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Re: [PATCH 8/8] mm: vmscan: Do not writeback filesystem pages from kswap

To: Mel Gorman <mgorman@xxxxxxx>
Subject: Re: [PATCH 8/8] mm: vmscan: Do not writeback filesystem pages from kswapd
From: Johannes Weiner <jweiner@xxxxxxxxxx>
Date: Wed, 3 Aug 2011 13:37:06 +0200
Cc: Linux-MM <linux-mm@xxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, XFS <xfs@xxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Minchan Kim <minchan.kim@xxxxxxxxx>
In-reply-to: <1311265730-5324-9-git-send-email-mgorman@xxxxxxx>
References: <1311265730-5324-1-git-send-email-mgorman@xxxxxxx> <1311265730-5324-9-git-send-email-mgorman@xxxxxxx>
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@xxxxxxx>

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@xxxxxxxxxx>

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