Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753649Ab1FJHgw (ORCPT ); Fri, 10 Jun 2011 03:36:52 -0400 Received: from cantor.suse.de ([195.135.220.2]:42012 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752211Ab1FJHgv (ORCPT ); Fri, 10 Jun 2011 03:36:51 -0400 Date: Fri, 10 Jun 2011 09:36:38 +0200 From: Michal Hocko To: Ying Han , Johannes Weiner Cc: 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 Subject: Re: [patch 4/8] memcg: rework soft limit reclaim Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110609150026.GD3994@tiehlicka.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4027 Lines: 99 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 selects > [...] > > >> 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, > > >> ? ? ? ? ? ? ? ?unsigned long reclaimed = sc->nr_reclaimed; > > >> ? ? ? ? ? ? ? ?unsigned long scanned = sc->nr_scanned; > > >> ? ? ? ? ? ? ? ?unsigned long nr_reclaimed; > > >> + ? ? ? ? ? ? ? int epriority = priority; > > >> + > > >> + ? ? ? ? ? ? ? if (mem_cgroup_soft_limit_exceeded(root, mem)) > > >> + ? ? ? ? ? ? ? ? ? ? ? epriority -= 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 design > > > 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: > > throttle_vm_writeout(sc->gfp_mask); > > } > > > > +#define MEMCG_SOFTLIMIT_RECLAIM_PRIORITY 2 > > + > > static void shrink_zone(int priority, struct zone *zone, > > struct scan_control *sc) > > { > > @@ -2001,13 +2003,13 @@ static void shrink_zone(int priority, struct zone *zone, > > unsigned long reclaimed = sc->nr_reclaimed; > > unsigned long scanned = sc->nr_scanned; > > unsigned long nr_reclaimed; > > - int epriority = priority; > > > > - if (mem_cgroup_soft_limit_exceeded(root, mem)) > > - epriority -= 1; > > + if (!mem_cgroup_soft_limit_exceeded(root, mem) && > > + priority > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) > > + 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() && !mem_cgroup_soft_limit_exceeded(root, mem) && priority > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) continue; Maybe the condition would have to be more complex for per-cgroup background reclaim, though. > You would do quite a > lot of loops > (DEFAULT_PRIORITY-MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) * zones * memcg_count > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/