 volatile range management is a helper layer on top of the range tree
+ * code, which is used to help filesystems manage page ranges that are volatile.
+ *
+ * These ranges are stored in a per-mapping range tree. Storing both purged and
+ * unpurged ranges connected to that address_space. Unpurged ranges are also
+ * linked together in an lru list that is per-volatile-fs-head (basically
+ * per-filesystem).
+ *
+ * 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>
+#include <linux/rbtree.h>
+#include <linux/hash.h>
+#include <linux/shmem_fs.h>
+
+
+struct volatile_range {
+ struct list_head lru;
+ struct prio_tree_node node;
+ unsigned int purged;
+ struct address_space *mapping;
+};
+
+
+/*
+ * To avoid bloating the address_space structure, we use
+ * a hash structure to map from address_space mappings to
+ * the interval_tree root that stores volatile ranges
+ */
+static DEFINE_MUTEX(hash_mutex);
+static struct hlist_head *mapping_hash;
+static long mapping_hash_shift = 8;
+struct mapping_hash_entry {
+ struct prio_tree_root root;
+ struct address_space *mapping;
+ struct hlist_node hnode;
+};
+
+
+static inline
+struct prio_tree_root *__mapping_to_root(struct address_space *mapping)
+{
+ struct hlist_node *elem;
+ struct mapping_hash_entry *entry;
+ struct prio_tree_root *ret = NULL;
+
+ hlist_for_each_entry_rcu(entry, elem,
+ &mapping_hash[hash_ptr(mapping, mapping_hash_shift)],
+ hnode)
+ if (entry->mapping == mapping)
+ ret = &entry->root;
+
+ return ret;
+}
+
+
+static inline
+struct prio_tree_root *mapping_to_root(struct address_space *mapping)
+{
+ struct prio_tree_root *ret;
+
+ mutex_lock(&hash_mutex);
+ ret = __mapping_to_root(mapping);
+ mutex_unlock(&hash_mutex);
+ return ret;
+}
+
+
+static inline
+struct prio_tree_root *mapping_allocate_root(struct address_space *mapping)
+{
+ struct mapping_hash_entry *entry;
+ struct prio_tree_root *dblchk;
+ struct prio_tree_root *ret = NULL;
+
+ entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+ if (!entry)
+ return NULL;
+
+ mutex_lock(&hash_mutex);
+ /* Since we dropped the lock, double check that no one has
+ * created the same hash entry.
+ */
+ dblchk = __mapping_to_root(mapping);
+ if (dblchk) {
+ kfree(entry);
+ ret = dblchk;
+ goto out;
+ }
+
+ INIT_HLIST_NODE(&entry->hnode);
+ entry->mapping = mapping;
+ INIT_PRIO_TREE_ROOT(&entry->root);
+
+ hlist_add_head_rcu(&entry->hnode,
+ &mapping_hash[hash_ptr(mapping, mapping_hash_shift)]);
+
+ ret = &entry->root;
+out:
+ mutex_unlock(&hash_mutex);
+ return ret;
+}
+
+
+static inline void mapping_free_root(struct prio_tree_root *root)
+{
+ struct mapping_hash_entry *entry;
+
+ mutex_lock(&hash_mutex);
+ entry = container_of(root, struct mapping_hash_entry, root);
+
+ hlist_del_rcu(&entry->hnode);
+ kfree(entry);
+ mutex_unlock(&hash_mutex);
+}
+
+
+/* volatile range helpers */
+static inline void vrange_resize(struct volatile_fs_head *head,
+ struct prio_tree_root *root,
+ struct volatile_range *vrange,
+ pgoff_t start_index, pgoff_t end_index)
+{
+ pgoff_t old_size, new_size;
+
+ old_size = vrange->node.last - vrange->node.start;
+ new_size = end_index-start_index;
+
+ if (!vrange->purged)
+ head->unpurged_page_count += new_size - old_size;
+
+ prio_tree_remove(root, &vrange->node);
+ vrange->node.start = start_index;
+ vrange->node.last = end_index;
+ prio_tree_insert(root, &vrange->node);
+}
+
+static struct volatile_range *vrange_alloc(void)
+{
+ struct volatile_range *new;
+
+ new = kzalloc(sizeof(struct volatile_range), GFP_KERNEL);
+ if (!new)
+ return 0;
+ INIT_PRIO_TREE_NODE(&new->node);
+ return new;
+}
+
+
+static void vrange_add(struct volatile_fs_head *head,
+ struct prio_tree_root *root,
+ struct volatile_range *vrange)
+{
+
+ prio_tree_insert(root, &vrange->node);
+
+ /* Only add unpurged ranges to LRU */
+ if (!vrange->purged) {
+ head->unpurged_page_count += vrange->node.last - vrange->node.start;
+ list_add_tail(&vrange->lru, &head->lru_head);
+ }
+
+}
+
+
+
+static void vrange_del(struct volatile_fs_head *head,
+ struct prio_tree_root *root,
+ struct volatile_range *vrange)
+{
+ if (!vrange->purged) {
+ head->unpurged_page_count -= vrange->node.last - vrange->node.start;
+ list_del(&vrange->lru);
+ }
+ prio_tree_remove(root, &vrange->node);
+ kfree(vrange);
+}
+
+
+/**
+ * volatile_range_add: Marks a page interval as volatile
+ * @head: per-fs volatile head
+ * @mapping: address space who's range is being marked volatile
+ * @start_index: Starting page in range to be marked volatile
+ * @end_index: Ending page in range to be marked volatile
+ *
+ * Mark a region as volatile. Coalesces overlapping and neighboring regions.
