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Date: Wed, 14 Dec 2011 15:41:27 +0000
From: Mel Gorman <mgorman@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>,
Minchan Kim <minchan.kim@...il.com>,
Dave Jones <davej@...hat.com>, Jan Kara <jack@...e.cz>,
Andy Isaacson <adi@...apodia.org>,
Johannes Weiner <jweiner@...hat.com>,
Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
Nai Xia <nai.xia@...il.com>, Linux-MM <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 05/11] 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@...e.de>
---
fs/btrfs/disk-io.c | 4 +-
fs/hugetlbfs/inode.c | 3 +-
fs/nfs/internal.h | 2 +-
fs/nfs/write.c | 4 +-
include/linux/fs.h | 9 ++-
include/linux/migrate.h | 2 +-
mm/migrate.c | 129 +++++++++++++++++++++++++++++++++-------------
7 files changed, 106 insertions(+), 47 deletions(-)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 632f8f3..896b87a 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 0be5a78..10b9883 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -576,7 +576,8 @@ 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 3f4d957..8d96ed6 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -330,7 +330,7 @@ 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 1dda78d..33475df 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1711,7 +1711,7 @@ 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
@@ -1726,7 +1726,7 @@ 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 e0bc4ff..5f3089c 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);
@@ -2579,7 +2582,7 @@ 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 e39aeec..14e6d2a 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 177aca4..65c12d2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -220,6 +220,55 @@ 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.
*
@@ -229,7 +278,8 @@ 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;
@@ -259,6 +309,19 @@ 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 */
@@ -415,13 +478,13 @@ 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;
@@ -438,28 +501,28 @@ 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));
@@ -536,10 +599,13 @@ 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.
@@ -549,7 +615,7 @@ 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);
}
/*
@@ -585,29 +651,18 @@ 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;
--
1.7.3.4
--
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