From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Wu Fengguang <fengguang.wu@intel.com>
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>
Subject: Re: [PATCH 14/18] writeback: control dirty pause time
Date: Tue, 06 Sep 2011 17:51:25 +0200 [thread overview]
Message-ID: <1315324285.14232.16.camel@twins> (raw)
In-Reply-To: <20110904020916.460538138@intel.com>
On Sun, 2011-09-04 at 09:53 +0800, Wu Fengguang wrote:
> plain text document attachment (max-pause-adaption)
> The dirty pause time shall ultimately be controlled by adjusting
> nr_dirtied_pause, since there is relationship
>
> pause = pages_dirtied / task_ratelimit
>
> Assuming
>
> pages_dirtied ~= nr_dirtied_pause
> task_ratelimit ~= dirty_ratelimit
>
> We get
>
> nr_dirtied_pause ~= dirty_ratelimit * desired_pause
>
> Here dirty_ratelimit is preferred over task_ratelimit because it's
> more stable.
>
> It's also important to limit possible large transitional errors:
>
> - bw is changing quickly
> - pages_dirtied << nr_dirtied_pause on entering dirty exceeded area
> - pages_dirtied >> nr_dirtied_pause on btrfs (to be improved by a
> separate fix, but still expect non-trivial errors)
>
> So we end up using the above formula inside clamp_val().
>
> The best test case for this code is to run 100 "dd bs=4M" tasks on
> btrfs and check its pause time distribution.
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> mm/page-writeback.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> --- linux-next.orig/mm/page-writeback.c 2011-08-29 19:08:43.000000000 +0800
> +++ linux-next/mm/page-writeback.c 2011-08-29 19:08:44.000000000 +0800
> @@ -1193,7 +1193,20 @@ pause:
> if (!dirty_exceeded && bdi->dirty_exceeded)
> bdi->dirty_exceeded = 0;
>
> - current->nr_dirtied_pause = dirty_poll_interval(nr_dirty, dirty_thresh);
> + if (pause == 0)
> + current->nr_dirtied_pause =
> + dirty_poll_interval(nr_dirty, dirty_thresh);
> + else if (period <= max_pause / 4 &&
> + pages_dirtied >= current->nr_dirtied_pause)
> + current->nr_dirtied_pause = clamp_val(
> + dirty_ratelimit * (max_pause / 2) / HZ,
> + pages_dirtied + pages_dirtied / 8,
> + pages_dirtied * 4);
> + else if (pause >= max_pause)
> + current->nr_dirtied_pause = 1 | clamp_val(
> + dirty_ratelimit * (max_pause * 3/8)/HZ,
> + pages_dirtied / 4,
> + pages_dirtied * 7/8);
>
I very much prefer { } over multi line stmts, even if not strictly
needed.
I'm also not quite sure why pause==0 is a special case, also, do the two
other line segments connect on the transition point?
