From: Shaohua Li Date: Tue, 19 Jul 2011 15:49:26 +0000 (-0700) Subject: vmscan: fix a livelock in kswapd X-Git-Url: http://git.alex.org.uk vmscan: fix a livelock in kswapd BugLink: http://bugs.launchpad.net/bugs/813797 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 Acked-by: Mel Gorman Cc: Minchan Kim Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Acked-by: Andy Whitcroft Acked-by: Stefan Bader Signed-off-by: Tim Gardner --- diff --git a/mm/vmscan.c b/mm/vmscan.c index 4b8b37c..1e0eefe 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2245,7 +2245,8 @@ 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? */