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 ESMTP id D9E426B0012 for ; Wed, 15 Jun 2011 18:58:04 -0400 (EDT) Received: from hpaq14.eem.corp.google.com (hpaq14.eem.corp.google.com [172.25.149.14]) by smtp-out.google.com with ESMTP id p5FMw1qD013635 for ; Wed, 15 Jun 2011 15:58:02 -0700 Received: from qyk32 (qyk32.prod.google.com [10.241.83.160]) by hpaq14.eem.corp.google.com with ESMTP id p5FMumtY006612 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for ; Wed, 15 Jun 2011 15:58:00 -0700 Received: by qyk32 with SMTP id 32so2591677qyk.15 for ; Wed, 15 Jun 2011 15:58:00 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110610073638.GA15403@tiehlicka.suse.cz> References: <1306909519-7286-1-git-send-email-hannes@cmpxchg.org> <1306909519-7286-5-git-send-email-hannes@cmpxchg.org> <20110609150026.GD3994@tiehlicka.suse.cz> <20110610073638.GA15403@tiehlicka.suse.cz> Date: Wed, 15 Jun 2011 15:57:59 -0700 Message-ID: Subject: Re: [patch 4/8] memcg: rework soft limit reclaim From: Ying Han Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Johannes Weiner , KAMEZAWA Hiroyuki , Daisuke Nishimura , Balbir Singh , Andrew Morton , Rik van Riel , Minchan Kim , KOSAKI Motohiro , Mel Gorman , Greg Thelen , Michel Lespinasse , "linux-mm@kvack.org" , linux-kernel On Fri, Jun 10, 2011 at 12:36 AM, Michal Hocko wrote: > On Thu 09-06-11 17:00:26, Michal Hocko wrote: >> On Thu 02-06-11 22:25:29, Ying Han wrote: >> > On Thu, Jun 2, 2011 at 2:55 PM, Ying Han wrote: >> > > On Tue, May 31, 2011 at 11:25 PM, Johannes Weiner wrote: >> > >> Currently, soft limit reclaim is entered from kswapd, where it sele= cts >> [...] >> > >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> > >> index c7d4b44..0163840 100644 >> > >> --- a/mm/vmscan.c >> > >> +++ b/mm/vmscan.c >> > >> @@ -1988,9 +1988,13 @@ static void shrink_zone(int priority, struct= zone *zone, >> > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unsigned long reclaimed =3D sc->nr_r= eclaimed; >> > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unsigned long scanned =3D sc->nr_sca= nned; >> > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unsigned long nr_reclaimed; >> > >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 int epriority =3D priority; >> > >> + >> > >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (mem_cgroup_soft_limit_exceeded(ro= ot, mem)) >> > >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 epriority -=3D 1; >> > > >> > > Here we grant the ability to shrink from all the memcgs, but only >> > > higher the priority for those exceed the soft_limit. That is a desig= n >> > > change >> > > for the "soft_limit" which giving a hint to which memcgs to reclaim >> > > from first under global memory pressure. >> > >> > >> > Basically, we shouldn't reclaim from a memcg under its soft_limit >> > unless we have trouble reclaim pages from others. >> >> Agreed. >> >> > Something like the following makes better sense: >> > >> > diff --git a/mm/vmscan.c b/mm/vmscan.c >> > index bdc2fd3..b82ba8c 100644 >> > --- a/mm/vmscan.c >> > +++ b/mm/vmscan.c >> > @@ -1989,6 +1989,8 @@ restart: >> > =A0 =A0 =A0 =A0 throttle_vm_writeout(sc->gfp_mask); >> > =A0} >> > >> > +#define MEMCG_SOFTLIMIT_RECLAIM_PRIORITY =A0 =A0 =A0 2 >> > + >> > =A0static void shrink_zone(int priority, struct zone *zone, >> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 struct= scan_control *sc) >> > =A0{ >> > @@ -2001,13 +2003,13 @@ static void shrink_zone(int priority, struct z= one *zone, >> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 unsigned long reclaimed =3D sc->nr_rec= laimed; >> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 unsigned long scanned =3D sc->nr_scann= ed; >> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 unsigned long nr_reclaimed; >> > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 int epriority =3D priority; >> > >> > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (mem_cgroup_soft_limit_exceeded(root,= mem)) >> > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 epriority -=3D 1; >> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!mem_cgroup_soft_limit_exceeded(root= , mem) && >> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 priority= > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) >> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 continue; >> >> yes, this makes sense but I am not sure about the right(tm) value of the >> MEMCG_SOFTLIMIT_RECLAIM_PRIORITY. 2 sounds too low. > > There is also another problem. I have just realized that this code path > is shared with the cgroup direct reclaim. We shouldn't care about soft > limit in such a situation. It would be just a wasting of cycles. So we > have to: > > if (current_is_kswapd() && > =A0 =A0 =A0 =A0!mem_cgroup_soft_limit_exceeded(root, mem) && > =A0 =A0 =A0 =A0priority > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) > =A0 =A0 =A0 =A0continue; Agreed. > > Maybe the condition would have to be more complex for per-cgroup > background reclaim, though. That would be the same logic for per-memcg direct reclaim. In general, we don't consider soft_limit unless the global memory pressure. So the condition could be something like= : > if ( global_reclaim(sc) && > =A0 =A0 =A0 =A0!mem_cgroup_soft_limit_exceeded(root, mem) && > =A0 =A0 =A0 =A0priority > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) > =A0 =A0 =A0 =A0continue; make sense? Thanks --Ying > >> You would do quite a >> lot of loops >> (DEFAULT_PRIORITY-MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) * zones * memcg_coun= t >> without any progress (assuming that all of them are under soft limit >> which doesn't sound like a totally artificial configuration) until you >> allow reclaiming from groups that are under soft limit. Then, when you >> finally get to reclaiming, you scan rather aggressively. >> >> Maybe something like 3/4 of DEFAULT_PRIORITY? You would get 3 times >> over all (unbalanced) zones and all cgroups that are above the limit >> (scanning max{1/4096+1/2048+1/1024, 3*SWAP_CLUSTER_MAX} of the LRUs for >> each cgroup) which could be enough to collect the low hanging fruit. > > -- > Michal Hocko > SUSE Labs > SUSE LINUX s.r.o. > Lihovarska 1060/12 > 190 00 Praha 9 > Czech Republic > -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org