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    SubjectRe: [ 20/27] s390/mm: have 16 byte aligned struct pages
    On Thu, Dec 06, 2012 at 04:59:04PM -0800, Greg Kroah-Hartman wrote:
    > 3.6-stable review patch. If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Heiko Carstens <heiko.carstens@de.ibm.com>
    >
    > commit 4bffbb3455372a26816e364fb4448810f7014452 upstream.
    >
    > Select HAVE_ALIGNED_STRUCT_PAGE on s390, so that the slub allocator can make
    > use of compare and swap double for lockless updates. This increases the size
    > of struct page to 64 bytes (instead of 56 bytes), however the performance gain
    > justifies the increased size:
    >
    > - now excactly four struct pages fit into a single cache line; the
    > case that accessing a struct page causes two cache line loads
    > does not exist anymore.
    > - calculating the offset of a struct page within the memmap array
    > is only a simple shift instead of a more expensive multiplication.
    >
    > A "hackbench 200 process 200" run on a 32 cpu system did show an 8% runtime
    > improvement.
    >
    > Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
    > Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
    > Signed-off-by: CAI Qian <caiqian@redhat.com>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    Same as for 3.4: compare and swap double is not available for 3.6 on s390.



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