+ *
+ * Must lock the volatile_fs_head before calling!
+ *
+ * Returns 1 if the range was coalesced with any purged ranges.
+ * Returns 0 on success.
+ */
+long volatile_range_add(struct volatile_fs_head *head,
+ struct address_space *mapping,
+ pgoff_t start, pgoff_t end)
+{
+ struct prio_tree_node *node;
+ struct prio_tree_iter iter;
+ struct volatile_range *new, *vrange;
+ struct prio_tree_root *root;
+ int purged = 0;
+
+ /* Make sure we're properly locked */
+ WARN_ON(!mutex_is_locked(&head->lock));
+
+ /*
+ * Because the lock might be held in a shrinker, release
+ * it during allocation.
+ */
+ mutex_unlock(&head->lock);
+ new = vrange_alloc();
+ mutex_lock(&head->lock);
+ if (!new)
+ return -ENOMEM;
+
+ root = mapping_to_root(mapping);
+ if (!root) {
+ mutex_unlock(&head->lock);
+ root = mapping_allocate_root(mapping);
+ mutex_lock(&head->lock);
+ if (!root) {
+ kfree(new);
+ return -ENOMEM;
+ }
+ }
+
+
+ /* First, find any existing intervals that overlap */
+ prio_tree_iter_init(&iter, root, start, end);
+ node = prio_tree_next(&iter);
+ while (node) {
+ vrange = container_of(node, struct volatile_range, node);
+
+ /* Already entirely marked volatile, so we're done */
+ if (vrange->node.start < start && vrange->node.last > end) {
+ /* don't need the allocated value */
+ kfree(new);
+ return purged;
+ }
+
+ /* Resize the new range to cover all overlapping ranges */
+ start = min_t(u64, start, vrange->node.start);
+ end = max_t(u64, end, vrange->node.last);
+
+ /* Inherit purged state from overlapping ranges */
+ purged |= vrange->purged;
+
+ /* See if there's a next range that overlaps */
+ node = prio_tree_next(&iter);
+
+ /* Delete the old range, as we consume it */
+ vrange_del(head, root, vrange);
+
+ }
+
+ /* Coalesce left-adjacent ranges */
+ prio_tree_iter_init(&iter, root, start-1, start);
+ node = prio_tree_next(&iter);
+ while (node) {
+ vrange = container_of(node, struct volatile_range, node);
+ node = prio_tree_next(&iter);
+ /* Only coalesce if both are either purged or unpurged */
+ if (vrange->purged == purged) {
+ /* resize new range */
+ start = min_t(u64, start, vrange->node.start);
+ end = max_t(u64, end, vrange->node.last);
+ /* delete old range */
+ vrange_del(head, root, vrange);
+ }
+ }
+
+ /* Coalesce right-adjacent ranges */
+ prio_tree_iter_init(&iter, root, end, end+1);
+ node = prio_tree_next(&iter);
+ while (node) {
+ vrange = container_of(node, struct volatile_range, node);
+ node = prio_tree_next(&iter);
+ /* Only coalesce if both are either purged or unpurged */
+ if (vrange->purged == purged) {
+ /* resize new range */
+ start = min_t(u64, start, vrange->node.start);
+ end = max_t(u64, end, vrange->node.last);
+ /* delete old range */
+ vrange_del(head, root, vrange);
+ }
+ }
+ /* Assign and store the new range in the range tree */
+ new->mapping = mapping;
+ new->node.start = start;
+ new->node.last = end;
+ new->purged = purged;
+ vrange_add(head, root, new);
+
+ return purged;
+}
+
+
+/**
+ * volatile_range_remove: Marks a page interval as nonvolatile
+ * @head: per-fs volatile head
+ * @mapping: address space who's range is being marked nonvolatile
+ * @start_index: Starting page in range to be marked nonvolatile
+ * @end_index: Ending page in range to be marked nonvolatile
+ *
+ * Mark a region as nonvolatile. And remove any contained pages
+ * from the volatile range tree.
+ *
+ * Must lock the volatile_fs_head before calling!
+ *
+ * Returns 1 if any portion of the range was purged.
+ * Returns 0 on success.
