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authorMel Gorman <mgorman@suse.de>2012-01-12 17:19:34 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-12 20:13:09 -0800
commitb969c4ab9f182a6e1b2a0848be349f99714947b0 (patch)
treedc1c6e4375cfec7b15f13a37307eba8a9e07f40f
parent7335084d446b83cbcb15da80497d03f0c1dc9e21 (diff)
downloadlinaro-lsk-b969c4ab9f182a6e1b2a0848be349f99714947b0.tar.gz
mm: compaction: determine if dirty pages can be migrated without blocking within ->migratepage
Asynchronous compaction is used when allocating transparent hugepages to avoid blocking for long periods of time. Due to reports of stalling, there was a debate on disabling synchronous compaction but this severely impacted allocation success rates. Part of the reason was that many dirty pages are skipped in asynchronous compaction by the following check; if (PageDirty(page) && !sync && mapping->a_ops->migratepage != migrate_page) rc = -EBUSY; This skips over all mapping aops using buffer_migrate_page() even though it is possible to migrate some of these pages without blocking. This patch updates the ->migratepage callback with a "sync" parameter. It is the responsibility of the callback to fail gracefully if migration would block. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: Dave Jones <davej@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Andy Isaacson <adi@hexapodia.org> Cc: Nai Xia <nai.xia@gmail.com> Cc: Johannes Weiner <jweiner@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/btrfs/disk-io.c4
-rw-r--r--fs/hugetlbfs/inode.c3
-rw-r--r--fs/nfs/internal.h2
-rw-r--r--fs/nfs/write.c4
-rw-r--r--include/linux/fs.h9
-rw-r--r--include/linux/migrate.h2
-rw-r--r--mm/migrate.c129
7 files changed, 106 insertions, 47 deletions
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f99a099a774..1375494c8cb 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -872,7 +872,7 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
#ifdef CONFIG_MIGRATION
static int btree_migratepage(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page, bool sync)
{
/*
* we can't safely write a btree page from here,
@@ -887,7 +887,7 @@ static int btree_migratepage(struct address_space *mapping,
if (page_has_private(page) &&
!try_to_release_page(page, GFP_KERNEL))
return -EAGAIN;
- return migrate_page(mapping, newpage, page);
+ return migrate_page(mapping, newpage, page, sync);
}
#endif
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index e425ad9d049..06fd4608a99 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -583,7 +583,8 @@ static int hugetlbfs_set_page_dirty(struct page *page)
}
static int hugetlbfs_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page,
+ bool sync)
{
int rc;
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 5ee92538b06..114398a1583 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -332,7 +332,7 @@ void nfs_commit_release_pages(struct nfs_write_data *data);
#ifdef CONFIG_MIGRATION
extern int nfs_migrate_page(struct address_space *,
- struct page *, struct page *);
+ struct page *, struct page *, bool);
#else
#define nfs_migrate_page NULL
#endif
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 0c3885255f9..889e98bc5a2 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1688,7 +1688,7 @@ out_error:
#ifdef CONFIG_MIGRATION
int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
- struct page *page)
+ struct page *page, bool sync)
{
/*
* If PagePrivate is set, then the page is currently associated with
@@ -1703,7 +1703,7 @@ int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
nfs_fscache_release_page(page, GFP_KERNEL);
- return migrate_page(mapping, newpage, page);
+ return migrate_page(mapping, newpage, page, sync);
}
#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a7409bc157e..b92b73d0b2b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -609,9 +609,12 @@ struct address_space_operations {
loff_t offset, unsigned long nr_segs);
int (*get_xip_mem)(struct address_space *, pgoff_t, int,
void **, unsigned long *);
- /* migrate the contents of a page to the specified target */
+ /*
+ * migrate the contents of a page to the specified target. If sync
+ * is false, it must not block.
+ */
int (*migratepage) (struct address_space *,
- struct page *, struct page *);
+ struct page *, struct page *, bool);
int (*launder_page) (struct page *);
int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
unsigned long);
@@ -2537,7 +2540,7 @@ extern int generic_check_addressable(unsigned, u64);
#ifdef CONFIG_MIGRATION
extern int buffer_migrate_page(struct address_space *,
- struct page *, struct page *);
+ struct page *, struct page *, bool);
#else
#define buffer_migrate_page NULL
#endif
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index e39aeecfe9a..14e6d2a8847 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -11,7 +11,7 @@ typedef struct page *new_page_t(struct page *, unsigned long private, int **);
extern void putback_lru_pages(struct list_head *l);
extern int migrate_page(struct address_space *,
- struct page *, struct page *);
+ struct page *, struct page *, bool);
extern int migrate_pages(struct list_head *l, new_page_t x,
unsigned long private, bool offlining,
bool sync);
diff --git a/mm/migrate.c b/mm/migrate.c
index fc391985899..4e86f3bacb8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -216,6 +216,55 @@ out:
pte_unmap_unlock(ptep, ptl);
}
+#ifdef CONFIG_BLOCK
+/* Returns true if all buffers are successfully locked */
+static bool buffer_migrate_lock_buffers(struct buffer_head *head, bool sync)
+{
+ struct buffer_head *bh = head;
+
+ /* Simple case, sync compaction */
+ if (sync) {
+ do {
+ get_bh(bh);
+ lock_buffer(bh);
+ bh = bh->b_this_page;
+
+ } while (bh != head);
+
+ return true;
+ }
+
+ /* async case, we cannot block on lock_buffer so use trylock_buffer */
+ do {
+ get_bh(bh);
+ if (!trylock_buffer(bh)) {
+ /*
+ * We failed to lock the buffer and cannot stall in
+ * async migration. Release the taken locks
+ */
+ struct buffer_head *failed_bh = bh;
+ put_bh(failed_bh);
+ bh = head;
+ while (bh != failed_bh) {
+ unlock_buffer(bh);
+ put_bh(bh);
+ bh = bh->b_this_page;
+ }
+ return false;
+ }
+
+ bh = bh->b_this_page;
+ } while (bh != head);
+ return true;
+}
+#else
+static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
+ bool sync)
+{
+ return true;
+}
+#endif /* CONFIG_BLOCK */
+
/*
* Replace the page in the mapping.
