From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [RFC] writeback and cgroup
Date: Thu, 12 Apr 2012 16:37:19 -0400
Message-ID: <20120412203719.GL2207@redhat.com>
References: <20120403183655.GA23106@dhcp-172-17-108-109.mtv.corp.google.com>
	<20120404145134.GC12676@redhat.com>
	<20120407080027.GA2584@quack.suse.cz>
	<20120410180653.GJ21801@redhat.com>
	<20120410210505.GE4936@quack.suse.cz>
	<20120410212041.GP21801@redhat.com>
	<20120410222425.GF4936@quack.suse.cz>
	<20120411154005.GD16692@redhat.com>
	<20120411192231.GF16008@quack.suse.cz>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Cc: Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>, ctalbott-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, rni-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org,
	andrea-oIIqvOZpAevzfdHfmsDf5w@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, sjayaraman-IBi9RG/b67k@public.gmane.org,
	lsf-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	jmoyer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Fengguang Wu <fengguang.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
To: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
Return-path: <containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <20120411192231.GF16008-+0h/O2h83AeN3ZZ/Hiejyg@public.gmane.org>
List-Unsubscribe: <https://lists.linuxfoundation.org/mailman/options/containers>,
	<mailto:containers-request-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org?subject=unsubscribe>
List-Archive: <http://lists.linuxfoundation.org/pipermail/containers/>
List-Post: <mailto:containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>
List-Help: <mailto:containers-request-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org?subject=help>
List-Subscribe: <https://lists.linuxfoundation.org/mailman/listinfo/containers>,
	<mailto:containers-request-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org?subject=subscribe>
Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
List-Id: linux-fsdevel.vger.kernel.org

On Wed, Apr 11, 2012 at 09:22:31PM +0200, Jan Kara wrote:

[..]
> > >   Well, btrfs plays tricks with bdi's but there is a special bdi called
> > > "btrfs" which backs the whole filesystem and that is what's put in
> > > sb->s_bdi or in each inode's i_mapping->backing_dev_info. So we have a
> > > global bdi to work with.
> > 
> > Ok, that's good to know. How would we configure this special bdi? I am
> > assuming there is no backing device visible in /sys/block/<device>/queue/?
> > Same is true for network file systems.
>   Where should be the backing device visible? Now it's me who is lost :)

I mean how are we supposed to put cgroup throttling rules using cgroup
interface for network filesystems and for btrfs global bdi. Using "dev_t"
associated with bdi? I see that all the bdi's are showing up in
/sys/class/bdi, but how do I know which one I am intereste in or which
one belongs to filesystem I am interestd in putting throttling rule on.

For block devices, we simply use "major:min limit" format to write to
a cgroup file and this configuration will sit in one of the per queue
per cgroup data structure.

I am assuming that when you say throttling should happen at bdi, you
are thinking of maintaining per cgroup per bdi data structures and user
is somehow supposed to pass "bdi_maj:bdi_min  limit" through cgroup files?
If yes, how does one map a filesystem's bdi we want to put rules on?

Also, at request queue level we have bios and we throttle bios. At bdi
level, I think there are no bios yet. So somehow we got to deal with
pages. Not sure how exactly will throttling happen.

Thanks
Vivek