Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755891Ab2FXKdR (ORCPT ); Sun, 24 Jun 2012 06:33:17 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:42669 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755710Ab2FXKdQ (ORCPT ); Sun, 24 Jun 2012 06:33:16 -0400 Date: Sun, 24 Jun 2012 18:32:58 +0800 From: Wanpeng Li To: Johannes Weiner Cc: Michal Hocko , Balbir Singh , KAMEZAWA Hiroyuki , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Gavin Shan , Wanpeng Li , linux-mm@kvack.org Subject: Re: [PATCH] mm/memcg: add MAX_CHARGE_BATCH to limit unnecessary charge overhead Message-ID: <20120624103258.GB10915@kernel> Reply-To: Wanpeng Li References: <1340504169-5344-1-git-send-email-liwp.linux@gmail.com> <20120624094614.GT27816@cmpxchg.org> <20120624100812.GA7095@kernel> <20120624101948.GU27816@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120624101948.GU27816@cmpxchg.org> 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: 4021 Lines: 113 On Sun, Jun 24, 2012 at 12:19:48PM +0200, Johannes Weiner wrote: >On Sun, Jun 24, 2012 at 06:08:26PM +0800, Wanpeng Li wrote: >> On Sun, Jun 24, 2012 at 11:46:14AM +0200, Johannes Weiner wrote: >> >On Sun, Jun 24, 2012 at 10:16:09AM +0800, Wanpeng Li wrote: >> >> From: Wanpeng Li >> >> >> >> Since exceeded unused cached charges would add pressure to >> >> mem_cgroup_do_charge, more overhead would burn cpu cycles when >> >> mem_cgroup_do_charge cause page reclaim or even OOM be triggered >> >> just for such exceeded unused cached charges. Add MAX_CHARGE_BATCH >> >> to limit max cached charges. >> >> >> >> Signed-off-by: Wanpeng Li >> >> --- >> >> mm/memcontrol.c | 16 ++++++++++++++++ >> >> 1 file changed, 16 insertions(+) >> >> >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> >> index 0e092eb..1ff317a 100644 >> >> --- a/mm/memcontrol.c >> >> +++ b/mm/memcontrol.c >> >> @@ -1954,6 +1954,14 @@ void mem_cgroup_update_page_stat(struct page *page, >> >> * TODO: maybe necessary to use big numbers in big irons. >> >> */ >> >> #define CHARGE_BATCH 32U >> >> + >> >> +/* >> >> + * Max size of charge stock. Since exceeded unused cached charges would >> >> + * add pressure to mem_cgroup_do_charge which will cause page reclaim or >> >> + * even oom be triggered. >> >> + */ >> >> +#define MAX_CHARGE_BATCH 1024U >> >> + >> >> struct memcg_stock_pcp { >> >> struct mem_cgroup *cached; /* this never be root cgroup */ >> >> unsigned int nr_pages; >> >> @@ -2250,6 +2258,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, >> >> unsigned int batch = max(CHARGE_BATCH, nr_pages); >> >> int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES; >> >> struct mem_cgroup *memcg = NULL; >> >> + struct memcg_stock_pcp *stock; >> >> int ret; >> >> >> >> /* >> >> @@ -2320,6 +2329,13 @@ again: >> >> rcu_read_unlock(); >> >> } >> >> >> >> + stock = &get_cpu_var(memcg_stock); >> >> + if (memcg == stock->cached && stock->nr_pages) { >> >> + if (stock->nr_pages > MAX_CHARGE_BATCH) >> >> + batch = nr_pages; >> >> + } >> >> + put_cpu_var(memcg_stock); >> > >> >The only way excessive stock can build up is if the charging task gets >> >rescheduled, after trying to consume stock a few lines above, to a cpu >> >it was running on when it built up stock in the past. >> > >> > consume_stock() >> > memcg != stock->cached: >> > return false >> > do_charge() >> > >> > refill_stock() >> > memcg == stock->cached: >> > stock->nr_pages += nr_pages >> >> __mem_cgroup_try_charge() { >> unsigned int batch = max(CHARGE_BATCH, nr_pages); >> [...] >> mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check); >> [...] >> if(batch > nr_pages) >> refill_stock(memcg, batch - nr_pages); >> } >> >> Consider this scenario, If one task wants to charge nr_pages = 1, >> then batch = max(32,1) = 32, this time 31 excess charges >> will be charged in mem_cgroup_do_charge and then add to stock by >> refill_stock. Generally there are many tasks in one memory cgroup and >> maybe charges frequency. In this situation, limit will reach soon, >> and cause mem_cgroup_reclaim to call try_to_free_mem_cgroup_pages. > >But the stock is not a black hole that gets built up for giggles! The >next time the processes want to charge a page on this cpu, they will >consume it from the stock. Not add more pages to it. Look at where >consume_stock() is called. if(nr_pages == 1 && consume_stock(memcg)) goto done; Only when charge one page will call consume_stock. You can see the codes in mem_cgroup_charge_common() which also call __mem_cgroup_try_charge, when both transparent huge and hugetlbfs pages, nr_pages will larger than 1. -- 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/