From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Righi <andrea@betterlinux.com>
Subject: Re: [ATTEND] [LSF/MM TOPIC] Buffered writes throttling
Date: Tue, 6 Mar 2012 00:19:30 +0100
Message-ID: <20120305231930.GC7545@thinkpad>
References: <4F507453.1020604@suse.com>
 <20120302153322.GB26315@redhat.com>
 <20120305192226.GA3670@localhost>
 <20120305211114.GF18546@redhat.com>
 <20120305223029.GB16807@localhost>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Vivek Goyal <vgoyal@redhat.com>,
	Suresh Jayaraman <sjayaraman@suse.com>,
	lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.cz>,
	Greg Thelen <gthelen@google.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mail.betterlinux.com ([199.58.199.50]:55312 "EHLO
	mail.betterlinux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1757621Ab2CEXTe (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Mon, 5 Mar 2012 18:19:34 -0500
Content-Disposition: inline
In-Reply-To: <20120305223029.GB16807@localhost>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Mon, Mar 05, 2012 at 02:30:29PM -0800, Fengguang Wu wrote:
> On Mon, Mar 05, 2012 at 04:11:15PM -0500, Vivek Goyal wrote:
...
> > But looks like we don't much choice. As buffered writes can be controlled
> > at two levels, we probably need two knobs. Also controlling writes while
> > entring cache limits will be global and not per device (unlinke currnet
> > per device limit in blkio controller). Having separate control for "dirty
> > rate limit" leaves the scope for implementing write control at device
> > level in the future (As some people prefer that). In possibly two 
> > solutions can co-exist in future.
> 
> Good point. balance_dirty_pages() has no idea about the devices at
> all. So the rate limit for buffered writes can hardly be unified with
> the per-device rate limit for direct writes.
> 

I think balance_dirty_pages() can have an idea about devices. We can get
a reference to the right block device / request queue from the
address_space:

  bdev = mapping->host->i_sb->s_bdev;
  q = bdev_get_queue(bdev);

(NULL pointer dereferences apart).

-Andrea