s390/mm: have 16 byte aligned struct pages

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>
This commit is contained in:
Heiko Carstens 2012-11-08 14:18:47 +01:00 committed by Martin Schwidefsky
parent 516bad44b9
commit 4bffbb3455

View File

@ -96,6 +96,7 @@ config S390
select HAVE_MEMBLOCK_NODE_MAP
select HAVE_CMPXCHG_LOCAL
select HAVE_CMPXCHG_DOUBLE
select HAVE_ALIGNED_STRUCT_PAGE if SLUB
select HAVE_VIRT_CPU_ACCOUNTING
select VIRT_CPU_ACCOUNTING
select ARCH_DISCARD_MEMBLOCK