path: root/mm/page_alloc.c
diff options
authorMel Gorman <>2009-06-16 15:33:22 -0700
committerLinus Torvalds <>2009-06-16 19:47:45 -0700
commitfa5e084e43eb14c14942027e1e2e894aeed96097 (patch)
tree3e7ebf714858e8dd1de7042fd1ef62294a3ec20f /mm/page_alloc.c
parent90afa5de6f3fa89a733861e843377302479fcf7e (diff)
vmscan: do not unconditionally treat zones that fail zone_reclaim() as full
On NUMA machines, the administrator can configure zone_reclaim_mode that is a more targetted form of direct reclaim. On machines with large NUMA distances for example, a zone_reclaim_mode defaults to 1 meaning that clean unmapped pages will be reclaimed if the zone watermarks are not being met. The problem is that zone_reclaim() failing at all means the zone gets marked full. This can cause situations where a zone is usable, but is being skipped because it has been considered full. Take a situation where a large tmpfs mount is occuping a large percentage of memory overall. The pages do not get cleaned or reclaimed by zone_reclaim(), but the zone gets marked full and the zonelist cache considers them not worth trying in the future. This patch makes zone_reclaim() return more fine-grained information about what occured when zone_reclaim() failued. The zone only gets marked full if it really is unreclaimable. If it's a case that the scan did not occur or if enough pages were not reclaimed with the limited reclaim_mode, then the zone is simply skipped. There is a side-effect to this patch. Currently, if zone_reclaim() successfully reclaimed SWAP_CLUSTER_MAX, an allocation attempt would go ahead. With this patch applied, zone watermarks are rechecked after zone_reclaim() does some work. This bug was introduced by commit 9276b1bc96a132f4068fdee00983c532f43d3a26 ("memory page_alloc zonelist caching speedup") way back in 2.6.19 when the zonelist_cache was introduced. It was not intended that zone_reclaim() aggressively consider the zone to be full when it failed as full direct reclaim can still be an option. Due to the age of the bug, it should be considered a -stable candidate. Signed-off-by: Mel Gorman <> Reviewed-by: Wu Fengguang <> Reviewed-by: Rik van Riel <> Reviewed-by: KOSAKI Motohiro <> Cc: Christoph Lameter <> Cc: <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/page_alloc.c')
1 files changed, 22 insertions, 4 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6407cbfccd7..2f457a756d4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1462,15 +1462,33 @@ zonelist_scan:
if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
unsigned long mark;
+ int ret;
mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
- if (!zone_watermark_ok(zone, order, mark,
- classzone_idx, alloc_flags)) {
- if (!zone_reclaim_mode ||
- !zone_reclaim(zone, gfp_mask, order))
+ if (zone_watermark_ok(zone, order, mark,
+ classzone_idx, alloc_flags))
+ goto try_this_zone;
+ if (zone_reclaim_mode == 0)
+ goto this_zone_full;
+ ret = zone_reclaim(zone, gfp_mask, order);
+ switch (ret) {
+ /* did not scan */
+ goto try_next_zone;
+ /* scanned but unreclaimable */
+ goto this_zone_full;
+ default:
+ /* did we reclaim enough */
+ if (!zone_watermark_ok(zone, order, mark,
+ classzone_idx, alloc_flags))
goto this_zone_full;
page = buffered_rmqueue(preferred_zone, zone, order,
gfp_mask, migratetype);
if (page)