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

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Message-ID: <4DF8AFB5.10205@vmware.com>
Date:	Wed, 15 Jun 2011 15:12:21 +0200
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
CC:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	Daniel Walker <dwalker@...eaurora.org>, linux-mm@...ck.org,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>,
	linaro-mm-sig@...ts.linaro.org,
	Jesse Barker <jesse.barker@...aro.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Ankita Garg <ankita@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-media@...r.kernel.org
Subject: Re: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous Memory Allocator
 added

On 06/15/2011 01:53 PM, Daniel Vetter wrote:
> 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).
>    

Indeed, IIRC on the meeting I pointed out that there is no way to 
generically solve the fragmentation problem without movable buffers. 
(I'd do it as a simple CMA backend to TTM). This is exactly the same 
problem as trying to fit buffers in a limited VRAM area.

/Thomas


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