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    SubjectRe: [PATCH] mm: consider all swapped back pages in used-once logic
    On 05/17/2012 05:13 AM, Michal Hocko wrote:
    > [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.
    >
    > CC: Johannes Weiner<hannes@cmpxchg.org>
    > CC: Andrew Morton<akpm@linux-foundation.org>
    > CC: Mel Gorman<mel@csn.ul.ie>
    > CC: Minchan Kim<minchan@kernel.org>
    > CC: KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com>
    > CC: Rik van Riel<riel@redhat.com>
    > CC: stable [2.6.34+]
    > Signed-off-by: Michal Hocko<mhocko@suse.cz>

    Reviewed-by: Rik van Riel <riel@redhat.com>

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