• Mel Gorman's avatar
    mm, vmstat: remove zone and node double accounting by approximating retries · bca67592
    Mel Gorman authored
    The number of LRU pages, dirty pages and writeback pages must be
    accounted for on both zones and nodes because of the reclaim retry
    logic, compaction retry logic and highmem calculations all depending on
    per-zone stats.
    
    Many lowmem allocations are immune from OOM kill due to a check in
    __alloc_pages_may_oom for (ac->high_zoneidx < ZONE_NORMAL) since commit
    03668b3c ("oom: avoid oom killer for lowmem allocations").  The
    exception is costly high-order allocations or allocations that cannot
    fail.  If the __alloc_pages_may_oom avoids OOM-kill for low-order lowmem
    allocations then it would fall through to __alloc_pages_direct_compact.
    
    This patch will blindly retry reclaim for zone-constrained allocations
    in should_reclaim_retry up to MAX_RECLAIM_RETRIES.  This is not ideal
    but without per-zone stats there are not many alternatives.  The impact
    it that zone-constrained allocations may delay before considering the
    OOM killer.
    
    As there is no guarantee enough memory can ever be freed to satisfy
    compaction, this patch avoids retrying compaction for zone-contrained
    allocations.
    
    In combination, that means that the per-node stats can be used when
    deciding whether to continue reclaim using a rough approximation.  While
    it is possible this will make the wrong decision on occasion, it will
    not infinite loop as the number of reclaim attempts is capped by
    MAX_RECLAIM_RETRIES.
    
    The final step is calculating the number of dirtyable highmem pages.  As
    those calculations only care about the global count of file pages in
    highmem.  This patch uses a global counter used instead of per-zone
    stats as it is sufficient.
    
    In combination, this allows the per-zone LRU and dirty state counters to
    be removed.
    
    [mgorman@techsingularity.net: fix acct_highmem_file_pages()]
      Link: http://lkml.kernel.org/r/1468853426-12858-4-git-send-email-mgorman@techsingularity.netLink: http://lkml.kernel.org/r/1467970510-21195-35-git-send-email-mgorman@techsingularity.netSigned-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
    Suggested by: Michal Hocko <mhocko@kernel.org>
    Acked-by: default avatarHillf Danton <hillf.zj@alibaba-inc.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Rik van Riel <riel@surriel.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>
    bca67592
compaction.c 58.1 KB