*
@@ -225,7 +274,8 @@ out:
* 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
*/
static int migrate_page_move_mapping(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page,
+ struct buffer_head *head, bool sync)
{
int expected_count;
void **pslot;
@@ -255,6 +305,19 @@ static int migrate_page_move_mapping(struct address_space *mapping,
}
/*
+ * In the async migration case of moving a page with buffers, lock the
+ * buffers using trylock before the mapping is moved. If the mapping
+ * was moved, we later failed to lock the buffers and could not move
+ * the mapping back due to an elevated page count, we would have to
+ * block waiting on other references to be dropped.
+ */
+ if (!sync && head && !buffer_migrate_lock_buffers(head, sync)) {
+ page_unfreeze_refs(page, expected_count);
+ spin_unlock_irq(&mapping->tree_lock);
+ return -EAGAIN;
+ }
+
+ /*
* Now we know that no one else is looking at the page.
*/
get_page(newpage); /* add cache reference */
@@ -409,13 +472,13 @@ EXPORT_SYMBOL(fail_migrate_page);
* Pages are locked upon entry and exit.
*/
int migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page, bool sync)
{
int rc;
BUG_ON(PageWriteback(page)); /* Writeback must be complete */
- rc = migrate_page_move_mapping(mapping, newpage, page);
+ rc = migrate_page_move_mapping(mapping, newpage, page, NULL, sync);
if (rc)
return rc;
@@ -432,28 +495,28 @@ EXPORT_SYMBOL(migrate_page);
* exist.
*/
int buffer_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page, bool sync)
{
struct buffer_head *bh, *head;
int rc;
if (!page_has_buffers(page))
- return migrate_page(mapping, newpage, page);
+ return migrate_page(mapping, newpage, page, sync);
head = page_buffers(page);
- rc = migrate_page_move_mapping(mapping, newpage, page);
+ rc = migrate_page_move_mapping(mapping, newpage, page, head, sync);
if (rc)
return rc;
- bh = head;
- do {
- get_bh(bh);
- lock_buffer(bh);
- bh = bh->b_this_page;
-
- } while (bh != head);
+ /*
+ * In the async case, migrate_page_move_mapping locked the buffers
+ * with an IRQ-safe spinlock held. In the sync case, the buffers
+ * need to be locked now
+ */
+ if (sync)
+ BUG_ON(!buffer_migrate_lock_buffers(head, sync));
ClearPagePrivate(page);
set_page_private(newpage, page_private(page));
@@ -530,10 +593,13 @@ static int writeout(struct address_space *mapping, struct page *page)
* Default handling if a filesystem does not provide a migration function.
*/
static int fallback_migrate_page(struct address_space *mapping,
- struct page *newpage, struct page *page)
+ struct page *newpage, struct page *page, bool sync)
{
- if (PageDirty(page))
+ if (PageDirty(page)) {
+ if (!sync)
+ return -EBUSY;
return writeout(mapping, page);
+ }
/*
* Buffers may be managed in a filesystem specific way.
@@ -543,7 +609,7 @@ static int fallback_migrate_page(struct address_space *mapping,
!try_to_release_page(page, GFP_KERNEL))
return -EAGAIN;
- return migrate_page(mapping, newpage, page);
+ return migrate_page(mapping, newpage, page, sync);
}
/*
@@ -579,29 +645,18 @@ static int move_to_new_page(struct page *newpage, struct page *page,
mapping = page_mapping(page);
if (!mapping)
- rc = migrate_page(mapping, newpage, page);
- else {
+ rc = migrate_page(mapping, newpage, page, sync);
+ else if (mapping->a_ops->migratepage)
/*
- * Do not writeback pages if !sync and migratepage is
- * not pointing to migrate_page() which is nonblocking
- * (swapcache/tmpfs uses migratepage = migrate_page).
+ * Most pages have a mapping and most filesystems provide a
+ * migratepage callback. Anonymous pages are part of swap
+ * space which also has its own migratepage callback. This
+ * is the most common path for page migration.
*/
- if (PageDirty(page) && !sync &&
- mapping->a_ops->migratepage != migrate_page)
- rc = -EBUSY;
- else if (mapping->a_ops->migratepage)
- /*
- * Most pages have a mapping and most filesystems
- * should provide a migration function. Anonymous
- * pages are part of swap space which also has its
- * own migration function. This is the most common
- * path for page migration.
- */
- rc = mapping->a_ops->migratepage(mapping,
- newpage, page);
- else
- rc = fallback_migrate_page(mapping, newpage, page);
- }
+ rc = mapping->a_ops->migratepage(mapping,
+ newpage, page, sync);
+ else
+ rc = fallback_migrate_page(mapping, newpage, page, sync);
if (rc) {
newpage->mapping = NULL;