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 <npig...@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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