linux-kernel - Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

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Message-Id: <20081003123545.EF5B.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Fri,  3 Oct 2008 12:41:41 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Andy Whitcroft <apw@...dowen.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/4] capture pages freed during direct reclaim for	allocation by the reclaimer

Hi Cristoph,

> >> At the beginning of reclaim just flush all pcp pages and then do not allow pcp
> >> refills again until reclaim is finished?
> > 
> > Not entirely, some pages could get trapped there for sure.  But it is
> > parallel allocations we are trying to guard against.  Plus we already flush
> > the pcp during reclaim for higher orders.
> 
> So we just would need to forbid refilling the pcp.
> 
> Parallel allocations are less a problem if the freed order 0 pages get merged
> immediately into the order 1 freelist. Of course that will only work 50% of
> the time but it will have a similar effect to this patch.

Ah, Right.
Could we hear why you like pcp disabling than Andy's patch?

Honestly, I think pcp has some problem.
But I avoid to change pcp because I don't understand its design.

Maybe, we should discuss currect pcp behavior?



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