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Vlastimil Babka authored
The migrate scanner in async compaction is currently limited to MIGRATE_MOVABLE pageblocks. This is a heuristic intended to reduce latency, based on the assumption that non-MOVABLE pageblocks are unlikely to contain movable pages. However, with the exception of THP's, most high-order allocations are not movable. Should the async compaction succeed, this increases the chance that the non-MOVABLE allocations will fallback to a MOVABLE pageblock, making the long-term fragmentation worse. This patch attempts to help the situation by changing async direct compaction so that the migrate scanner only scans the pageblocks of the requested migratetype. If it's a non-MOVABLE type and there are such pageblocks that do contain movable pages, chances are that the allocation can succeed within one of such pageblocks, removing the need for a fallback. If that fails, the subsequent sync attempt will ignore this restriction. In testing based on 4.9 kernel with stress-highalloc from mmtests configured for order-4 GFP_KERNEL allocations, this patch has reduced the number of unmovable allocations falling back to movable pageblocks by 30%. The number of movable allocations falling back is reduced by 12%. Link: http://lkml.kernel.org/r/20170307131545.28577-8-vbabka@suse.czSigned-off-by:
Vlastimil Babka <vbabka@suse.cz> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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