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

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Date:	Thu, 04 Sep 2008 17:11:38 +0900
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,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

Hi Cristoph

> How does page allocator fastpath behavior fare with this pathch?

Don't worry it because

1. shrink_zone() isn't fastpath because any reclaim isn't fastpath.
2. buddy combining on __free_one_page() isn't fastpath because
   any buddy combining isn't fastpath. (*)

(*)
all modern allocator have delayed buddy combining mecanism
because buddy combining increase cache miss.
(please imazine address X+1 is freed when address X is cold.
 combining cause next alloc get address X, then caller see cold page)

at least, allocator's fastpath should avoid its combining IMHO.

Unfortunately the linux buddy's one is limited because
zone->pcp only cache order-0 page.

Then, higher order pages's free always use slow path now.
but it isn't his patch failure.

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