linux-kernel - Re: [RFC] [PATCH 0/6] Provide cgroup isolation for buffered writes.

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Message-ID: <20110310181529.GF29464@redhat.com>
Date:	Thu, 10 Mar 2011 13:15:29 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Justin TerAvest <teravest@...gle.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	m-ikeda@...jp.nec.com, jaxboe@...ionio.com,
	linux-kernel@...r.kernel.org, ryov@...inux.co.jp,
	taka@...inux.co.jp, righi.andrea@...il.com,
	guijianfeng@...fujitsu.com, balbir@...ux.vnet.ibm.com,
	ctalbott@...gle.com, nauman@...gle.com, mrubin@...gle.com
Subject: Re: [RFC] [PATCH 0/6] Provide cgroup isolation for buffered writes.

On Thu, Mar 10, 2011 at 10:08:03AM -0800, Justin TerAvest wrote:

[..]
> > I don't like to increase size of page_cgroup but I think you can record
> > information without increasing size of page_cgroup.
> >
> > A) As Andrea did, encode it to pc->flags.
> >   But I'm afraid that there is a racy case because memory cgroup uses some
> >   test_and_set() bits.
> > B) I wonder why the information cannot be recorded in page->private.
> >   When page has buffers, you can record the information to buffer struct.
> >   About swapio (if you take care of), you can record information to bio.
> 
> Hi Kame,
> 
> I'm concerned that by using something like buffer_heads stored in
> page->private, we will only be supported on some filesystems and not
> others. In addition, I'm not sure if all filesystems attach buffer
> heads at the same time; if page->private is modified in the flusher
> thread, we might not be able to determine the thread that dirtied the
> page in the first place.

I think the person who dirtied the page can store the information in
page->private (assuming buffer heads were not generated) and if flusher
thread later ends up generating buffer heads and ends up modifying
page->private, this can be copied in buffer heads?

Thanks
Vivek
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