diff options
authorMel Gorman <mel@csn.ul.ie>2010-09-09 16:38:16 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-09-09 18:57:25 -0700
commit72853e2991a2702ae93aaf889ac7db743a415dd3 (patch)
parent5ee28a447625b9fe64fbf7cff026561084fc5f16 (diff)
mm: page allocator: update free page counters after pages are placed on the free list
When allocating a page, the system uses NR_FREE_PAGES counters to determine if watermarks would remain intact after the allocation was made. This check is made without interrupts disabled or the zone lock held and so is race-prone by nature. Unfortunately, when pages are being freed in batch, the counters are updated before the pages are added on the list. During this window, the counters are misleading as the pages do not exist yet. When under significant pressure on systems with large numbers of CPUs, it's possible for processes to make progress even though they should have been stalled. This is particularly problematic if a number of the processes are using GFP_ATOMIC as the min watermark can be accidentally breached and in extreme cases, the system can livelock. This patch updates the counters after the pages have been added to the list. This makes the allocator more cautious with respect to preserving the watermarks and mitigates livelock possibilities. [akpm@linux-foundation.org: avoid modifying incoming args] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reviewed-by: Rik van Riel <riel@redhat.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Reviewed-by: Christoph Lameter <cl@linux.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 5 insertions, 4 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a9649f4b261e..452e2ba06c7c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -588,13 +588,13 @@ static void free_pcppages_bulk(struct zone *zone, int count,
int migratetype = 0;
int batch_free = 0;
+ int to_free = count;
zone->all_unreclaimable = 0;
zone->pages_scanned = 0;
- __mod_zone_page_state(zone, NR_FREE_PAGES, count);
- while (count) {
+ while (to_free) {
struct page *page;
struct list_head *list;
@@ -619,8 +619,9 @@ static void free_pcppages_bulk(struct zone *zone, int count,
__free_one_page(page, zone, 0, page_private(page));
trace_mm_page_pcpu_drain(page, 0, page_private(page));
- } while (--count && --batch_free && !list_empty(list));
+ } while (--to_free && --batch_free && !list_empty(list));
+ __mod_zone_page_state(zone, NR_FREE_PAGES, count);
@@ -631,8 +632,8 @@ static void free_one_page(struct zone *zone, struct page *page, int order,
zone->all_unreclaimable = 0;
zone->pages_scanned = 0;
- __mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);
__free_one_page(page, zone, order, migratetype);
+ __mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);

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