linux-kernel - Re: [PATCH/RFCv4 0/6] The Contiguous Memory Allocator framework

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Date:	Fri, 27 Aug 2010 10:37:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Michał Nazarewicz <m.nazarewicz@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Daniel Walker <dwalker@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Jonathan Corbet <corbet@....net>,
	Pawel Osciak <p.osciak@...sung.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Zach Pfeffer <zpfeffer@...eaurora.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Mel Gorman <mel@....ul.ie>, linux-media@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH/RFCv4 0/6] The Contiguous Memory Allocator framework

On Fri, 2010-08-27 at 17:16 +0900, KAMEZAWA Hiroyuki wrote:
> > How about changing following this?
> > The thing is MAX_ORDER is static. But we want to avoid too big
> > MAX_ORDER of whole zones to support devices which requires big
> > allocation chunk.
> > So let's add MAX_ORDER into each zone and then, each zone can have
> > different max order.
> > For example, while DMA[32], NORMAL, HIGHMEM can have normal size 11,
> > MOVABLE zone could have a 15.
> > 
> > This approach has a big side effect?

The side effect of increasing MAX_ORDER is that page allocations get
more expensive since the buddy tree gets larger, yielding more
splits/merges.

> Hm...need to check hard coded MAX_ORDER usages...I don't think
> side-effect is big. Hmm. But I think enlarging MAX_ORDER isn't an
> important thing. A code which strips contiguous chunks of pages from
> buddy allocator is a necessaty thing, as..

Right, once we can explicitly free the pages we want, crossing MAX_ORDER
isn't too hard like you say, we can simply continue with freeing the
next in order page.


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