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

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Message-ID: <BANLkTi=XTJuF4np7+rYHzJqWK20OxMrBsw@mail.gmail.com>
Date:	Wed, 15 Jun 2011 13:53:22 +0200
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	Ankita Garg <ankita@...ibm.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Jesse Barker <jesse.barker@...aro.org>,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 Tue, Jun 14, 2011 at 20:30, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 14 June 2011 18:58:35 Michal Nazarewicz wrote:
>> Ah yes, I forgot that separate regions for different purposes could
>> decrease fragmentation.
>
> That is indeed a good point, but having a good allocator algorithm
> could also solve this. I don't know too much about these allocation
> algorithms, but there are probably multiple working approaches to this.

imo no allocator algorithm is gonna help if you have comparably large,
variable-sized contiguous allocations out of a restricted address range.
It might work well enough if there are only a few sizes and/or there's
decent headroom. But for really generic workloads this would require
sync objects and eviction callbacks (i.e. what Thomas Hellstrom pushed
with ttm).

So if this is only a requirement on very few platforms and can be
cheaply fixed with multiple cma allocation areas (heck, we have
slabs for the same reasons in the kernel), it might be a sensible
compromise.
-Daniel
-- 
Daniel Vetter
daniel.vetter@...ll.ch - +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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