From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id 953A46B0074 for ; Tue, 14 May 2013 05:00:10 -0400 (EDT) Received: by mail-bk0-f44.google.com with SMTP id jk13so146947bkc.3 for ; Tue, 14 May 2013 02:00:09 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <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> <20130513122504.GA5246@dhcp22.suse.cz> Date: Tue, 14 May 2013 17:00:08 +0800 Message-ID: Subject: Re: [PATCH V2 2/3] memcg: alter mem_cgroup_{update,inc,dec}_page_stat() args to memcg pointer From: Sha Zhengju Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Cgroups , "linux-mm@kvack.org" , KAMEZAWA Hiroyuki , Andrew Morton , Hugh Dickins , Greg Thelen , Sha Zhengju On Mon, May 13, 2013 at 8:25 PM, Michal Hocko wrote: > 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). It's indeed an unwise behavior. How about also wrapping it in mm/memcontrol.c or memcontrol.h? > > so Nak to this approach -- Thanks, Sha -- 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