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    SubjectRe: [Linaro-mm-sig] [PATCH 08/10] mm: cma: Contiguous Memory Allocator added
    On 06/15/2011 12:37 AM, Arnd Bergmann wrote:
    > On Wednesday 15 June 2011 09:11:39 Marek Szyprowski wrote:
    >> I see your concerns, but I really wonder how to determine the properties
    >> of the global/default cma pool. You definitely don't want to give all
    >> available memory o CMA, because it will have negative impact on kernel
    >> operation (kernel really needs to allocate unmovable pages from time to
    >> time).
    > Exactly. This is a hard problem, so I would prefer to see a solution for
    > coming up with reasonable defaults.

    Is this a situation where passing the information from device tree might
    help? I know this does not help short term, but I am trying to
    understand the sorts of problems device tree can help solve.


    >> The only solution I see now is to provide Kconfig entry to determine
    >> the size of the global CMA pool, but this still have some issues,
    >> especially for multi-board kernels (each board probably will have
    >> different amount of RAM and different memory-consuming devices
    >> available). It looks that each board startup code still might need to
    >> tweak the size of CMA pool. I can add a kernel command line option for
    >> it, but such solution also will not solve all the cases (afair there
    >> was a discussion about kernel command line parameters for memory
    >> configuration and the conclusion was that it should be avoided).
    > The command line option can be a last resort if the heuristics fail,
    > but it's not much better than a fixed Kconfig setting.
    > How about a Kconfig option that defines the percentage of memory
    > to set aside for contiguous allocations?
    > Arnd
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