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    SubjectRe: [patch 02/41] cpu alloc: The allocator
    Christoph Lameter wrote:
    > On Fri, 30 May 2008, Eric Dumazet wrote:
    >
    >>> +static DEFINE_PER_CPU(UNIT_TYPE, area[UNITS]);
    >>>
    >> area[] is not guaranteed to be aligned on anything but 4 bytes.
    >>
    >> If someone then needs to call cpu_alloc(8, GFP_KERNEL, 8), it might get an non
    >> aligned result.
    >>
    >> Either you should add an __attribute__((__aligned__(PAGE_SIZE))),
    >> or take into account the real address of area[] in cpu_alloc() to avoid waste
    >> of up to PAGE_SIZE bytes
    >> per cpu.
    >
    > I think cacheline aligning should be sufficient. People should not
    > allocate large page aligned objects here.

    I'm a bit confused. Why is DEFINE_PER_CPU_SHARED_ALIGNED() conditioned on
    ifdef MODULE?

    #ifdef MODULE
    #define SHARED_ALIGNED_SECTION ".data.percpu"
    #else
    #define SHARED_ALIGNED_SECTION ".data.percpu.shared_aligned"
    #endif

    #define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \
    __attribute__((__section__(SHARED_ALIGNED_SECTION))) \
    PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name \
    ____cacheline_aligned_in_smp

    Thanks,
    Mike


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