• Vlastimil Babka's avatar
    mm, compaction: simplify deferred compaction · 97d47a65
    Vlastimil Babka authored
    Since commit 53853e2d ("mm, compaction: defer each zone individually
    instead of preferred zone"), compaction is deferred for each zone where
    sync direct compaction fails, and reset where it succeeds.  However, it
    was observed that for DMA zone compaction often appeared to succeed
    while subsequent allocation attempt would not, due to different outcome
    of watermark check.
    
    In order to properly defer compaction in this zone, the candidate zone
    has to be passed back to __alloc_pages_direct_compact() and compaction
    deferred in the zone after the allocation attempt fails.
    
    The large source of mismatch between watermark check in compaction and
    allocation was the lack of alloc_flags and classzone_idx values in
    compaction, which has been fixed in the previous patch.  So with this
    problem fixed, we can simplify the code by removing the candidate_zone
    parameter and deferring in __alloc_pages_direct_compact().
    
    After this patch, the compaction activity during stress-highalloc
    benchmark is still somewhat increased, but it's negligible compared to the
    increase that occurred without the better watermark checking.  This
    suggests that it is still possible to apparently succeed in compaction but
    fail to allocate, possibly due to parallel allocation activity.
    
    [akpm@linux-foundation.org: fix build]
    Suggested-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
    Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Michal Nazarewicz <mina86@mina86.com>
    Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    97d47a65
compaction.c 42.2 KB