Re: [PATCH 06/10] powerpc/mm/slice: implement slice_check_range_fits

Rather than build slice masks from a range then use that to check for
fit in a candidate mask, implement slice_check_range_fits that checks
if a range fits in a mask directly.

This allows several structures to be removed from stacks, and also we
don't expect a huge range in a lot of these cases, so building and
comparing a full mask is going to be more expensive than testing just
one or two bits of the range.

On POWER8, this increases vfork+exec+exit performance by 0.3%
and reduces time to mmap+munmap a 64kB page by 5%.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
  arch/powerpc/mm/slice.c | 63 ++++++++++++++++++++++++++-----------------------
  1 file changed, 34 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index 2115efe5e869..3841fca75006 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c

@@ -179,26 +179,35 @@ static struct slice_mask *slice_mask_for_size(struct mm_struct *mm, int psize)
  #error "Must define the slice masks for page sizes supported by the platform"
  #endif
  
-static int slice_check_fit(struct mm_struct *mm,
-			   const struct slice_mask *mask,
-			   const struct slice_mask *available)
+static bool slice_check_range_fits(struct mm_struct *mm,
+			   const struct slice_mask *available,
+			   unsigned long start, unsigned long len)
  {
-	DECLARE_BITMAP(result, SLICE_NUM_HIGH);
-	/*
-	 * Make sure we just do bit compare only to the max
-	 * addr limit and not the full bit map size.
-	 */
-	unsigned long slice_count = GET_HIGH_SLICE_INDEX(mm->context.slb_addr_limit);
+	unsigned long end = start + len - 1;
+	u64 low_slices = 0;
  
-	if (!SLICE_NUM_HIGH)
-		return (mask->low_slices & available->low_slices) ==
-		       mask->low_slices;
+	if (start < SLICE_LOW_TOP) {
+		unsigned long mend = min(end, (SLICE_LOW_TOP - 1));

+	}
  
-	return (mask->low_slices & available->low_slices) == mask->low_slices &&
-		bitmap_equal(result, mask->high_slices, slice_count);
+	return true;
  }
  
  static void slice_flush_segments(void *parm)

@@ -562,15 +571,11 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
  #endif
  
  	/* First check hint if it's valid or if we have MAP_FIXED */
-	if (addr != 0 || fixed) {
-		/* Build a mask for the requested range */
-		slice_range_to_mask(addr, len, &mask);
-		slice_print_mask(" mask", &mask);
-
+	if (addr || fixed) {

  		/* Check if we fit in the good mask. If we do, we just return,
  		 * nothing else to do
  		 */
-		if (slice_check_fit(mm, &mask, &good_mask)) {
+		if (slice_check_range_fits(mm, &good_mask, addr, len)) {
  			slice_dbg(" fits good !\n");
  			return addr;
  		}

@@ -596,10 +601,11 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
  	slice_or_mask(&potential_mask, &good_mask);
  	slice_print_mask(" potential", &potential_mask);
  
-	if ((addr != 0 || fixed) &&
-			slice_check_fit(mm, &mask, &potential_mask)) {
-		slice_dbg(" fits potential !\n");
-		goto convert;
+	if (addr || fixed) {
+		if (slice_check_range_fits(mm, &potential_mask, addr, len)) {
+			slice_dbg(" fits potential !\n");
+			goto convert;
+		}

  	}
  
  	/* If we have MAP_FIXED and failed the above steps, then error out */

@@ -772,13 +778,12 @@ 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 mask, available;
+	struct slice_mask available;
  	unsigned int psize = mm->context.user_psize;
  
  	if (radix_enabled())
  		return 0;
  
-	slice_range_to_mask(addr, len, &mask);
  	available = *slice_mask_for_size(mm, psize);
  #ifdef CONFIG_PPC_64K_PAGES
  	/* We need to account for 4k slices too */

@@ -795,6 +800,6 @@ 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_fit(mm, &mask, &available);
+	return !slice_check_range_fits(mm, &available, addr, len);
  }
  #endif