[PATCH 08/10] powerpc/mm/slice: Use const pointers to cached slice masks where possible
Christophe LEROY
christophe.leroy at c-s.fr
Wed Mar 7 01:55:04 AEDT 2018
Le 06/03/2018 à 14:25, Nicholas Piggin a écrit :
> The slice_mask cache was a basic conversion which copied the slice
> mask into caller's structures, because that's how the original code
> worked. In most cases the pointer can be used directly instead, saving
> a copy and an on-stack structure.
>
> On POWER8, this increases vfork+exec+exit performance by 0.3%
> and reduces time to mmap+munmap a 64kB page by 2%.
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> arch/powerpc/mm/slice.c | 77 +++++++++++++++++++++----------------------------
> 1 file changed, 33 insertions(+), 44 deletions(-)
>
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 46daa1d1794f..086c31b8b982 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -472,10 +472,10 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> unsigned long flags, unsigned int psize,
> int topdown)
> {
> - struct slice_mask mask;
> struct slice_mask good_mask;
> struct slice_mask potential_mask;
> - struct slice_mask compat_mask;
> + const struct slice_mask *maskp;
> + const struct slice_mask *compat_maskp = NULL;
> int fixed = (flags & MAP_FIXED);
> int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
> unsigned long page_size = 1UL << pshift;
> @@ -509,22 +509,6 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> on_each_cpu(slice_flush_segments, mm, 1);
> }
>
> - /*
> - * init different masks
> - */
> - mask.low_slices = 0;
> -
> - /* silence stupid warning */;
> - potential_mask.low_slices = 0;
> -
> - compat_mask.low_slices = 0;
> -
> - if (SLICE_NUM_HIGH) {
> - bitmap_zero(mask.high_slices, SLICE_NUM_HIGH);
> - bitmap_zero(potential_mask.high_slices, SLICE_NUM_HIGH);
> - bitmap_zero(compat_mask.high_slices, SLICE_NUM_HIGH);
> - }
> -
> /* Sanity checks */
> BUG_ON(mm->task_size == 0);
> BUG_ON(mm->context.slb_addr_limit == 0);
> @@ -547,8 +531,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> /* First make up a "good" mask of slices that have the right size
> * already
> */
> - good_mask = *slice_mask_for_size(mm, psize);
> - slice_print_mask(" good_mask", &good_mask);
> + maskp = slice_mask_for_size(mm, psize);
>
> /*
> * Here "good" means slices that are already the right page size,
> @@ -572,11 +555,19 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> #ifdef CONFIG_PPC_64K_PAGES
> /* If we support combo pages, we can allow 64k pages in 4k slices */
> if (psize == MMU_PAGE_64K) {
> - compat_mask = *slice_mask_for_size(mm, MMU_PAGE_4K);
> + compat_maskp = slice_mask_for_size(mm, MMU_PAGE_4K);
> if (fixed)
> - slice_or_mask(&good_mask, &good_mask, &compat_mask);
> - }
> + slice_or_mask(&good_mask, maskp, compat_maskp);
> + else
> + slice_copy_mask(&good_mask, maskp);
> + } else
> #endif
> + {
> + slice_copy_mask(&good_mask, maskp);
> + }
You could get something nicer by removing that #ifdef and doing instead:
if (IS_ENABLED(CONFIG_PPC_64K_PAGES) && psize == MMU_PAGE_64K) {
...
} else {
slice_copy_mask(&good_mask, maskp);
}
> + slice_print_mask(" good_mask", &good_mask);
> + if (compat_maskp)
> + slice_print_mask(" compat_mask", compat_maskp);
>
> /* First check hint if it's valid or if we have MAP_FIXED */
> if (addr || fixed) {
> @@ -643,7 +634,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> #ifdef CONFIG_PPC_64K_PAGES
> if (addr == -ENOMEM && psize == MMU_PAGE_64K) {
> /* retry the search with 4k-page slices included */
> - slice_or_mask(&potential_mask, &potential_mask, &compat_mask);
> + slice_or_mask(&potential_mask, &potential_mask, compat_maskp);
> addr = slice_find_area(mm, len, &potential_mask,
> psize, topdown, high_limit);
> }
> @@ -652,17 +643,18 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> if (addr == -ENOMEM)
> return -ENOMEM;
>
> - slice_range_to_mask(addr, len, &mask);
> + slice_range_to_mask(addr, len, &potential_mask);
> slice_dbg(" found potential area at 0x%lx\n", addr);
> - slice_print_mask(" mask", &mask);
> + slice_print_mask(" mask", &potential_mask);
>
> convert:
> - slice_andnot_mask(&mask, &mask, &good_mask);
> - slice_andnot_mask(&mask, &mask, &compat_mask);
> - if (mask.low_slices ||
> - (SLICE_NUM_HIGH &&
> - !bitmap_empty(mask.high_slices, SLICE_NUM_HIGH))) {
> - slice_convert(mm, &mask, psize);
> + slice_andnot_mask(&potential_mask, &potential_mask, &good_mask);
> + if (compat_maskp && !fixed)
> + slice_andnot_mask(&potential_mask, &potential_mask, compat_maskp);
> + if (potential_mask.low_slices ||
> + (SLICE_NUM_HIGH &&
> + !bitmap_empty(potential_mask.high_slices, SLICE_NUM_HIGH))) {
> + slice_convert(mm, &potential_mask, psize);
> if (psize > MMU_PAGE_BASE)
> on_each_cpu(slice_flush_segments, mm, 1);
> }
> @@ -786,28 +778,25 @@ void slice_set_range_psize(struct mm_struct *mm, unsigned long start,
> int is_hugepage_only_range(struct mm_struct *mm, unsigned long addr,
> unsigned long len)
> {
> - struct slice_mask available;
> + const struct slice_mask *maskp;
> unsigned int psize = mm->context.user_psize;
>
> if (radix_enabled())
> return 0;
>
> - available = *slice_mask_for_size(mm, psize);
> + maskp = slice_mask_for_size(mm, psize);
> #ifdef CONFIG_PPC_64K_PAGES
> /* We need to account for 4k slices too */
> if (psize == MMU_PAGE_64K) {
> - struct slice_mask compat_mask;
> - compat_mask = *slice_mask_for_size(mm, MMU_PAGE_4K);
> - slice_or_mask(&available, &available, &compat_mask);
> + const struct slice_mask *compat_maskp;
> + struct slice_mask available;
> +
> + compat_maskp = slice_mask_for_size(mm, MMU_PAGE_4K);
> + slice_or_mask(&available, maskp, compat_maskp);
> + return !slice_check_range_fits(mm, &available, addr, len);
> }
> #endif
>
> -#if 0 /* too verbose */
> - slice_dbg("is_hugepage_only_range(mm=%p, addr=%lx, len=%lx)\n",
> - mm, addr, len);
> - slice_print_mask(" mask", &mask);
> - slice_print_mask(" available", &available);
> -#endif
That's cleanup, should be in a previous patch.
Christophe
> - return !slice_check_range_fits(mm, &available, addr, len);
> + return !slice_check_range_fits(mm, maskp, addr, len);
> }
> #endif
>
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