linux-kernel - Re: [PATCH 08/12] vmscan: Setup pagevec as late as possible in shrink_inactive

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Message-ID: <20100617103012.GA25567@csn.ul.ie>
Date:	Thu, 17 Jun 2010 11:30:13 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>
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>
Subject: Re: [PATCH 08/12] vmscan: Setup pagevec as late as possible in
	shrink_inactive_list()

On Wed, Jun 16, 2010 at 04:43:09PM -0700, Andrew Morton wrote:
> On Mon, 14 Jun 2010 12:17:49 +0100
> Mel Gorman <mel@....ul.ie> wrote:
> 
> > shrink_inactive_list() sets up a pagevec to release unfreeable pages. It
> > uses significant amounts of stack doing this. This patch splits
> > shrink_inactive_list() to take the stack usage out of the main path so
> > that callers to writepage() do not contain an unused pagevec on the
> > stack.
> 
> You can get the entire pagevec off the stack - just make it a
> static-to-shrink_inactive_list() pagevec-per-cpu.
> 

That idea has been floated as well. I didn't pursue it because Dave
said that giving page reclaim a stack diet was never going to be the
full solution so I didn't think the complexity was justified.

I kept some of the stack reduction stuff because a) it was there and b)
it would give kswapd extra headroom when calling writepage.

> Locking just requires pinning to a CPU.  We could trivially co-opt
> shrink_inactive_list()'s spin_lock_irq() for that, but
> pagevec_release() can be relatively expensive so it'd be sad to move
> that inside spin_lock_irq().  It'd be better to slap a
> get_cpu()/put_cpu() around the whole thing.
> 

It'd be something interesting to try out when nothing else was happening but
I'm not going to focus on it for the moment unless I think it will really
help this stack overflow problem.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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