• Heiko Carstens's avatar
    s390/mm: have 16 byte aligned struct pages · 4bffbb34
    Heiko Carstens authored
    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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
    Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
    4bffbb34
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