Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755821Ab1FOW6F (ORCPT ); Wed, 15 Jun 2011 18:58:05 -0400 Received: from smtp-out.google.com ([216.239.44.51]:59534 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752035Ab1FOW6C convert rfc822-to-8bit (ORCPT ); Wed, 15 Jun 2011 18:58:02 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=cJWMpGO3ERcOlP6wMQaRlKB1RaLHi0m231ZXSjetHkrEkB0LFanJWQx72CFwzsy3cg fog5dYsOBOKfukeYRi5Q== 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 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4588 Lines: 119 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 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; 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) && > ? ? ? ?!mem_cgroup_soft_limit_exceeded(root, mem) && > ? ? ? ?priority > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) > ? ? ? ?continue; make sense? Thanks --Ying > >> 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/