Re: [PATCH V4 5/6] memcg: patch mem_cgroup_{begin,end}_update_page_stat() out if only root memcg exists

From: Glauber Costa <glommer@gmail.com>
To: Sha Zhengju <handai.szj@gmail.com>
Cc: Michal Hocko <mhocko@suse.cz>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Cgroups <cgroups@vger.kernel.org>,
	Greg Thelen <gthelen@google.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Wu Fengguang <fengguang.wu@intel.com>,
	Mel Gorman <mgorman@suse.de>, Sha Zhengju <handai.szj@taobao.com>
Subject: Re: [PATCH V4 5/6] memcg: patch mem_cgroup_{begin,end}_update_page_stat() out if only root memcg exists
Date: Mon, 15 Jul 2013 10:32:26 +0400	[thread overview]
Message-ID: <20130715063224.GA3745@localhost.localdomain> (raw)
In-Reply-To: <CAFj3OHXF+ZjnaDS2L6ZmuHPx20+7XC9r-s7Gh=_TYOr4Opr4Bw@mail.gmail.com>

On Fri, Jul 12, 2013 at 09:13:56PM +0800, Sha Zhengju wrote:
> Ooops.... it seems unreachable, change Glauber's email...
> 
> 
> On Fri, Jul 12, 2013 at 8:59 PM, Sha Zhengju <handai.szj@gmail.com> wrote:
> 
> > Add cc to Glauber
> >
Thanks

> >
> > On Thu, Jul 11, 2013 at 10:56 PM, Michal Hocko <mhocko@suse.cz> wrote:
> > > On Sat 06-07-13 01:33:43, Sha Zhengju wrote:
> > >> From: Sha Zhengju <handai.szj@taobao.com>
> > >>
> > >> If memcg is enabled and no non-root memcg exists, all allocated
> > >> pages belongs to root_mem_cgroup and wil go through root memcg
> > >> statistics routines.  So in order to reduce overheads after adding
> > >> memcg dirty/writeback accounting in hot paths, we use jump label to
> > >> patch mem_cgroup_{begin,end}_update_page_stat() in or out when not
> > >> used.
> > >
> > > I do not think this is enough. How much do you save? One atomic read.
> > > This doesn't seem like a killer.
> > >
> > > I hoped we could simply not account at all and move counters to the root
> > > cgroup once the label gets enabled.
> >
> > I have thought of this approach before, but it would probably run into
> > another issue, e.g, each zone has a percpu stock named ->pageset to
> > optimize the increment and decrement operations, and I haven't figure out a
> > simpler and cheaper approach to handle that stock numbers if moving global
> > counters to root cgroup, maybe we can just leave them and can afford the
> > approximation?
> >
> > Glauber have already done lots of works here, in his previous patchset he
> > also tried to move some global stats to root (
> > http://comments.gmane.org/gmane.linux.kernel.cgroups/6291). May I steal
> > some of your ideas here, Glauber? :P
> >
Of course. Please go ahead and keep me posted in my new address.

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