mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode
At present MIGRATE_SYNC_LIGHT is allowing __isolate_lru_page() to isolate a PageWriteback page, which __unmap_and_move() then rejects with -EBUSY: of course the writeback might complete in between, but that's not what we usually expect, so probably better not to isolate it. When tested by stress-highalloc from mmtests, this has reduced the number of page migrate failures by 60-70%. Link: http://lkml.kernel.org/r/20160721073614.24395-2-vbabka@suse.czSigned-off-by: NHugh Dickins <hughd@google.com> Signed-off-by: NVlastimil Babka <vbabka@suse.cz> Acked-by: NMichal Hocko <mhocko@suse.com> Acked-by: NMel Gorman <mgorman@techsingularity.net> Acked-by: NDavid Rientjes <rientjes@google.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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