On 06/11/2012 07:33 PM, KOSAKI Motohiro wrote:
On Mon, Apr 23, 2012 at 4:56 PM, Ying Han<yinghan@xxxxxxxxxx> wrote:This is not a patch targeted to be merged at all, but trying to understand a logic in global direct reclaim. There is a logic in global direct reclaim where reclaim fails on priority 0 and zone->all_unreclaimable is not set, it will cause the direct to start over from DEF_PRIORITY. In some extreme cases, we've seen the system hang which is very likely caused by direct reclaim enters infinite loop. There have been serious patches trying to fix similar issue and the latest patch has good summary of all the efforts: commit 929bea7c714220fc76ce3f75bef9056477c28e74 Author: KOSAKI Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx> Date: Thu Apr 14 15:22:12 2011 -0700 vmscan: all_unreclaimable() use zone->all_unreclaimable as a name Kosaki explained the problem triggered by async zone->all_unreclaimable and zone->pages_scanned where the later one was being checked by direct reclaim. However, after the patch, the problem remains where the setting of zone->all_unreclaimable is asynchronous with zone is actually reclaimable or not. The zone->all_unreclaimable flag is set by kswapd by checking zone->pages_scanned in zone_reclaimable(). Is that possible to have zone->all_unreclaimable == false while the zone is actually unreclaimable?I'm backed very old threads. :-( I could reproduce this issue by using memory hotplug. Can anyone review following patch?
Looks like a sane approach to me.
Reported-by: Aaditya Kumar<aaditya.kumar.30@xxxxxxxxx> Reported-by: Ying Han<yinghan@xxxxxxxxxx> Cc: Nick Piggin<npiggin@xxxxxxxxx> Cc: Rik van Riel<riel@xxxxxxxxxx> Cc: Michal Hocko<mhocko@xxxxxxx> Cc: Johannes Weiner<hannes@xxxxxxxxxxx> Cc: Mel Gorman<mel@xxxxxxxxx> Cc: KAMEZAWA Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx> Cc: Minchan Kim<minchan.kim@xxxxxxxxx> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx>
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