linux-kernel - [PATCH 3.19 041/177] mm: fix negative nr

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Date:	Mon, 16 Mar 2015 15:07:28 +0100
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.19 041/177] mm: fix negative nr_isolated counts

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hugh Dickins <hughd@...gle.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@...gle.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@....com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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

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