+ */
+long volatile_range_remove(struct volatile_fs_head *head,
+ struct address_space *mapping,
+ pgoff_t start, pgoff_t end)
+{
+ struct prio_tree_node *node;
+ struct prio_tree_iter iter;
+ struct volatile_range *new, *vrange;
+ struct prio_tree_root *root;
+ int ret = 0;
+ int used_new = 0;
+
+ /* Make sure we're properly locked */
+ WARN_ON(!mutex_is_locked(&head->lock));
+
+ /*
+ * Because the lock might be held in a shrinker, release
+ * it during allocation.
+ */
+ mutex_unlock(&head->lock);
+ new = vrange_alloc();
+ mutex_lock(&head->lock);
+ if (!new)
+ return -ENOMEM;
+
+ root = mapping_to_root(mapping);
+ if (!root)
+ goto out;
+
+
+ /* Find any overlapping ranges */
+ prio_tree_iter_init(&iter, root, start, end);
+ node = prio_tree_next(&iter);
+ while (node) {
+ vrange = container_of(node, struct volatile_range, node);
+ node = prio_tree_next(&iter);
+
+ ret |= vrange->purged;
+
+ if (start <= vrange->node.start && end >= vrange->node.last) {
+ /* delete: volatile range is totally within range */
+ vrange_del(head, root, vrange);
+ } else if (vrange->node.start >= start) {
+ /* resize: volatile range right-overlaps range */
+ vrange_resize(head, root, vrange, end+1, vrange->node.last);
+ } else if (vrange->node.last <= end) {
+ /* resize: volatile range left-overlaps range */
+ vrange_resize(head, root, vrange, vrange->node.start, start-1);
+ } else {
+ /* split: range is totally within a volatile range */
+ used_new = 1; /* we only do this once */
+ new->mapping = mapping;
+ new->node.start = end + 1;
+ new->node.last = vrange->node.last;
+ new->purged = vrange->purged;
+ vrange_resize(head, root, vrange, vrange->node.start, start-1);
+ vrange_add(head, root, new);
+ break;
+ }
+ }
+
+out:
+ if (!used_new)
+ kfree(new);
+
+ return ret;
+}
+
+/**
+ * volatile_range_lru_size: Returns the number of unpurged pages on the lru
+ * @head: per-fs volatile head
+ *
+ * Returns the number of unpurged pages on the LRU
+ *
+ * Must lock the volatile_fs_head before calling!
+ *
+ */
+s64 volatile_range_lru_size(struct volatile_fs_head *head)
+{
+ WARN_ON(!mutex_is_locked(&head->lock));
+ return head->unpurged_page_count;
+}
+
+
+/**
+ * volatile_ranges_pluck_lru: Returns mapping and size of lru unpurged range
+ * @head: per-fs volatile head
+ * @mapping: dbl pointer to mapping who's range is being purged
+ * @start: Pointer to starting address of range being purged
+ * @end: Pointer to ending address of range being purged
+ *
+ * Returns the mapping, start and end values of the least recently used
+ * range. Marks the range as purged and removes it from the LRU.
+ *
+ * Must lock the volatile_fs_head before calling!
+ *
+ * Returns 1 on success if a range was returned
+ * Return 0 if no ranges were found.
+ */
+s64 volatile_ranges_pluck_lru(struct volatile_fs_head *head,
+ struct address_space **mapping,
+ pgoff_t *start, pgoff_t *end)
+{
+ struct volatile_range *range;
+
+ WARN_ON(!mutex_is_locked(&head->lock));
+
+ if (list_empty(&head->lru_head))
+ return 0;
+
+ range = list_first_entry(&head->lru_head, struct volatile_range, lru);
+
+ *start = range->node.start;
+ *end = range->node.last;
+ *mapping = range->mapping;
+
+ head->unpurged_page_count -= *end - *start;
+ list_del(&range->lru);
+ range->purged = 1;
+
+ return 1;
+}
+
+
+/*
+ * Cleans up any volatile ranges.
+ */
+void volatile_range_clear(struct volatile_fs_head *head,
+ struct address_space *mapping)
+{
+ struct volatile_range *tozap;
+ struct prio_tree_root *root;
+
+ WARN_ON(!mutex_is_locked(&head->lock));
+
+ root = mapping_to_root(mapping);
+ if (!root)
+ return;
+
+ while (!prio_tree_empty(root)) {
+ tozap = container_of(root->prio_tree_node, struct volatile_range, node);
+ vrange_del(head, root, tozap);
+ }
+ mapping_free_root(root);
+}
+
+
+static int __init volatile_init(void)
+{
+ int i, size;
+
+ size = 1U << mapping_hash_shift;
+ mapping_hash = kzalloc(sizeof(mapping_hash)*size, GFP_KERNEL);
+ for (i = 0; i < size; i++)
+ INIT_HLIST_HEAD(&mapping_hash[i]);
+
+ return 0;
+}
+arch_initcall(volatile_init);
--
1.7.9.5