• Michal Hocko's avatar
    mm: throttle on IO only when there are too many dirty and writeback pages · ede37713
    Michal Hocko authored
    wait_iff_congested has been used to throttle allocator before it retried
    another round of direct reclaim to allow the writeback to make some
    progress and prevent reclaim from looping over dirty/writeback pages
    without making any progress.
    We used to do congestion_wait before commit 0e093d99 ("writeback: do
    not sleep on the congestion queue if there are no congested BDIs or if
    significant congestion is not being encountered in the current zone")
    but that led to undesirable stalls and sleeping for the full timeout
    even when the BDI wasn't congested.  Hence wait_iff_congested was used
    But it seems that even wait_iff_congested doesn't work as expected.  We
    might have a small file LRU list with all pages dirty/writeback and yet
    the bdi is not congested so this is just a cond_resched in the end and
    can end up triggering pre mature OOM.
    This patch replaces the unconditional wait_iff_congested by
    congestion_wait which is executed only if we _know_ that the last round
    of direct reclaim didn't make any progress and dirty+writeback pages are
    more than a half of the reclaimable pages on the zone which might be
    usable for our target allocation.  This shouldn't reintroduce stalls
    fixed by 0e093d99 because congestion_wait is called only when we are
    getting hopeless when sleeping is a better choice than OOM with many
    pages under IO.
    We have to preserve logic introduced by commit 373ccbe5 ("mm,
    vmstat: allow WQ concurrency to discover memory reclaim doesn't make any
    progress") into the __alloc_pages_slowpath now that wait_iff_congested
    is not used anymore.  As the only remaining user of wait_iff_congested
    is shrink_inactive_list we can remove the WQ specific short sleep from
    wait_iff_congested because the sleep is needed to be done only once in
    the allocation retry cycle.
    [mhocko@suse.com: high_zoneidx->ac_classzone_idx to evaluate memory reserves properly]
     Link: http://lkml.kernel.org/r/1463051677-29418-2-git-send-email-mhocko@kernel.orgSigned-off-by: default avatarMichal Hocko <mhocko@suse.com>
    Acked-by: default avatarHillf Danton <hillf.zj@alibaba-inc.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Joonsoo Kim <js1304@gmail.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
backing-dev.c 25.9 KB