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authorShaohua Li <shaohua.li@intel.com>2011-07-19 08:49:26 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-07-19 22:09:31 -0700
commit4746efded84d7c5a9c8d64d4c6e814ff0cf9fb42 (patch)
tree174f400db27c1a1d9a66407931199aabfdce6bba
parentf7b88631a89757d70192044c9d9f2e8d2fc02f2c (diff)
vmscan: fix a livelock in kswapd
I'm running a workload which triggers a lot of swap in a machine with 4 nodes. After I kill the workload, I found a kswapd livelock. Sometimes kswapd3 or kswapd2 are keeping running and I can't access filesystem, but most memory is free. This looks like a regression since commit 08951e545918c159 ("mm: vmscan: correct check for kswapd sleeping in sleeping_prematurely"). Node 2 and 3 have only ZONE_NORMAL, but balance_pgdat() will return 0 for classzone_idx. The reason is end_zone in balance_pgdat() is 0 by default, if all zones have watermark ok, end_zone will keep 0. Later sleeping_prematurely() always returns true. Because this is an order 3 wakeup, and if classzone_idx is 0, both balanced_pages and present_pages in pgdat_balanced() are 0. We add a special case here. If a zone has no page, we think it's balanced. This fixes the livelock. Signed-off-by: Shaohua Li <shaohua.li@intel.com> Acked-by: Mel Gorman <mgorman@suse.de> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/vmscan.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5ed24b94c5e..d036e59d302 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2310,7 +2310,8 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
for (i = 0; i <= classzone_idx; i++)
present_pages += pgdat->node_zones[i].present_pages;
- return balanced_pages > (present_pages >> 2);
+ /* A special case here: if zone has no page, we think it's balanced */
+ return balanced_pages >= (present_pages >> 2);
}
/* is kswapd sleeping prematurely? */