• Michal Hocko's avatar
    mm: consider all swapped back pages in used-once logic · e4898273
    Michal Hocko authored
    Commit 64574746 ("vmscan: detect mapped file pages used only once")
    made mapped pages have another round in inactive list because they might
    be just short lived and so we could consider them again next time.  This
    heuristic helps to reduce pressure on the active list with a streaming
    IO worklods.
    
    This patch fixes a regression introduced by this commit for heavy shmem
    based workloads because unlike Anon pages, which are excluded from this
    heuristic because they are usually long lived, shmem pages are handled
    as a regular page cache.
    
    This doesn't work quite well, unfortunately, if the workload is mostly
    backed by shmem (in memory database sitting on 80% of memory) with a
    streaming IO in the background (backup - up to 20% of memory).  Anon
    inactive list is full of (dirty) shmem pages when watermarks are hit.
    Shmem pages are kept in the inactive list (they are referenced) in the
    first round and it is hard to reclaim anything else so we reach lower
    scanning priorities very quickly which leads to an excessive swap out.
    
    Let's fix this by excluding all swap backed pages (they tend to be long
    lived wrt.  the regular page cache anyway) from used-once heuristic and
    rather activate them if they are referenced.
    
    The customer's workload is shmem backed database (80% of RAM) and they
    are measuring transactions/s with an IO in the background (20%).
    Transactions touch more or less random rows in the table.  The
    transaction rate fell by a factor of 3 (in the worst case) because of
    commit 64574746.  This patch restores the previous numbers.
    Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
    Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Reviewed-by: default avatarRik van Riel <riel@redhat.com>
    Cc: <stable@vger.kernel.org>	[2.6.34+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    e4898273
vmscan.c 96 KB