From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id C8CDA8D0040 for ; Mon, 28 Mar 2011 05:48:25 -0400 (EDT) Date: Mon, 28 Mar 2011 11:48:20 +0200 From: Michal Hocko Subject: Re: [PATCH] memcg: update documentation to describe usage_in_bytes Message-ID: <20110328094820.GC5693@tiehlicka.suse.cz> References: <20110321102420.GB26047@tiehlicka.suse.cz> <20110322091014.27677ab3.kamezawa.hiroyu@jp.fujitsu.com> <20110322104723.fd81dddc.nishimura@mxp.nes.nec.co.jp> <20110322073150.GA12940@tiehlicka.suse.cz> <20110323092708.021d555d.nishimura@mxp.nes.nec.co.jp> <20110323133517.de33d624.kamezawa.hiroyu@jp.fujitsu.com> <20110328085508.c236e929.nishimura@mxp.nes.nec.co.jp> <20110328132550.08be4389.nishimura@mxp.nes.nec.co.jp> <20110328074341.GA5693@tiehlicka.suse.cz> <20110328181127.b8a2a1c5.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110328181127.b8a2a1c5.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: Daisuke Nishimura , Andrew Morton , linux-mm@kvack.org, LKML On Mon 28-03-11 18:11:27, KAMEZAWA Hiroyuki wrote: > On Mon, 28 Mar 2011 09:43:42 +0200 > Michal Hocko wrote: > > > On Mon 28-03-11 13:25:50, Daisuke Nishimura wrote: > > > From: Daisuke Nishimura [...] > > > +5.5 usage_in_bytes > > > + > > > +As described in 2.1, memory cgroup uses res_counter for tracking and limiting > > > +the memory usage. memory.usage_in_bytes shows the current res_counter usage for > > > +memory, and DOESN'T show a actual usage of RSS and Cache. It is usually bigger > > > +than the actual usage for a performance improvement reason. > > > > Isn't an explicit mention about caching charges better? > > > > It's difficult to distinguish which is spec. and which is implemnation details... Sure. At least commit log should contain the implementation details IMO, though. > > My one here ;) > == > 5.5 usage_in_bytes > > For efficiency, as other kernel components, memory cgroup uses some optimization to > avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the > method and doesn't show 'exact' value of usage, it's an fuzz value for efficient > access. (Of course, when necessary, it's synchronized.) > In usual, the value (RSS+CACHE) in memory.stat shows more exact value. IOW, - In usual, the value (RSS+CACHE) in memory.stat shows more exact value. IOW, + (RSS+CACHE) value from memory.stat shows more exact value and should be used + by userspace. IOW, ? > usage_in_bytes is less exact than memory.stat. The error will be larger on the larger > hardwares which have many cpus and tasks. > == > > Hmm ? Looks much better. Thanks -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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