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

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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