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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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