From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx140.postini.com [74.125.245.140]) by kanga.kvack.org (Postfix) with SMTP id 02DAA6B004F for ; Thu, 19 Jan 2012 21:21:09 -0500 (EST) Received: from m2.gw.fujitsu.co.jp (unknown [10.0.50.72]) by fgwmail6.fujitsu.co.jp (Postfix) with ESMTP id 2705B3EE0BD for ; Fri, 20 Jan 2012 11:21:08 +0900 (JST) Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 6255F2E68C4 for ; Fri, 20 Jan 2012 11:21:07 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 21DF5266D18 for ; Fri, 20 Jan 2012 11:21:07 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 02EDDE08001 for ; Fri, 20 Jan 2012 11:21:07 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.240.81.147]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id EFDD81DB803E for ; Fri, 20 Jan 2012 11:21:05 +0900 (JST) Date: Fri, 20 Jan 2012 11:19:47 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC] [PATCH 7/7 v2] memcg: make mem_cgroup_begin_update_stat to use global pcpu. Message-Id: <20120120111947.400b2b15.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20120119144712.GG13932@tiehlicka.suse.cz> References: <20120113173001.ee5260ca.kamezawa.hiroyu@jp.fujitsu.com> <20120113174510.5e0f6131.kamezawa.hiroyu@jp.fujitsu.com> <20120119144712.GG13932@tiehlicka.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: "linux-mm@kvack.org" , Ying Han , "hugh.dickins@tiscali.co.uk" , "hannes@cmpxchg.org" , cgroups@vger.kernel.org, "bsingharora@gmail.com" On Thu, 19 Jan 2012 15:47:12 +0100 Michal Hocko wrote: > On Fri 13-01-12 17:45:10, KAMEZAWA Hiroyuki wrote: > > From 3df71cef5757ee6547916c4952f04a263c1b8ddb Mon Sep 17 00:00:00 2001 > > From: KAMEZAWA Hiroyuki > > Date: Fri, 13 Jan 2012 17:07:35 +0900 > > Subject: [PATCH 7/7] memcg: make mem_cgroup_begin_update_stat to use global pcpu. > > > > Now, a per-cpu flag to show the memcg is under account moving is > > now implemented as per-memcg-per-cpu. > > > > So, when accessing this, we need to access memcg 1st. But this > > function is called even when status update doesn't occur. Then, > > accessing struct memcg is an overhead in such case. > > > > This patch removes per-cpu-per-memcg MEM_CGROUP_ON_MOVE and add > > per-cpu vairable to do the same work. For per-memcg, atomic > > counter is added. By this, mem_cgroup_begin_update_stat() will > > just access percpu variable in usual case and don't need to find & access > > memcg. This reduces overhead. > > I agree that move_account is not a hotpath and that we don't have > to optimize for it but I guess we can do better. If we use a cookie > parameter for > mem_cgroup_{begin,end}_update_stat(struct page *page, unsigned long *cookie) > then we can stab page_cgroup inside and use the last bit for > locked. Then we do not have to call lookup_page_cgroup again in > mem_cgroup_update_page_stat and just replace page by the cookie. > What do you think? > Because these routine is called as mem_cgroup_begin_update_stat() if (condition) set_page_flag mem_cgroup_update_stat() mem_cgroup_end_update_stat() In earlier version(not posted), I did so. Now, I don't because of 2 reasons. 1. I wonder it's better not to have extra arguments in begin_xxx it will be overhead itself. 2. my work's final purpose is integrate page_cgroup to struct page. If I can do, lookup_page_cgroup() cost will be almost 0 and we'll revert the cookie, finally. So, can't we keep this update routine simple for a while ? If we saw it's finally impossible to integrate page_cgroup to page, I'd like to consider 'cookie' again. BTW, If we use spinlock and need to do irq_disable() in begin_update_stat() we'll need to pass *flags... Thanks, -Kame -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org