From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx136.postini.com [74.125.245.136]) by kanga.kvack.org (Postfix) with SMTP id EDB7B6B005D for ; Thu, 27 Sep 2012 14:34:06 -0400 (EDT) Message-ID: <50649B4C.8000208@parallels.com> Date: Thu, 27 Sep 2012 22:30:36 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v3 04/13] kmem accounting basic infrastructure References: <50634FC9.4090609@parallels.com> <20120926193417.GJ12544@google.com> <50635B9D.8020205@parallels.com> <20120926195648.GA20342@google.com> <50635F46.7000700@parallels.com> <20120926201629.GB20342@google.com> <50637298.2090904@parallels.com> <20120927120806.GA29104@dhcp22.suse.cz> <20120927143300.GA4251@mtj.dyndns.org> <20120927144307.GH3429@suse.de> <20120927145802.GC4251@mtj.dyndns.org> In-Reply-To: <20120927145802.GC4251@mtj.dyndns.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Mel Gorman , Michal Hocko , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, devel@openvz.org, linux-mm@kvack.org, Suleiman Souhlal , Frederic Weisbecker , David Rientjes , Johannes Weiner On 09/27/2012 06:58 PM, Tejun Heo wrote: > Hello, Mel. > > On Thu, Sep 27, 2012 at 03:43:07PM +0100, Mel Gorman wrote: >>> I'm not too convinced. First of all, the overhead added by kmemcg >>> isn't big. >> >> Really? >> >> If kmemcg was globally accounted then every __GFP_KMEMCG allocation in >> the page allocator potentially ends up down in >> __memcg_kmem_newpage_charge which >> >> 1. takes RCU read lock >> 2. looks up cgroup from task >> 3. takes a reference count >> 4. memcg_charge_kmem -> __mem_cgroup_try_charge >> 5. release reference count >> >> That's a *LOT* of work to incur for cgroups that do not care about kernel >> accounting. This is why I thought it was reasonable that the kmem accounting >> not be global. > > But that happens only when pages enter and leave slab and if it still > is significant, we can try to further optimize charging. Given that > this is only for cases where memcg is already in use and we provide a > switch to disable it globally, I really don't think this warrants > implementing fully hierarchy configuration. > Not totally true. We still have to match every allocation to the right cache, and that is actually our heaviest hit, responsible for the 2, 3 % we're seeing when this is enabled. It is the kind of path so hot that people frown upon branches being added, so I don't think we'll ever get this close to being free. -- 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