path: root/mm/page_isolation.c
diff options
authorMinchan Kim <minchan@kernel.org>2012-07-31 16:43:56 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-31 18:42:45 -0700
commit702d1a6e0766d45642c934444fd41f658d251305 (patch)
tree6c9144521b03f11f7ea2e709f066b90a9b9f38d5 /mm/page_isolation.c
parent2cfed0752808625d30aca7fc9f383af386fd8a13 (diff)
memory-hotplug: fix kswapd looping forever problem
When hotplug offlining happens on zone A, it starts to mark freed page as MIGRATE_ISOLATE type in buddy for preventing further allocation. (MIGRATE_ISOLATE is very irony type because it's apparently on buddy but we can't allocate them). When the memory shortage happens during hotplug offlining, current task starts to reclaim, then wake up kswapd. Kswapd checks watermark, then go sleep because current zone_watermark_ok_safe doesn't consider MIGRATE_ISOLATE freed page count. Current task continue to reclaim in direct reclaim path without kswapd's helping. The problem is that zone->all_unreclaimable is set by only kswapd so that current task would be looping forever like below. __alloc_pages_slowpath restart: wake_all_kswapd rebalance: __alloc_pages_direct_reclaim do_try_to_free_pages if global_reclaim && !all_unreclaimable return 1; /* It means we did did_some_progress */ skip __alloc_pages_may_oom should_alloc_retry goto rebalance; If we apply KOSAKI's patch[1] which doesn't depends on kswapd about setting zone->all_unreclaimable, we can solve this problem by killing some task in direct reclaim path. But it doesn't wake up kswapd, still. It could be a problem still if other subsystem needs GFP_ATOMIC request. So kswapd should consider MIGRATE_ISOLATE when it calculate free pages BEFORE going sleep. This patch counts the number of MIGRATE_ISOLATE page block and zone_watermark_ok_safe will consider it if the system has such blocks (fortunately, it's very rare so no problem in POV overhead and kswapd is never hotpath). Copy/modify from Mel's quote " Ideal solution would be "allocating" the pageblock. It would keep the free space accounting as it is but historically, memory hotplug didn't allocate pages because it would be difficult to detect if a pageblock was isolated or if part of some balloon. Allocating just full pageblocks would work around this, However, it would play very badly with CMA. " [1] http://lkml.org/lkml/2012/6/14/74 [akpm@linux-foundation.org: simplify nr_zone_isolate_freepages(), rework zone_watermark_ok_safe() comment, simplify set_pageblock_isolate() and restore_pageblock_isolate()] [akpm@linux-foundation.org: fix CONFIG_MEMORY_ISOLATION=n build] Signed-off-by: Minchan Kim <minchan@kernel.org> Suggested-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Tested-by: Aaditya Kumar <aaditya.kumar.30@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page_isolation.c')
1 files changed, 24 insertions, 2 deletions
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index fb482cf438d..247d1f17573 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -8,6 +8,28 @@
#include <linux/memory.h>
#include "internal.h"
+/* called while holding zone->lock */
+static void set_pageblock_isolate(struct page *page)
+ if (get_pageblock_migratetype(page) == MIGRATE_ISOLATE)
+ return;
+ set_pageblock_migratetype(page, MIGRATE_ISOLATE);
+ page_zone(page)->nr_pageblock_isolate++;
+/* called while holding zone->lock */
+static void restore_pageblock_isolate(struct page *page, int migratetype)
+ struct zone *zone = page_zone(page);
+ if (WARN_ON(get_pageblock_migratetype(page) != MIGRATE_ISOLATE))
+ return;
+ BUG_ON(zone->nr_pageblock_isolate <= 0);
+ set_pageblock_migratetype(page, migratetype);
+ zone->nr_pageblock_isolate--;
int set_migratetype_isolate(struct page *page)
struct zone *zone;
@@ -54,7 +76,7 @@ int set_migratetype_isolate(struct page *page)
if (!ret) {
- set_pageblock_migratetype(page, MIGRATE_ISOLATE);
+ set_pageblock_isolate(page);
move_freepages_block(zone, page, MIGRATE_ISOLATE);
@@ -72,8 +94,8 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype)
spin_lock_irqsave(&zone->lock, flags);
if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
goto out;
- set_pageblock_migratetype(page, migratetype);
move_freepages_block(zone, page, migratetype);
+ restore_pageblock_isolate(page, migratetype);
spin_unlock_irqrestore(&zone->lock, flags);