[PATCH 04/11] mm: vmscan: Do not OOM if aborting reclaim to start compaction

[Mel Gorman <mgorman@suse.de>]

During direct reclaim it is possible that reclaim will be aborted so
that compaction can be attempted to satisfy a high-order allocation. If
this decision is made before any pages are reclaimed, it is possible
that 0 is returned to the page allocator potentially triggering an
OOM. This has not been observed but it is a possibility so this patch
addresses it.

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 mm/vmscan.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index faf88b8..69057b5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2222,6 +2222,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 	struct zoneref *z;
 	struct zone *zone;
 	unsigned long writeback_threshold;
+	bool should_abort_reclaim;
 
 	get_mems_allowed();
 	delayacct_freepages_start();
@@ -2233,7 +2234,8 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 		sc->nr_scanned = 0;
 		if (!priority)
 			disable_swap_token(sc->mem_cgroup);
-		if (shrink_zones(priority, zonelist, sc))
+		should_abort_reclaim = shrink_zones(priority, zonelist, sc);
+		if (should_abort_reclaim)
 			break;
 
 		/*
@@ -2301,6 +2303,10 @@ out:
 	if (oom_killer_disabled)
 		return 0;
 
+	/* Aborting reclaim to try compaction? don't OOM, then */
+	if (should_abort_reclaim)
+		return 1;
+
 	/* top priority shrink_zones still had more to do? don't OOM, then */
 	if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
 		return 1;
-- 
1.7.3.4