mm/compaction: avoid rescanning pageblocks in isolate_freepages
authorVlastimil Babka <vbabka@suse.cz>
Wed, 4 Jun 2014 23:08:34 +0000 (16:08 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 4 Jun 2014 23:54:07 +0000 (16:54 -0700)
commite9ade569910a82614ff5f2c2cea2b65a8d785da4
tree0540262e4eb7d5316e219bd4ef6426649b30b4c4
parentf8c9301fa5a2a8b873c67f2a3d8230d5c13f61b7
mm/compaction: avoid rescanning pageblocks in isolate_freepages

The compaction free scanner in isolate_freepages() currently remembers PFN
of the highest pageblock where it successfully isolates, to be used as the
starting pageblock for the next invocation.  The rationale behind this is
that page migration might return free pages to the allocator when
migration fails and we don't want to skip them if the compaction
continues.

Since migration now returns free pages back to compaction code where they
can be reused, this is no longer a concern.  This patch changes
isolate_freepages() so that the PFN for restarting is updated with each
pageblock where isolation is attempted.  Using stress-highalloc from
mmtests, this resulted in 10% reduction of the pages scanned by the free
scanner.

Note that the somewhat similar functionality that records highest
successful pageblock in zone->compact_cached_free_pfn, remains unchanged.
This cache is used when the whole compaction is restarted, not for
multiple invocations of the free scanner during single compaction.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/compaction.c