linux-kernel - Re: [patch 2/2] mm: page-writeback: do not count anon pages as dirtyable memory

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Date:	Fri, 24 Jan 2014 18:25:52 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Tejun Heo <tj@...nel.org>, Mel Gorman <mgorman@...e.de>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] mm: page-writeback: do not count anon pages as dirtyable
 memory

On 01/24/2014 05:03 PM, Johannes Weiner wrote:
> The VM is currently heavily tuned to avoid swapping.  Whether that is
> good or bad is a separate discussion, but as long as the VM won't swap
> to make room for dirty cache, we can not consider anonymous pages when
> calculating the amount of dirtyable memory, the baseline to which
> dirty_background_ratio and dirty_ratio are applied.
> 
> A simple workload that occupies a significant size (40+%, depending on
> memory layout, storage speeds etc.) of memory with anon/tmpfs pages
> and uses the remainder for a streaming writer demonstrates this
> problem.  In that case, the actual cache pages are a small fraction of
> what is considered dirtyable overall, which results in an relatively
> large portion of the cache pages to be dirtied.  As kswapd starts
> rotating these, random tasks enter direct reclaim and stall on IO.
> 
> Only consider free pages and file pages dirtyable.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

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


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