From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 0F5046B009E for ; Fri, 21 Aug 2009 11:41:07 -0400 (EDT) Date: Fri, 21 Aug 2009 09:46:28 +0800 From: Wu Fengguang Subject: Re: [PATCH -v2] mm: do batched scans for mem_cgroup Message-ID: <20090821014628.GA31483@localhost> References: <20090820024929.GA19793@localhost> <20090820121347.8a886e4b.kamezawa.hiroyu@jp.fujitsu.com> <20090820040533.GA27540@localhost> <20090820051656.GB26265@balbir.in.ibm.com> <20090821013926.GA30823@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090821013926.GA30823@localhost> Sender: owner-linux-mm@kvack.org To: Balbir Singh Cc: KAMEZAWA Hiroyuki , Andrew Morton , KOSAKI Motohiro , Rik van Riel , Johannes Weiner , Avi Kivity , Andrea Arcangeli , "Dike, Jeffrey G" , Hugh Dickins , Christoph Lameter , Mel Gorman , LKML , linux-mm , "nishimura@mxp.nes.nec.co.jp" , "lizf@cn.fujitsu.com" , "menage@google.com" List-ID: On Fri, Aug 21, 2009 at 09:39:26AM +0800, Wu Fengguang wrote: > On Thu, Aug 20, 2009 at 01:16:56PM +0800, Balbir Singh wrote: > > * Wu Fengguang [2009-08-20 12:05:33]: > > > > > On Thu, Aug 20, 2009 at 11:13:47AM +0800, KAMEZAWA Hiroyuki wrote: > > > > On Thu, 20 Aug 2009 10:49:29 +0800 > > > > Wu Fengguang wrote: > > > > > > > > > For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, > > > > > in which case shrink_list() _still_ calls isolate_pages() with the much > > > > > larger SWAP_CLUSTER_MAX. It effectively scales up the inactive list > > > > > scan rate by up to 32 times. > > > > > > > > > > For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4. > > > > > So when shrink_zone() expects to scan 4 pages in the active/inactive > > > > > list, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect. > > > > > > > > > > The accesses to nr_saved_scan are not lock protected and so not 100% > > > > > accurate, however we can tolerate small errors and the resulted small > > > > > imbalanced scan rates between zones. > > > > > > > > > > This batching won't blur up the cgroup limits, since it is driven by > > > > > "pages reclaimed" rather than "pages scanned". When shrink_zone() > > > > > decides to cancel (and save) one smallish scan, it may well be called > > > > > again to accumulate up nr_saved_scan. > > > > > > > > > > It could possibly be a problem for some tiny mem_cgroup (which may be > > > > > _full_ scanned too much times in order to accumulate up nr_saved_scan). > > > > > > > > > > CC: Rik van Riel > > > > > CC: Minchan Kim > > > > > CC: Balbir Singh > > > > > CC: KOSAKI Motohiro > > > > > CC: KAMEZAWA Hiroyuki > > > > > Signed-off-by: Wu Fengguang > > > > > --- > > > > > > > > Hmm, how about this ? > > > > == > > > > Now, nr_saved_scan is tied to zone's LRU. > > > > But, considering how vmscan works, it should be tied to reclaim_stat. > > > > > > > > By this, memcg can make use of nr_saved_scan information seamlessly. > > > > > > Good idea, full patch updated with your signed-off-by :) > > > > > > Thanks, > > > Fengguang > > > --- > > > mm: do batched scans for mem_cgroup > > > > > > For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, > > > in which case shrink_list() _still_ calls isolate_pages() with the much > > > larger SWAP_CLUSTER_MAX. It effectively scales up the inactive list > > > scan rate by up to 32 times. > > > > > > For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4. > > > So when shrink_zone() expects to scan 4 pages in the active/inactive > > > list, it will be scanned SWAP_CLUSTER_MAX=32 pages in effect. > > > > > > The accesses to nr_saved_scan are not lock protected and so not 100% > > > accurate, however we can tolerate small errors and the resulted small > > > imbalanced scan rates between zones. > > > > > > This batching won't blur up the cgroup limits, since it is driven by > > > "pages reclaimed" rather than "pages scanned". When shrink_zone() > > > decides to cancel (and save) one smallish scan, it may well be called > > > again to accumulate up nr_saved_scan. > > > > > > It could possibly be a problem for some tiny mem_cgroup (which may be > > > _full_ scanned too much times in order to accumulate up nr_saved_scan). > > > > > > > Looks good to me, how did you test it? > > I observed the shrink_inactive_list() calls with this patch: > > @@ -1043,6 +1043,13 @@ static unsigned long shrink_inactive_lis > struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); > int lumpy_reclaim = 0; > > + if (!scanning_global_lru(sc)) > + printk("shrink inactive %s count=%lu scan=%lu\n", > + file ? "file" : "anon", > + mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, > + LRU_INACTIVE_ANON + 2 * !!file), > + max_scan); > > and these commands: > > mkdir /cgroup/0 > echo 100M > /cgroup/0/memory.limit_in_bytes > echo $$ > /cgroup/0/tasks > cp /tmp/10G /dev/null And I can reduce the limit to 1M and 500K without triggering OOM: [ 963.329746] shrink inactive file count=201 scan=32 [ 963.335076] shrink inactive file count=177 scan=15 [ 963.350719] shrink inactive file count=201 scan=32 [ 963.356020] shrink inactive file count=177 scan=15 [ 963.371914] shrink inactive file count=201 scan=32 [ 963.377225] shrink inactive file count=177 scan=15 [ 963.393022] shrink inactive file count=201 scan=32 [ 963.398362] shrink inactive file count=177 scan=15 [ 1103.951251] shrink inactive file count=70 scan=32 [ 1104.054242] shrink inactive file count=46 scan=32 [ 1104.077381] shrink inactive file count=70 scan=32 [ 1104.083095] shrink inactive file count=73 scan=32 [ 1104.088513] shrink inactive file count=45 scan=2 [ 1104.113545] shrink inactive file count=70 scan=32 [ 1104.118915] shrink inactive file count=73 scan=32 [ 1104.124612] shrink inactive file count=45 scan=2 [ 1104.130093] shrink inactive file count=69 scan=32 So the patch is pretty safe for tiny mem cgroups. Thanks, Fengguang > before patch: > > [ 3682.646008] shrink inactive file count=25535 scan=6 > [ 3682.661548] shrink inactive file count=25535 scan=6 > [ 3682.666933] shrink inactive file count=25535 scan=6 > [ 3682.682865] shrink inactive file count=25535 scan=6 > [ 3682.688572] shrink inactive file count=25535 scan=6 > [ 3682.703908] shrink inactive file count=25535 scan=6 > [ 3682.709431] shrink inactive file count=25535 scan=6 > > after patch: > > [ 223.146544] shrink inactive file count=25531 scan=32 > [ 223.152060] shrink inactive file count=25507 scan=10 > [ 223.167503] shrink inactive file count=25531 scan=32 > [ 223.173426] shrink inactive file count=25507 scan=10 > [ 223.188764] shrink inactive file count=25531 scan=32 > [ 223.194270] shrink inactive file count=25507 scan=10 > [ 223.209885] shrink inactive file count=25531 scan=32 > [ 223.215388] shrink inactive file count=25507 scan=10 > > Before patch, the inactive list is over scanned by 30/6=5 times; > After patch, it is over scanned by 64/42=1.5 times. It's much better, > and can be further improved if necessary. > > > Acked-by: Balbir Singh > > Thanks! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org