From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx180.postini.com [74.125.245.180]) by kanga.kvack.org (Postfix) with SMTP id 3A7B86B0002 for ; Mon, 13 May 2013 08:25:08 -0400 (EDT) Date: Mon, 13 May 2013 14:25:04 +0200 From: Michal Hocko Subject: Re: [PATCH V2 2/3] memcg: alter mem_cgroup_{update,inc,dec}_page_stat() args to memcg pointer Message-ID: <20130513122504.GA5246@dhcp22.suse.cz> References: <1368421410-4795-1-git-send-email-handai.szj@taobao.com> <1368421524-4937-1-git-send-email-handai.szj@taobao.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1368421524-4937-1-git-send-email-handai.szj@taobao.com> Sender: owner-linux-mm@kvack.org List-ID: To: Sha Zhengju Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, akpm@linux-foundation.org, hughd@google.com, gthelen@google.com, Sha Zhengju On Mon 13-05-13 13:05:24, Sha Zhengju wrote: > From: Sha Zhengju > > Change the first argument of mem_cgroup_{update,inc,dec}_page_stat() from > 'struct page *' to 'struct mem_cgroup *', and so move PageCgroupUsed(pc) > checking out of mem_cgroup_update_page_stat(). This is a prepare patch for > the following memcg page stat lock simplifying. No, please do not do this because it just spreads memcg specific code out of memcontrol.c. Besides that the patch is not correct. [...] > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1109,12 +1109,24 @@ void page_add_file_rmap(struct page *page) > { > bool locked; > unsigned long flags; > + struct page_cgroup *pc; > + struct mem_cgroup *memcg = NULL; > > mem_cgroup_begin_update_page_stat(page, &locked, &flags); > + pc = lookup_page_cgroup(page); > + > + rcu_read_lock(); > + memcg = pc->mem_cgroup; a) unnecessary RCU take for memcg disabled and b) worse KABOOM in that case as page_cgroup is NULL. We really do not want to put mem_cgroup_disabled() tests all over the place. The idea behind mem_cgroup_begin_update_page_stat was to be almost a noop for !memcg (and the real noop for !CONFIG_MEMCG). so Nak to this approach -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org