From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753161Ab1GZLVF (ORCPT <rfc822;w@1wt.eu>);
	Tue, 26 Jul 2011 07:21:05 -0400
Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:33529 "EHLO
	ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1753077Ab1GZLVA (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 26 Jul 2011 07:21:00 -0400
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: AvcDAKagLk55LCkBgWdsb2JhbAA2AQEEAUAgJQUMCQMOCjoUASoDKhenWhUBARYmJYh8wXUOhVNfBKNk
Date: Tue, 26 Jul 2011 21:20:55 +1000
From: Dave Chinner <david@fromorbit.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        XFS <xfs@oss.sgi.com>, Christoph Hellwig <hch@infradead.org>,
        Johannes Weiner <jweiner@redhat.com>,
        Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>,
        Rik van Riel <riel@redhat.com>, Minchan Kim <minchan.kim@gmail.com>
Subject: Re: [RFC PATCH 0/8] Reduce filesystem writeback from page reclaim v2
Message-ID: <20110726112055.GC8048@dastard>
References: <1311265730-5324-1-git-send-email-mgorman@suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1311265730-5324-1-git-send-email-mgorman@suse.de>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Jul 21, 2011 at 05:28:42PM +0100, Mel Gorman wrote:
> Warning: Long post with lots of figures. If you normally drink coffee
> and you don't have a cup, get one or you may end up with a case of
> keyboard face.

[snip]

> Overall, having kswapd avoiding writes does improve performance
> which is not a surprise. Dave asked "do we even need IO at all from
> reclaim?". On NUMA machines, the answer is "yes" unless the VM can
> wake the flusher thread to clean a specific node.

Great answer, Mel. ;)

> When kswapd never
> writes, processes can stall for significant periods of time waiting on
> flushers to clean the correct pages. If all writing is to be deferred
> to flushers, it must ensure that many writes on one node would not
> starve requests for cleaning pages on another node.

Ok, so that's a direction we need to work towards, then.

> I'm currently of the opinion that we should consider merging patches
> 1-7 and discuss what is required before merging. It can be tackled
> later how the flushers can prioritise writing of pages belonging to
> a particular zone before disabling all writes from reclaim.

Sounds reasonable to me.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com