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

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Message-id: <000901cc2b37$4c21f030$e465d090$%szyprowski@samsung.com>
Date:	Wed, 15 Jun 2011 10:36:18 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'Arnd Bergmann' <arnd@...db.de>,
	'Zach Pfeffer' <zach.pfeffer@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org,
	'Daniel Walker' <dwalker@...eaurora.org>,
	'Daniel Stone' <daniels@...labora.com>, 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,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: RE: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous Memory Allocator
 added

Hello,

On Tuesday, June 14, 2011 10:42 PM Arnd Bergmann wrote:

> On Tuesday 14 June 2011 20:58:25 Zach Pfeffer wrote:
> > I've seen this split bank allocation in Qualcomm and TI SoCs, with
> > Samsung, that makes 3 major SoC vendors (I would be surprised if
> > Nvidia didn't also need to do this) - so I think some configurable
> > method to control allocations is necessarily. The chips can't do
> > decode without it (and by can't do I mean 1080P and higher decode is
> > not functionally useful). Far from special, this would appear to be
> > the default.
> 
> Thanks for the insight, that's a much better argument than 'something
> may need it'. Are those all chips without an IOMMU or do we also
> need to solve the IOMMU case with split bank allocation?
> 
> I think I'd still prefer to see the support for multiple regions split
> out into one of the later patches, especially since that would defer
> the question of how to do the initialization for this case and make
> sure we first get a generic way.
> 
> You've convinced me that we need to solve the problem of allocating
> memory from a specific bank eventually, but separating it from the
> one at hand (contiguous allocation) should help getting the important
> groundwork in at first.
>
> The possible conflict that I still see with per-bank CMA regions are:
> 
> * It completely destroys memory power management in cases where that
>   is based on powering down entire memory banks.

I don't think that per-bank CMA regions destroys memory power management
more than the global CMA pool. Please note that the contiguous buffers
(or in general dma-buffers) right now are unmovable so they don't fit
well into memory power management.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center


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