linux-ext4 - Re: [patch 2/4] mm: writeback: distribute write pages across allowable zones

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Message-ID: <4E78DD10.4000900@redhat.com>
Date:	Tue, 20 Sep 2011 14:36:00 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <jweiner@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Minchan Kim <minchan.kim@...il.com>,
	Chris Mason <chris.mason@...cle.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>, xfs@....sgi.com,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/4] mm: writeback: distribute write pages across allowable
 zones

On 09/20/2011 09:45 AM, Johannes Weiner wrote:
> This patch allows allocators to pass __GFP_WRITE when they know in
> advance that the allocated page will be written to and become dirty
> soon.  The page allocator will then attempt to distribute those
> allocations across zones, such that no single zone will end up full of
> dirty, and thus more or less, unreclaimable pages.
>
> The global dirty limits are put in proportion to the respective zone's
> amount of dirtyable memory and allocations diverted to other zones
> when the limit is reached.
>
> For now, the problem remains for NUMA configurations where the zones
> allowed for allocation are in sum not big enough to trigger the global
> dirty limits, but a future approach to solve this can reuse the
> per-zone dirty limit infrastructure laid out in this patch to have
> dirty throttling and the flusher threads consider individual zones.
>
> Signed-off-by: Johannes Weiner<jweiner@...hat.com>

Reviewed-by: Rik van Riel <riel@...hat.com>

The amount of work done in a __GFP_WRITE allocation looks
a little daunting, but doing that a million times probably
outweighs waiting on the disk even once, so...
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