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Message-ID: <20090821014628.GA31483@localhost>
Date: Fri, 21 Aug 2009 09:46:28 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Andrew Morton <akpm@...ux-foundation.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Avi Kivity <avi@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>,
"Dike, Jeffrey G" <jeffrey.g.dike@...el.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Christoph Lameter <cl@...ux-foundation.org>,
Mel Gorman <mel@....ul.ie>,
LKML <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
"menage@...gle.com" <menage@...gle.com>
Subject: Re: [PATCH -v2] mm: do batched scans for mem_cgroup
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 <fengguang.wu@...el.com> [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 <fengguang.wu@...el.com> 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 <riel@...hat.com>
> > > > > CC: Minchan Kim <minchan.kim@...il.com>
> > > > > CC: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > > > > CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > > > > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > > > > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > > > > ---
> > > >
> > > > 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 <balbir@...ux.vnet.ibm.com>
>
> Thanks!
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