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Subject[ 31/40] mm: vmscan: check if reclaim should really abort even if compaction_ready() is true for one zone
From: Greg KH <>

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


From: Mel Gorman <>

commit 0cee34fd72c582b4f8ad8ce00645b75fb4168199 upstream.

Stable note: Not tracked on Bugzilla. THP and compaction was found to
aggressively reclaim pages and stall systems under different
situations that was addressed piecemeal over time.

If compaction can proceed for a given zone, shrink_zones() does not
reclaim any more pages from it. After commit [e0c2327: vmscan: abort
reclaim/compaction if compaction can proceed], do_try_to_free_pages()
tries to finish as soon as possible once one zone can compact.

This was intended to prevent slabs being shrunk unnecessarily but there
are side-effects. One is that a small zone that is ready for compaction
will abort reclaim even if the chances of successfully allocating a THP
from that zone is small. It also means that reclaim can return too early
even though sc->nr_to_reclaim pages were not reclaimed.

This partially reverts the commit until it is proven that slabs are really
being shrunk unnecessarily but preserves the check to return 1 to avoid
OOM if reclaim was aborted prematurely.

[ This patch replaces a revert from Andrea]
Signed-off-by: Mel Gorman <>
Reviewed-by: Rik van Riel <>
Cc: Andrea Arcangeli <>
Cc: Minchan Kim <>
Cc: Dave Jones <>
Cc: Jan Kara <>
Cc: Andy Isaacson <>
Cc: Nai Xia <>
Cc: Johannes Weiner <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Mel Gorman <>
Signed-off-by: Greg Kroah-Hartman <>

mm/vmscan.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2129,7 +2129,8 @@ static inline bool compaction_ready(stru
* This function returns true if a zone is being reclaimed for a costly
* high-order allocation and compaction is ready to begin. This indicates to
- * the caller that it should retry the allocation or fail.
+ * the caller that it should consider retrying the allocation instead of
+ * further reclaim.
static bool shrink_zones(int priority, struct zonelist *zonelist,
struct scan_control *sc)
@@ -2138,7 +2139,7 @@ static bool shrink_zones(int priority, s
struct zone *zone;
unsigned long nr_soft_reclaimed;
unsigned long nr_soft_scanned;
- bool should_abort_reclaim = false;
+ bool aborted_reclaim = false;

for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -2164,7 +2165,7 @@ static bool shrink_zones(int priority, s
* allocations.
if (compaction_ready(zone, sc)) {
- should_abort_reclaim = true;
+ aborted_reclaim = true;
@@ -2186,7 +2187,7 @@ static bool shrink_zones(int priority, s
shrink_zone(priority, zone, sc);

- return should_abort_reclaim;
+ return aborted_reclaim;

static bool zone_reclaimable(struct zone *zone)
@@ -2240,7 +2241,7 @@ static unsigned long do_try_to_free_page
struct zoneref *z;
struct zone *zone;
unsigned long writeback_threshold;
- bool should_abort_reclaim;
+ bool aborted_reclaim;

@@ -2252,9 +2253,7 @@ static unsigned long do_try_to_free_page
sc->nr_scanned = 0;
if (!priority)
- should_abort_reclaim = shrink_zones(priority, zonelist, sc);
- if (should_abort_reclaim)
- break;
+ aborted_reclaim = shrink_zones(priority, zonelist, sc);

* Don't shrink slabs when reclaiming memory from
@@ -2320,8 +2319,8 @@ out:
if (oom_killer_disabled)
return 0;

- /* Aborting reclaim to try compaction? don't OOM, then */
- if (should_abort_reclaim)
+ /* Aborted reclaim to try compaction? don't OOM, then */
+ if (aborted_reclaim)
return 1;

/* top priority shrink_zones still had more to do? don't OOM, then */

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