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Commit fa5e084e authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
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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 9276b1bc
("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: default avatarMel Gorman <mel@csn.ul.ie>
Reviewed-by: default avatarWu Fengguang <fengguang.wu@intel.com>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 90afa5de

mm/internal.h

+4 −0
Original line number Diff line number Diff line
@@ -259,4 +259,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
		     unsigned long start, int len, int flags,

		     struct page **pages, struct vm_area_struct **vmas);



#define ZONE_RECLAIM_NOSCAN	-2

#define ZONE_RECLAIM_FULL	-1

#define ZONE_RECLAIM_SOME	0

#define ZONE_RECLAIM_SUCCESS	1

#endif

mm/page_alloc.c

+22 −4
Original line number Diff line number Diff line
@@ -1462,15 +1462,33 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order, 
		BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);

		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))

				goto try_this_zone;



			if (zone_reclaim_mode == 0)

				goto this_zone_full;



			ret = zone_reclaim(zone, gfp_mask, order);

			switch (ret) {

			case ZONE_RECLAIM_NOSCAN:

				/* did not scan */

				goto try_next_zone;

			case ZONE_RECLAIM_FULL:

				/* scanned but unreclaimable */

				goto this_zone_full;

			default:

				/* did we reclaim enough */

				if (!zone_watermark_ok(zone, order, mark,

				    classzone_idx, alloc_flags)) {

				if (!zone_reclaim_mode ||

				    !zone_reclaim(zone, gfp_mask, order))

						classzone_idx, alloc_flags))

					goto this_zone_full;

			}

		}



try_this_zone:

		page = buffered_rmqueue(preferred_zone, zone, order,

						gfp_mask, migratetype);

		if (page)

mm/vmscan.c

+6 −5
Original line number Diff line number Diff line
@@ -2492,16 +2492,16 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 
	 */

	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&

	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)

		return 0;

		return ZONE_RECLAIM_FULL;



	if (zone_is_all_unreclaimable(zone))

		return 0;

		return ZONE_RECLAIM_FULL;



	/*

	 * Do not scan if the allocation should not be delayed.

	 */

	if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))

			return 0;

		return ZONE_RECLAIM_NOSCAN;



	/*

	 * Only run zone reclaim on the local zone or on zones that do not
@@ -2511,10 +2511,11 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 
	 */

	node_id = zone_to_nid(zone);

	if (node_state(node_id, N_CPU) && node_id != numa_node_id())

		return 0;

		return ZONE_RECLAIM_NOSCAN;



	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))

		return 0;

		return ZONE_RECLAIM_NOSCAN;



	ret = __zone_reclaim(zone, gfp_mask, order);

	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);