• David Rientjes's avatar
    mm, compaction: abort free scanner if split fails · a4f04f2c
    David Rientjes authored
    If the memory compaction free scanner cannot successfully split a free
    page (only possible due to per-zone low watermark), terminate the free
    scanner rather than continuing to scan memory needlessly.  If the
    watermark is insufficient for a free page of order <= cc->order, then
    terminate the scanner since all future splits will also likely fail.
    This prevents the compaction freeing scanner from scanning all memory on
    very large zones (very noticeable for zones > 128GB, for instance) when
    all splits will likely fail while holding zone->lock.
    compaction_alloc() iterating a 128GB zone has been benchmarked to take
    over 400ms on some systems whereas any free page isolated and ready to
    be split ends up failing in split_free_page() because of the low
    watermark check and thus the iteration continues.
    The next time compaction occurs, the freeing scanner will likely start
    at the end of the zone again since no success was made previously and we
    get the same lengthy iteration until the zone is brought above the low
    watermark.  All thp page faults can take >400ms in such a state without
    this fix.
    Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1606211820350.97086@chino.kir.corp.google.comSigned-off-by: default avatarDavid Rientjes <rientjes@google.com>
    Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Mel Gorman <mgorman@techsingularity.net>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
compaction.c 56.4 KB