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    SubjectRe: [patch 02/41] cpu alloc: The allocator
    Christoph Lameter a écrit :
    > 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.
    >
    >
    >
    Hum, maybe, but then we broke modules that might request up to PAGE_SIZE
    alignement for their percpu section,
    if I read your 3rd patch correctly.

    Taking into account the ((unsigned long)area & (PAGE_SIZE-1)) offset in
    cpu_alloc()
    should give up to PAGE_SIZE alignment for free.





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