linux-kernel - Re: [RFC] Shared page accounting for memory cgroup

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Message-ID: <20100107071554.GO3059@balbir.in.ibm.com>
Date:	Thu, 7 Jan 2010 12:45:54 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC] Shared page accounting for memory cgroup

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-01-06 16:12:11]:

> On Wed, 6 Jan 2010 12:31:50 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > > No. If it takes long time, locking fork()/exit() for such long time is the bigger
> > > issue.
> > > I recommend you to add memacct subsystem to sum up RSS of all processes's RSS counting
> > > under a cgroup.  Althoght it may add huge costs in page fault path but implementation
> > > will be very simple and will not hurt realtime ops.
> > > There will be no terrible race, I guess.
> > >
> > 
> > But others hold that lock as well, simple thing like listing tasks and
> > moving tasks, etc. I expect the usage of shared to be in the same
> > range.
> > 
> 
> And piles up costs ? I think cgroup guys should pay attention to fork/exit
> costs more. Now, it gets slower and slower.
> In that point, I never like migrate-at-task-move work in cpuset and memcg.
> 
> My 1st objection to this patch is this "shared" doesn't mean "shared between
> cgroup" but means "shared between processes".
> I think it's of no use and no help to users.
>

So what in your opinion would help end users? My concern is that as
we make progress with memcg, we account only for privately used pages
with no hint/data about the real usage (shared within or with other
cgroups). How do we decide if one cgroup is really heavy?
 
> And implementation is 2nd thing.
> 

More details on your concern, please!

-- 
	Balbir
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