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authorMel Gorman <mgorman@suse.de>2013-07-03 15:02:30 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 16:07:31 -0700
commit059285a25f30c13ed4f5d91cecd6094b9b20bb7b (patch)
treec13706696692a7cad3a406719fd0f3d0f43c17a7 /fs/cachefiles
parent13f7f78981e49f288d871bb918545ef5c952e00b (diff)
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mm: activate !PageLRU pages on mark_page_accessed if page is on local pagevec
If a page is on a pagevec then it is !PageLRU and mark_page_accessed() may fail to move a page to the active list as expected. Now that the LRU is selected at LRU drain time, mark pages PageActive if they are on the local pagevec so it gets moved to the correct list at LRU drain time. Using a debugging patch it was found that for a simple git checkout based workload that pages were never added to the active file list in practice but with this patch applied they are. before after LRU Add Active File 0 750583 LRU Add Active Anon 2640587 2702818 LRU Add Inactive File 8833662 8068353 LRU Add Inactive Anon 207 200 Note that only pages on the local pagevec are considered on purpose. A !PageLRU page could be in the process of being released, reclaimed, migrated or on a remote pagevec that is currently being drained. Marking it PageActive is vunerable to races where PageLRU and Active bits are checked at the wrong time. Page reclaim will trigger VM_BUG_ONs but depending on when the race hits, it could also free a PageActive page to the page allocator and trigger a bad_page warning. Similarly a potential race exists between a per-cpu drain on a pagevec list and an activation on a remote CPU. lru_add_drain_cpu __pagevec_lru_add lru = page_lru(page); mark_page_accessed if (PageLRU(page)) activate_page else SetPageActive SetPageLRU(page); add_page_to_lru_list(page, lruvec, lru); In this case a PageActive page is added to the inactivate list and later the inactive/active stats will get skewed. While the PageActive checks in vmscan could be removed and potentially dealt with, a skew in the statistics would be very difficult to detect. Hence this patch deals just with the common case where a page being marked accessed has just been added to the local pagevec. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Jan Kara <jack@suse.cz> Cc: Rik van Riel <riel@redhat.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Alexey Lyahkov <alexey.lyashkov@gmail.com> Cc: Andrew Perepechko <anserper@ya.ru> Cc: Robin Dong <sanbai@taobao.com> Cc: Theodore Tso <tytso@mit.edu> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Cc: Bernd Schubert <bernd.schubert@fastmail.fm> Cc: David Howells <dhowells@redhat.com> Cc: Trond Myklebust <Trond.Myklebust@netapp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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