From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 3/5] writeback: dirty rate control
Date: Tue, 09 Aug 2011 19:02:02 +0200
Message-ID: <1312909322.1083.52.camel@twins>
References: <20110806084447.388624428@intel.com>
	 <20110806094526.878435971@intel.com>
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Cc: linux-fsdevel@vger.kernel.org, Andrew Morton
 <akpm@linux-foundation.org>,  Jan Kara <jack@suse.cz>, Christoph Hellwig
 <hch@lst.de>, Dave Chinner <david@fromorbit.com>, Greg Thelen
 <gthelen@google.com>, Minchan Kim <minchan.kim@gmail.com>, Vivek Goyal
 <vgoyal@redhat.com>,  Andrea Righi <arighi@develer.com>, linux-mm
 <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
To: Wu Fengguang <fengguang.wu@intel.com>
Return-path: <owner-linux-mm@kvack.org>
In-Reply-To: <20110806094526.878435971@intel.com>
Sender: owner-linux-mm@kvack.org
List-Id: linux-fsdevel.vger.kernel.org

On Sat, 2011-08-06 at 16:44 +0800, Wu Fengguang wrote:

> +       pos_bw =3D bw * pos_ratio >> BANDWIDTH_CALC_SHIFT;
> +       pos_bw++;  /* this avoids bdi->dirty_ratelimit get stuck in 0 */
> +

> +       pos_ratio *=3D bdi->avg_write_bandwidth;
> +       do_div(pos_ratio, dirty_bw | 1);
> +       ref_bw =3D bw * pos_ratio >> BANDWIDTH_CALC_SHIFT;=20

when written out that results in:

           bw * pos_ratio * bdi->avg_write_bandwidth
  ref_bw =3D -----------------------------------------
                         dirty_bw

which would suggest you write it like:

  ref_bw =3D div_u64((u64)pos_bw * bdi->avg_write_bandwidth, dirty_bw | 1);

since pos_bw is already bw * pos_ratio per the above.

Or am I missing something?

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