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mm: compaction: determine if dirty pages can be migrated without blocking within ->migratepage

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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 <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Dave Jones <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Andy Isaacson <[email protected]>
Cc: Nai Xia <[email protected]>
Cc: Johannes Weiner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Mel Gorman 2012-01-12 17:19:34 -08:00 • committed by Linus Torvalds
commit b969c4ab9f
7 changed files with 106 additions and 47 deletions
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129
mm/migrate.c
View file

@ -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;
@ -254,6 +304,19 @@ static int migrate_page_move_mapping(struct address_space *mapping,
return -EAGAIN;
}
/*
* 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.
*/
@ -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;