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    SubjectRe: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous Memory Allocator added
    On 15 Jun 11 10:36, Marek Szyprowski wrote:
    > 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.

    We at Qualcomm have some platforms that have memory of different
    performance characteristics, some drivers will need a way of
    specifying that they need fast memory for an allocation (and would prefer
    an error if it is not available rather than a fallback to slower
    memory). It would also be bad if allocators who don't need fast
    memory got it "accidentally", depriving those who really need it.

    > >
    > > 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.

    We also have platforms where a well-defined part of the memory
    can be powered off, and other parts can't (or won't). We need a way
    to steer the place allocations come from to the memory that won't be
    turned off (so that CMA allocations are not an obstacle to memory
    hotremove).

    >
    > Best regards
    > --
    > Marek Szyprowski
    > Samsung Poland R&D Center
    >
    >
    >
    > _______________________________________________
    > Linaro-mm-sig mailing list
    > Linaro-mm-sig@lists.linaro.org
    > http://lists.linaro.org/mailman/listinfo/linaro-mm-sig

    Larry Bassel

    --
    Sent by an employee of the Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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