Date: Fri, 2 Jul 2010 12:33:15 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mel@csn.ul.ie>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
       linux-mm@kvack.org, Dave Chinner <david@fromorbit.com>,
       Chris Mason <chris.mason@oracle.com>, Nick Piggin <npiggin@suse.de>,
       Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
       Christoph Hellwig <hch@infradead.org>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 0/14] Avoid overflowing of stack during page reclaim V3
Message-Id: <20100702123315.667c6eac.akpm@linux-foundation.org>
In-Reply-To: <1277811288-5195-1-git-send-email-mel@csn.ul.ie>
References: <1277811288-5195-1-git-send-email-mel@csn.ul.ie>
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On Tue, 29 Jun 2010 12:34:34 +0100
Mel Gorman <mel@csn.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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