linux-kernel - Re: [PATCH 8/8] mm: vmscan: Do not writeback filesystem pages from kswapd

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Message-ID: <20110803113706.GF27199@redhat.com>
Date:	Wed, 3 Aug 2011 13:37:06 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 8/8] mm: vmscan: Do not writeback filesystem pages from
 kswapd

On Thu, Jul 21, 2011 at 05:28:50PM +0100, Mel Gorman wrote:
> Assuming that flusher threads will always write back dirty pages promptly
> then it is always faster for reclaimers to wait for flushers. This patch
> prevents kswapd writing back any filesystem pages.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Relying on the flushers may mean that every dirty page in the system
has to be written back before the pages from the zone of interest are
clean.

De-facto we have only one mechanism to stay on top of the dirty pages
from a per-zone perspective, and that is single-page writeout from
reclaim.

While we all agree that this sucks, we can not remove it unless we
have a replacement that makes zones reclaimable in a reasonable time
frame (or keep them reclaimable in the first place, what per-zone
dirty limits attempt to do).

As such, please include

Nacked-by: Johannes Weiner <jweiner@...hat.com>
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