linux-kernel - Re: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous Memory Allocator added

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Message-Id: <201106221539.24044.arnd@arndb.de>
Date:	Wed, 22 Jun 2011 15:39:23 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	"'Hans Verkuil'" <hverkuil@...all.nl>,
	"'Daniel Walker'" <dwalker@...eaurora.org>,
	"'Jesse Barker'" <jesse.barker@...aro.org>,
	"'Mel Gorman'" <mel@....ul.ie>,
	"'KAMEZAWA Hiroyuki'" <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	"'Michal Nazarewicz'" <mina86@...a86.com>,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	"'Kyungmin Park'" <kyungmin.park@...sung.com>,
	"'Ankita Garg'" <ankita@...ibm.com>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous 
 Memory	Allocator added

On Wednesday 22 June 2011, Marek Szyprowski wrote:
> Sounds really good, but it might be really hard to implemnt, at least for
> CMA, because it needs to tweak parameters of memory management internal 
> structures very early, when buddy allocator has not been activated yet.

Why that? I would expect you can do the same that hugepages (used to) do
and just attempt high-order allocations. If they succeed, you can add them
as a CMA region and free them again, into the movable set of pages, otherwise
you just fail the  request from user space when the memory is already
fragmented.
 
> > These essentially fight over the same memory (though things are slightly
> > different with dynamic hugepages), and they all face the same basic problem
> > of getting as much for themselves without starving the other three.
> 
> I'm not sure we can solve all such issues in the first version. Maybe we should
> first have each of the above fully working in mainline separately and then
> start the integration works.

Yes, makes sense. We just need to be careful not to introduce user-visible
interfaces that we cannot change any more in the process.

	Arnd
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