| From 4746efded84d7c5a9c8d64d4c6e814ff0cf9fb42 Mon Sep 17 00:00:00 2001 |
| From: Shaohua Li <shaohua.li@intel.com> |
| Date: Tue, 19 Jul 2011 08:49:26 -0700 |
| Subject: vmscan: fix a livelock in kswapd |
| |
| From: Shaohua Li <shaohua.li@intel.com> |
| |
| commit 4746efded84d7c5a9c8d64d4c6e814ff0cf9fb42 upstream. |
| |
| 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> |
| 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@suse.de> |
| |
| --- |
| mm/vmscan.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| --- a/mm/vmscan.c |
| +++ b/mm/vmscan.c |
| @@ -2245,7 +2245,8 @@ 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? */ |