Re: [PATCH 08/10] powerpc/mm/slice: Use const pointers to cached slice masks where possible

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@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);
+	}

+	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