[PATCH 3.19 041/177] mm: fix negative nr_isolated counts

Greg Kroah-Hartman
2015-03-16T15:56:47Z

From: Hugh Dickins <hughd@google.com>

commit ff59909a077b3c51c168cb658601c6b63136a347 upstream.

The vmstat interfaces are good at hiding negative counts (at least when
CONFIG_SMP); but if you peer behind the curtain, you find that
nr_isolated_anon and nr_isolated_file soon go negative, and grow ever
more negative: so they can absorb larger and larger numbers of isolated
pages, yet still appear to be zero.

I'm happy to avoid a congestion_wait() when too_many_isolated() myself;
but I guess it's there for a good reason, in which case we ought to get
too_many_isolated() working again.

The imbalance comes from isolate_migratepages()'s ISOLATE_ABORT case:
putback_movable_pages() decrements the NR_ISOLATED counts, but we forgot
to call acct_isolated() to increment them.

It is possible that the bug whcih this patch fixes could cause OOM kills
when the system still has a lot of reclaimable page cache.

Fixes: edc2ca612496 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/compaction.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1015,8 +1015,10 @@ static isolate_migrate_t isolate_migrate
low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn,
isolate_mode);

- if (!low_pfn || cc->contended)
+ if (!low_pfn || cc->contended) {
+ acct_isolated(zone, cc);
return ISOLATE_ABORT;
+ }

/*
* Either we isolated something and proceed with migration. Or