[RFC PATCH 0/5] powerpc/mm/slice: improve slice speed and stack use

[Nicholas Piggin <npiggin@gmail.com>]

This series intends to improve performance and reduce stack
consumption in the slice allocation code. It does it by keeping slice
masks in the mm_context rather than compute them for each allocation,
and by reducing bitmaps and slice_masks from stacks, using pointers
instead where possible.

checkstack.pl gives, before:
0x00000de4 slice_get_unmapped_area [slice.o]:           656
0x00001b4c is_hugepage_only_range [slice.o]:            512
0x0000075c slice_find_area_topdown [slice.o]:           416
0x000004c8 slice_find_area_bottomup.isra.1 [slice.o]:   272
0x00001aa0 slice_set_range_psize [slice.o]:             240
0x00000a64 slice_find_area [slice.o]:                   176
0x00000174 slice_check_fit [slice.o]:                   112

after:
0x00000d70 slice_get_unmapped_area [slice.o]:           320
0x000008f8 slice_find_area [slice.o]:                   144
0x00001860 slice_set_range_psize [slice.o]:             144
0x000018ec is_hugepage_only_range [slice.o]:            144
0x00000750 slice_find_area_bottomup.isra.4 [slice.o]:   128

The benchmark in https://github.com/linuxppc/linux/issues/49 gives, before:
$ time ./slicemask 
real	0m20.712s
user	0m5.830s
sys	0m15.105s

after:
$ time ./slicemask 
real	0m13.197s
user	0m5.409s
sys	0m7.779s

Thanks,
Nick

Nicholas Piggin (5):
  powerpc/mm/slice: pass pointers to struct slice_mask where possible
  powerpc/mm/slice: implement a slice mask cache
  powerpc/mm/slice: implement slice_check_range_fits
  powerpc/mm/slice: Use const pointers to cached slice masks where
    possible
  powerpc/mm/slice: use the dynamic high slice size to limit bitmap
    operations

 arch/powerpc/include/asm/book3s/64/mmu.h |  20 +-
 arch/powerpc/mm/slice.c                  | 302 +++++++++++++++++++------------
 2 files changed, 204 insertions(+), 118 deletions(-)

-- 
2.15.1