Commit 14af4a5e authored May 05, 2016 by Hugh Dickins Committed by Linus Torvalds May 05, 2016

mm, cma: prevent nr_isolated_* counters from going negative



/proc/sys/vm/stat_refresh warns nr_isolated_anon and nr_isolated_file go
increasingly negative under compaction: which would add delay when
should be none, or no delay when should delay.  The bug in compaction
was due to a recent mmotm patch, but much older instance of the bug was
also noticed in isolate_migratepages_range() which is used for CMA and
gigantic hugepage allocations.

The bug is caused by putback_movable_pages() in an error path
decrementing the isolated counters without them being previously
incremented by acct_isolated().  Fix isolate_migratepages_range() by
removing the error-path putback, thus reaching acct_isolated() with
migratepages still isolated, and leaving putback to caller like most
other places do.

Fixes: edc2ca61 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
[vbabka@suse.cz: expanded the changelog]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bc22af74

mm/compaction.c

+1 −9

Original line number	Diff line number	Diff line
		@@ -852,16 +852,8 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
		pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
		ISOLATE_UNEVICTABLE);

		/*
		* In case of fatal failure, release everything that might
		* have been isolated in the previous iteration, and signal
		* the failure back to caller.
		*/
		if (!pfn) {
		putback_movable_pages(&cc->migratepages);
		cc->nr_migratepages = 0;
		if (!pfn)
		break;
		}

		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
		break;