From: Shaohua Li <[email protected]>
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 <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/vmscan.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN mm/vmscan.c~vmscan-fix-a-livelock-in-kswapd mm/vmscan.c
--- a/mm/vmscan.c~vmscan-fix-a-livelock-in-kswapd
+++ a/mm/vmscan.c
@@ -2310,7 +2310,8 @@ static bool pgdat_balanced(pg_data_t *pg
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? */
_
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