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SubjectRe: [RFC REBASED 4/5] powerpc/mm/slice: Use const pointers to cached slice masks where possible
Date
Christophe Leroy <christophe.leroy@c-s.fr> writes:

> 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.
>
> This also converts the slice_mask bit operation helpers to be the usual
> 3-operand kind, which is clearer to work with. And we remove some
> unnecessary intermediate bitmaps, reducing stack and copy overhead
> further.

Can we move the reduce unncessary intermediate bitmaps as another patch?

>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> arch/powerpc/include/asm/book3s/64/slice.h | 7 +++
> arch/powerpc/include/asm/nohash/32/slice.h | 6 +++
> arch/powerpc/mm/slice.c | 77 ++++++++++++++++++------------
> 3 files changed, 59 insertions(+), 31 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/slice.h b/arch/powerpc/include/asm/book3s/64/slice.h
> index f9a2c8bd7a77..be1ce8e91ad1 100644
> --- a/arch/powerpc/include/asm/book3s/64/slice.h
> +++ b/arch/powerpc/include/asm/book3s/64/slice.h
> @@ -63,6 +63,13 @@ static inline void slice_bitmap_set(unsigned long *map, unsigned int start,
> {
> bitmap_set(map, start, nbits);
> }
> +
> +static inline void slice_bitmap_copy(unsigned long *dst,
> + const unsigned long *src,
> + unsigned int nbits)
> +{
> + bitmap_copy(dst, src, nbits);
> +}
> #endif /* __ASSEMBLY__ */
>
> #else /* CONFIG_PPC_MM_SLICES */
> diff --git a/arch/powerpc/include/asm/nohash/32/slice.h b/arch/powerpc/include/asm/nohash/32/slice.h
> index bcb4924f7d22..38f041e01a0a 100644
> --- a/arch/powerpc/include/asm/nohash/32/slice.h
> +++ b/arch/powerpc/include/asm/nohash/32/slice.h
> @@ -58,6 +58,12 @@ static inline void slice_bitmap_set(unsigned long *map, unsigned int start,
> unsigned int nbits)
> {
> }
> +
> +static inline void slice_bitmap_copy(unsigned long *dst,
> + const unsigned long *src,
> + unsigned int nbits)
> +{
> +}
> #endif /* __ASSEMBLY__ */
>
> #endif /* CONFIG_PPC_MM_SLICES */
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index 311168ca3939..b8b691369c29 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -468,21 +468,30 @@ static unsigned long slice_find_area(struct mm_struct *mm, unsigned long len,
> return slice_find_area_bottomup(mm, len, mask, psize, high_limit);
> }
>
> -static inline void slice_or_mask(struct slice_mask *dst,
> +static inline void slice_copy_mask(struct slice_mask *dst,
> const struct slice_mask *src)
> {
> - dst->low_slices |= src->low_slices;
> - slice_bitmap_or(dst->high_slices, dst->high_slices, src->high_slices,
> + dst->low_slices = src->low_slices;
> + slice_bitmap_copy(dst->high_slices, src->high_slices, SLICE_NUM_HIGH);
> +}
> +
> +static inline void slice_or_mask(struct slice_mask *dst,
> + const struct slice_mask *src1,
> + const struct slice_mask *src2)
> +{
> + dst->low_slices = src1->low_slices | src2->low_slices;
> + slice_bitmap_or(dst->high_slices, src1->high_slices, src2->high_slices,
> SLICE_NUM_HIGH);
> }
>
> static inline void slice_andnot_mask(struct slice_mask *dst,
> - const struct slice_mask *src)
> + const struct slice_mask *src1,
> + const struct slice_mask *src2)
> {
> - dst->low_slices &= ~src->low_slices;
> + dst->low_slices = src1->low_slices & ~src2->low_slices;
>
> - slice_bitmap_andnot(dst->high_slices, dst->high_slices,
> - src->high_slices, SLICE_NUM_HIGH);
> + slice_bitmap_andnot(dst->high_slices, src1->high_slices,
> + src2->high_slices, SLICE_NUM_HIGH);
> }
>
> #ifdef CONFIG_PPC_64K_PAGES
> @@ -495,10 +504,10 @@ 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;
> @@ -537,9 +546,6 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> potential_mask.low_slices = 0;
> slice_bitmap_zero(potential_mask.high_slices, SLICE_NUM_HIGH);
>
> - compat_mask.low_slices = 0;
> - slice_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);
> @@ -562,7 +568,7 @@ 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);
> + maskp = slice_mask_for_size(mm, psize);
> slice_print_mask(" good_mask", &good_mask);
>
> /*
> @@ -587,11 +593,16 @@ 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, &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);
> + }
>
> /* First check hint if it's valid or if we have MAP_FIXED */
> if (addr || fixed) {
> @@ -621,7 +632,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
> * empty and thus can be converted
> */
> slice_mask_for_free(mm, &potential_mask, high_limit);
> - slice_or_mask(&potential_mask, &good_mask);
> + slice_or_mask(&potential_mask, &potential_mask, &good_mask);
> slice_print_mask(" potential", &potential_mask);
>
> if (addr || fixed) {
> @@ -658,7 +669,7 @@ 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, &compat_mask);
> + slice_or_mask(&potential_mask, &potential_mask, compat_maskp);
> addr = slice_find_area(mm, len, &potential_mask,
> psize, topdown, high_limit);
> }
> @@ -667,16 +678,17 @@ 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);

Can we avoid reusing variables like that. I had to look at the change
below to ensure that this is intended change. The print below is wrong
then. In my patch series I did try to remove potential_mask and compat
mask and used tmp_mask in its place. IMHO that resulted in much simpiler
code. I do recompute tmp_mask for 4K size because of lack of variable.
But then i guess with your change to cache mask for different page size,
it should not have an impact?

> slice_dbg(" found potential area at 0x%lx\n", addr);
> - slice_print_mask(" mask", &mask);
> + slice_print_mask(" mask", maskp);
>
> convert:
> - slice_andnot_mask(&mask, &good_mask);
> - slice_andnot_mask(&mask, &compat_mask);
> - if (mask.low_slices ||
> - !slice_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_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);
> }
> @@ -834,19 +846,22 @@ 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, &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
>
> @@ -856,6 +871,6 @@ int is_hugepage_only_range(struct mm_struct *mm, unsigned long addr,
> slice_print_mask(" mask", &mask);
> slice_print_mask(" available", &available);
> #endif
> - return !slice_check_range_fits(mm, &available, addr, len);
> + return !slice_check_range_fits(mm, maskp, addr, len);
> }
> #endif
> --
> 2.13.3

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