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