linux-kernel - Re: [PATCH 6/6] vmscan: Do not writeback pages in direct reclaim

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Message-ID: <20100611162523.GA24707@infradead.org>
Date:	Fri, 11 Jun 2010 12:25:23 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 6/6] vmscan: Do not writeback pages in direct reclaim

On Thu, Jun 10, 2010 at 11:17:06PM -0700, Andrew Morton wrote:
> As it stands, it would be wildly incautious to make a change like
> this without first working out why we're pulling so many dirty pages
> off the LRU tail, and fixing that.

Note that unlike the writepage vs writepages from kswapd which can
be fixed by the right tuning this is a black or white issue.  Writeback
from direct reclaim will kill your stack if the caller happens to be
the wrong one, and just making it happen less often is not a fix - it
must not happen at all.

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