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    Subject[PATCH 10/11] mm: vmscan: Check if reclaim should really abort even if compaction_ready() is true for one zone
    Date
    If compaction can proceed for a given zone, shrink_zones() does not
    reclaim any more pages from it. After commit [e0c2327: vmscan: abort
    reclaim/compaction if compaction can proceed], do_try_to_free_pages()
    tries to finish as soon as possible once one zone can compact.

    This was intended to prevent slabs being shrunk unnecessarily but
    there are side-effects. One is that a small zone that is ready for
    compaction will abort reclaim even if the chances of successfully
    allocating a THP from that zone is small. It also means that reclaim
    can return too early even though sc->nr_to_reclaim pages were not
    reclaimed.

    This partially reverts the commit until it is proven that slabs are
    really being shrunk unnecessarily but preserves the check to return
    1 to avoid OOM if reclaim was aborted prematurely.

    [aarcange@redhat.com: This patch replaces a revert from Andrea]
    Signed-off-by: Mel Gorman <mgorman@suse.de>
    ---
    mm/vmscan.c | 19 +++++++++----------
    1 files changed, 9 insertions(+), 10 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index d497248..298ceb8 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2176,7 +2176,8 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
    *
    * This function returns true if a zone is being reclaimed for a costly
    * high-order allocation and compaction is ready to begin. This indicates to
    - * the caller that it should retry the allocation or fail.
    + * the caller that it should consider retrying the allocation instead of
    + * further reclaim.
    */
    static bool shrink_zones(int priority, struct zonelist *zonelist,
    struct scan_control *sc)
    @@ -2185,7 +2186,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
    struct zone *zone;
    unsigned long nr_soft_reclaimed;
    unsigned long nr_soft_scanned;
    - bool should_abort_reclaim = false;
    + bool aborted_reclaim = false;

    for_each_zone_zonelist_nodemask(zone, z, zonelist,
    gfp_zone(sc->gfp_mask), sc->nodemask) {
    @@ -2211,7 +2212,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
    * allocations.
    */
    if (compaction_ready(zone, sc)) {
    - should_abort_reclaim = true;
    + aborted_reclaim = true;
    continue;
    }
    }
    @@ -2233,7 +2234,7 @@ static bool shrink_zones(int priority, struct zonelist *zonelist,
    shrink_zone(priority, zone, sc);
    }

    - return should_abort_reclaim;
    + return aborted_reclaim;
    }

    static bool zone_reclaimable(struct zone *zone)
    @@ -2287,7 +2288,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    struct zoneref *z;
    struct zone *zone;
    unsigned long writeback_threshold;
    - bool should_abort_reclaim;
    + bool aborted_reclaim;

    get_mems_allowed();
    delayacct_freepages_start();
    @@ -2299,9 +2300,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    sc->nr_scanned = 0;
    if (!priority)
    disable_swap_token(sc->mem_cgroup);
    - should_abort_reclaim = shrink_zones(priority, zonelist, sc);
    - if (should_abort_reclaim)
    - break;
    + aborted_reclaim = shrink_zones(priority, zonelist, sc);

    /*
    * Don't shrink slabs when reclaiming memory from
    @@ -2368,8 +2367,8 @@ out:
    if (oom_killer_disabled)
    return 0;

    - /* Aborting reclaim to try compaction? don't OOM, then */
    - if (should_abort_reclaim)
    + /* Aborted reclaim to try compaction? don't OOM, then */
    + if (aborted_reclaim)
    return 1;

    /* top priority shrink_zones still had more to do? don't OOM, then */
    --
    1.7.3.4


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