linux-kernel - Re: [PATCH 3/9] bio-cgroup controller

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Message-Id: <20090417112433.085ed604.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 17 Apr 2009 11:24:33 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
Cc:	Andrea Righi <righi.andrea@...il.com>,
	Paul Menage <menage@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>, agk@...rceware.org,
	akpm@...ux-foundation.org, axboe@...nel.dk, baramsori72@...il.com,
	Carl Henrik Lunde <chlunde@...g.uio.no>,
	dave@...ux.vnet.ibm.com, Divyesh Shah <dpshah@...gle.com>,
	eric.rannaud@...il.com, fernando@....ntt.co.jp,
	Hirokazu Takahashi <taka@...inux.co.jp>,
	Li Zefan <lizf@...fujitsu.com>, matt@...ehost.com,
	dradford@...ehost.com, ngupta@...gle.com, randy.dunlap@...cle.com,
	roberto@...it.it, Ryo Tsuruta <ryov@...inux.co.jp>,
	Satoshi UCHIDA <s-uchida@...jp.nec.com>,
	subrata@...ux.vnet.ibm.com, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/9] bio-cgroup controller

On Fri, 17 Apr 2009 10:49:43 +0900
Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp> wrote:

> Hi,
> 
> I have a few question.
>    - I have not yet fully understood how your controller are using
>      bio_cgroup. If my view is wrong please tell me.
> 
> o In my view, bio_cgroup's implementation strongly depends on
>    page_cgoup's. Could you explain for what purpose does this
>    functionality itself should be implemented as cgroup subsystem?
>    Using page_cgoup and implementing tracking APIs is not enough?

I'll definitely do "Nack" to add full bio-cgroup members to page_cgroup.
Now, page_cgroup is 40bytes(in 64bit arch.) And all of them are allocated at
boot time as memmap. (and add member to struct page is much harder ;)

IIUC, feature for "tracking bio" is just necesary for pages for I/O.
So, I think it's much better to add misc. information to struct bio not to the page.
But, if people want to add "small hint" to struct page or struct page_cgroup
for tracking buffered I/O, I'll give you help as much as I can.
Maybe using "unused bits" in page_cgroup->flags is a choice with no overhead.

Thanks,
-Kame

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