Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755011Ab1FJIMY (ORCPT ); Fri, 10 Jun 2011 04:12:24 -0400 Received: from cantor.suse.de ([195.135.220.2]:43318 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754497Ab1FJIMV (ORCPT ); Fri, 10 Jun 2011 04:12:21 -0400 Date: Fri, 10 Jun 2011 10:12:19 +0200 From: Michal Hocko To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "nishimura@mxp.nes.nec.co.jp" , "bsingharora@gmail.com" , Ying Han Subject: Re: [BUGFIX][PATCH v3] memcg: fix behavior of per cpu charge cache draining. Message-ID: <20110610081218.GC4832@tiehlicka.suse.cz> References: <20110609093045.1f969d30.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110609093045.1f969d30.kamezawa.hiroyu@jp.fujitsu.com> 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: 3534 Lines: 94 On Thu 09-06-11 09:30:45, KAMEZAWA Hiroyuki wrote: > From 0ebd8a90a91d50c512e7c63e5529a22e44e84c42 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki > Date: Wed, 8 Jun 2011 13:51:11 +0900 > Subject: [PATCH] Fix behavior of per-cpu charge cache draining in memcg. > > For performance, memory cgroup caches some "charge" from res_counter > into per cpu cache. This works well but because it's cache, > it needs to be flushed in some cases. Typical cases are > 1. when someone hit limit. > 2. when rmdir() is called and need to charges to be 0. > > But "1" has problem. > > Recently, with large SMP machines, we many kworker runs because > of flushing memcg's cache. Bad things in implementation are > > a) it's called before calling try_to_free_mem_cgroup_pages() > so, it's called immidiately when a task hit limit. > (I though it was better to avoid to run into memory reclaim. > But it was wrong decision.) > > b) Even if a cpu contains a cache for memcg not related to > a memcg which hits limit, drain code is called. > > This patch fixes a) and b) by > > A) delay calling of flushing until one run of try_to_free... > Then, the number of calling is decreased. > B) check percpu cache contains a useful data or not. > plus > C) check asynchronous percpu draining doesn't run. > > BTW, why this patch relpaces atomic_t counter with mutex is > to guarantee a memcg which is pointed by stock->cacne is > not destroyed while we check css_id. > > Reported-by: Ying Han > Reviewed-by: Michal Hocko > Signed-off-by: KAMEZAWA Hiroyuki > > Changelog: > - fixed typo. > - fixed rcu_read_lock() and add strict mutal execution between > asynchronous and synchronous flushing. It's requred for validness > of cached pointer. > - add root_mem->use_hierarchy check. > --- > mm/memcontrol.c | 54 +++++++++++++++++++++++++++++++++++------------------- > 1 files changed, 35 insertions(+), 19 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index bd9052a..3baddcb 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c [...] > static struct mem_cgroup_per_zone * > mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid) > @@ -1670,8 +1670,6 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > victim = mem_cgroup_select_victim(root_mem); > if (victim == root_mem) { > loop++; > - if (loop >= 1) > - drain_all_stock_async(); > if (loop >= 2) { > /* > * If we have not been able to reclaim > @@ -1723,6 +1721,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > return total; > } else if (mem_cgroup_margin(root_mem)) > return total; > + drain_all_stock_async(root_mem); > } > return total; > } I still think that we pointlessly reclaim even though we could have a lot of pages pre-charged in the cache (the more CPUs we have the more significant this might be). Now that drain_all_stock_async is more targeted with your patch doesn't it make sense to call it before we start what-ever reclaim and call mem_cgroup_margin right after? -- 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/