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authorMel Gorman <mgorman@suse.de>2014-06-04 16:10:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-04 16:54:10 -0700
commit6fb81a17d21f2a138b8f424af4cf379f2b694060 (patch)
tree01da9c46c9e0d8a6e62b274a48828a462c229eac /mm/swap.c
parente3741b506c5088fa8c911bb5884c430f770fb49d (diff)
mm: do not use unnecessary atomic operations when adding pages to the LRU
When adding pages to the LRU we clear the active bit unconditionally. As the page could be reachable from other paths we cannot use unlocked operations without risk of corruption such as a parallel mark_page_accessed. This patch tests if is necessary to clear the active flag before using an atomic operation. This potentially opens a tiny race when PageActive is checked as mark_page_accessed could be called after PageActive was checked. The race already exists but this patch changes it slightly. The consequence is that that the page may be promoted to the active list that might have been left on the inactive list before the patch. It's too tiny a race and too marginal a consequence to always use atomic operations for. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Jan Kara <jack@suse.cz> Cc: Michal Hocko <mhocko@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap.c')
-rw-r--r--mm/swap.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/mm/swap.c b/mm/swap.c
index 30b6a37c74af..1fb25f8bb155 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -631,13 +631,15 @@ static void __lru_cache_add(struct page *page)
*/
void lru_cache_add_anon(struct page *page)
{
- ClearPageActive(page);
+ if (PageActive(page))
+ ClearPageActive(page);
__lru_cache_add(page);
}
void lru_cache_add_file(struct page *page)
{
- ClearPageActive(page);
+ if (PageActive(page))
+ ClearPageActive(page);
__lru_cache_add(page);
}
EXPORT_SYMBOL(lru_cache_add_file);