linux-kernel - Re: [PATCH 0/14] Avoid overflowing of stack during page reclaim V3

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Message-Id: <20100702123315.667c6eac.akpm@linux-foundation.org>
Date:	Fri, 2 Jul 2010 12:33:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	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>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 0/14] Avoid overflowing of stack during page reclaim V3

On Tue, 29 Jun 2010 12:34:34 +0100
Mel Gorman <mel@....ul.ie> wrote:

> Here is V3 that depends again on flusher threads to do writeback in
> direct reclaim rather than stack switching which is not something I'm
> likely to get done before xfs/btrfs are ignoring writeback in mainline
> (phd sucking up time).

IMO, implemetning stack switching for this is not a good idea.  We
_already_ have a way of doing stack-switching.  It's called
"schedule()".

The only reason I can see for implementing an in-place stack switch
would be if schedule() is too expensive.  And if we were to see
excessive context-switch overheads in this code path (and we won't)
then we should get in there and try to reduce the contect switch rate
first.

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