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    SubjectRe: [patch 2/2] slab: always consider arch mandated alignment
    Christoph Lameter wrote:

    >On Wed, 26 Jul 2006, Manfred Spraul wrote:
    >>Signed-off-by: Manfred Spraul <>
    >Good bye to all those cacheline contentions that helped us find so many
    >race conditions in the past if we switched on SLAB_DEBUG. I thought this
    >was intentional?
    Relax, align is nearly never set.

    - kmalloc uses align==0, except if the architecture requests it
    - on my i386 system, the following users explicitely use align:
    * the pmd structure (4096: hardware requirement)
    * the pgd structure (32 bytes: hardware requirement)
    * the task structure (16 byte. fxsave)
    * sigqueue, pid: both request 4 byte alignment (based on __alignof__()).
    Doesn't affect debugging.

    From the other mail:

    >Thus the patch is correct, it's a bug in the slab allocator. If HWCACHE_ALIGN
    >> is set, then the allocator ignores align or ARCH_SLAB_MINALIGN.
    >But then Heiko does not want to set ARCH_SLAB_MINALIGN at all. This is not
    >the issue we are discussing. In the DEBUG case he wants
    >ARCH_KMALLOC_MINALIGN to be enforced even if ARCH_SLAB_MINALIGN is not
    The kmalloc caches are allocated with
    HWCACHE_ALIGN+ARCH_KMALLOC_MINALIGN. The logic in kmem_cache_create
    didn't handle that case correctly.
    On most architectures, ARCH_KMALLOC_MINALIGN is 0. Thus SLAB_DEBUG
    redzones everything.
    On s390, ARCH_KMALLOC_MINALIGN is 8. This disables redzoning.


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