Date: Wed, 28 Jul 2010 12:18:20 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "nishimura@mxp.nes.nec.co.jp" <nishimura@mxp.nes.nec.co.jp>,
        "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>,
        gthelen@google.com, m-ikeda@ds.jp.nec.com,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH 4/7][memcg] memcg use ID in page_cgroup
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On Tue, 27 Jul 2010 23:13:58 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:
 
> > > So the idea is that when a page is allocated, also store the blk_group
> > > id and once that page is submitted for writeback, we should be able
> > > to associate it to right blkio group?
> > > 
> > blk_cgroup id can be attached whenever you wants. please overwrite 
> > page_cgroup->blk_cgroup when it's necessary.
> 
> > Did you read Ikeda's patch ? I myself doesn't have patches at this point. 
> > This is just for make a room for recording blkio-ID, which was requested
> > for a year.
> 
> I have not read his patches yet. IIRC, previously there were issues
> regarding which group should be charged for the page. The person who
> allocated it or the thread which did last write to it etc... I guess
> we can sort that out later.
> 
> > 
> > Hmm, but page-allocation-time doesn't sound very good for me.
> > 
> 
> Why?
> 

As you wrote, by attaching ID when a page cache is added, we'll have
much chances of free-rider until it's paged out. So, adding some
reseting-owner point may be good. 

But considering real world usage, I may be wrong.
There will not be much free rider in real world, especially at write().
Then, page-allocation time may be good.

(Because database doesn't use page-cache, there will be no big random write
 application.)

Thanks,
-Kame

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