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authorJohannes Weiner <hannes@cmpxchg.org>2014-10-02 16:21:10 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-14 09:00:13 -0800
commit6619741f17f541113a02c30f22a9ca22e32c9546 (patch)
treef81831985190647ac56111322985e4e66db6b9ff
parent7adcd472679503b219029dea246a85db415b8c65 (diff)
mm: page_alloc: fix zone allocation fairness on UP
commit abe5f972912d086c080be4bde67750630b6fb38b upstream. The zone allocation batches can easily underflow due to higher-order allocations or spills to remote nodes. On SMP that's fine, because underflows are expected from concurrency and dealt with by returning 0. But on UP, zone_page_state will just return a wrapped unsigned long, which will get past the <= 0 check and then consider the zone eligible until its watermarks are hit. Commit 3a025760fc15 ("mm: page_alloc: spill to remote nodes before waking kswapd") already made the counter-resetting use atomic_long_read() to accomodate underflows from remote spills, but it didn't go all the way with it. Make it clear that these batches are expected to go negative regardless of concurrency, and use atomic_long_read() everywhere. Fixes: 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy") Reported-by: Vlastimil Babka <vbabka@suse.cz> Reported-by: Leon Romanovsky <leon@leon.nu> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Mel Gorman <mgorman@suse.de> Cc: <stable@vger.kernel.org> [3.12+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--mm/page_alloc.c7
1 files changed, 3 insertions, 4 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 586f58685e25..7b2611a055a7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1957,7 +1957,7 @@ zonelist_scan:
if (alloc_flags & ALLOC_FAIR) {
if (!zone_local(preferred_zone, zone))
continue;
- if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0)
+ if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0)
continue;
}
/*
@@ -5670,9 +5670,8 @@ static void __setup_per_zone_wmarks(void)
zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp >> 1);
__mod_zone_page_state(zone, NR_ALLOC_BATCH,
- high_wmark_pages(zone) -
- low_wmark_pages(zone) -
- zone_page_state(zone, NR_ALLOC_BATCH));
+ high_wmark_pages(zone) - low_wmark_pages(zone) -
+ atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));
setup_zone_migrate_reserve(zone);
spin_unlock_irqrestore(&zone->lock, flags);