Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754178Ab1FPAdi (ORCPT ); Wed, 15 Jun 2011 20:33:38 -0400 Received: from smtp-out.google.com ([74.125.121.67]:61463 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752104Ab1FPAdg convert rfc822-to-8bit (ORCPT ); Wed, 15 Jun 2011 20:33:36 -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=hMDVwFqLtA4Zz/e6we0xPcWjuz87g4KVMmrsfIrR22XTbKKxL5C97Emeyu0J7Ox1tl 3wcWCOCbVflGCFhPjL4w== MIME-Version: 1.0 In-Reply-To: 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 17:33:32 -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: 4921 Lines: 130 On Wed, Jun 15, 2011 at 3:57 PM, Ying Han wrote: > 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? Also +bool mem_cgroup_soft_limit_exceeded(struct mem_cgroup *mem) +{ + return res_counter_soft_limit_excess(&mem->res); +} --Ying > > 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/