--
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next prev parent reply other threads:[~2011-09-06 15:51 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-04 1:53 [PATCH 00/18] IO-less dirty throttling v11 Wu Fengguang
2011-09-04 1:53 ` [PATCH 01/18] writeback: account per-bdi accumulated dirtied pages Wu Fengguang
2011-09-04 1:53 ` [PATCH 02/18] writeback: dirty position control Wu Fengguang
2011-09-05 15:02 ` Peter Zijlstra
2011-09-06 2:10 ` Wu Fengguang
2011-09-05 15:05 ` Peter Zijlstra
2011-09-06 2:43 ` Wu Fengguang
2011-09-06 18:20 ` Vivek Goyal
2011-09-08 2:53 ` Wu Fengguang
2011-11-12 5:44 ` Nai Xia
2011-09-04 1:53 ` [PATCH 03/18] writeback: dirty rate control Wu Fengguang
2011-09-29 11:57 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 04/18] writeback: stabilize bdi->dirty_ratelimit Wu Fengguang
2011-09-04 1:53 ` [PATCH 05/18] writeback: per task dirty rate limit Wu Fengguang
2011-09-06 15:47 ` Peter Zijlstra
2011-09-06 23:27 ` Jan Kara
2011-09-06 23:34 ` Jan Kara
2011-09-07 7:27 ` Peter Zijlstra
2011-09-07 1:04 ` Wu Fengguang
2011-09-07 7:31 ` Peter Zijlstra
2011-09-07 11:00 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 06/18] writeback: IO-less balance_dirty_pages() Wu Fengguang
2011-09-06 12:13 ` Peter Zijlstra
2011-09-07 2:46 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 07/18] writeback: dirty ratelimit - think time compensation Wu Fengguang
2011-09-04 1:53 ` [PATCH 08/18] writeback: trace dirty_ratelimit Wu Fengguang
2011-09-04 1:53 ` [PATCH 09/18] writeback: trace balance_dirty_pages Wu Fengguang
2011-09-04 1:53 ` [PATCH 10/18] writeback: dirty position control - bdi reserve area Wu Fengguang
2011-09-06 14:09 ` Peter Zijlstra
2011-09-07 12:31 ` Wu Fengguang
2011-09-12 10:19 ` Peter Zijlstra
2011-09-18 14:17 ` Wu Fengguang
2011-09-18 14:37 ` Wu Fengguang
2011-09-18 14:47 ` Wu Fengguang
2011-09-28 14:02 ` Wu Fengguang
2011-09-28 14:50 ` Peter Zijlstra
2011-09-29 3:32 ` Wu Fengguang
2011-09-29 8:49 ` Peter Zijlstra
2011-09-29 11:05 ` Wu Fengguang
2011-09-29 12:15 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 11/18] block: add bdi flag to indicate risk of io queue underrun Wu Fengguang
2011-09-06 14:22 ` Peter Zijlstra
2011-09-07 2:37 ` Wu Fengguang
2011-09-07 7:31 ` Peter Zijlstra
2011-09-04 1:53 ` [PATCH 12/18] writeback: balanced_rate cannot exceed write bandwidth Wu Fengguang
2011-09-04 1:53 ` [PATCH 13/18] writeback: limit max dirty pause time Wu Fengguang
2011-09-06 14:52 ` Peter Zijlstra
2011-09-07 2:35 ` Wu Fengguang
2011-09-12 10:22 ` Peter Zijlstra
2011-09-18 14:23 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 14/18] writeback: control " Wu Fengguang
2011-09-06 15:51 ` Peter Zijlstra [this message]
2011-09-07 2:02 ` Wu Fengguang
2011-09-12 10:28 ` Peter Zijlstra
2011-09-04 1:53 ` [PATCH 15/18] writeback: charge leaked page dirties to active tasks Wu Fengguang
2011-09-06 16:16 ` Peter Zijlstra
2011-09-07 9:06 ` Wu Fengguang
2011-09-07 0:17 ` Jan Kara
2011-09-07 9:37 ` Wu Fengguang
2011-09-04 1:53 ` [PATCH 16/18] writeback: fix dirtied pages accounting on sub-page writes Wu Fengguang
2011-09-04 1:53 ` [PATCH 17/18] writeback: fix dirtied pages accounting on redirty Wu Fengguang
2011-09-06 16:18 ` Peter Zijlstra
2011-09-07 0:22 ` Jan Kara
2011-09-07 1:18 ` Wu Fengguang
2011-09-07 6:56 ` Christoph Hellwig
2011-09-07 8:19 ` Peter Zijlstra
2011-09-07 16:42 ` Jan Kara
2011-09-07 16:46 ` Christoph Hellwig
2011-09-08 8:51 ` Steven Whitehouse
2011-09-04 1:53 ` [PATCH 18/18] btrfs: fix dirtied pages accounting on sub-page writes Wu Fengguang
2011-09-07 13:32 ` [PATCH 00/18] IO-less dirty throttling v11 Wu Fengguang
2011-09-07 19:14 ` Trond Myklebust
2011-09-28 14:58 ` Christoph Hellwig
2011-09-29 4:11 ` Wu Fengguang
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