[RFC REBASED 3/5] powerpc/mm/slice: implement slice_check_range_fits

From: Christophe Leroy
Date: Mon Feb 12 2018 - 13:13:49 EST


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.

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/mm/slice.c | 68 ++++++++++++++++++++++++++-----------------------
1 file changed, 36 insertions(+), 32 deletions(-)

diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index ddf015d2d05b..311168ca3939 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c
@@ -233,22 +233,36 @@ static const struct slice_mask *slice_mask_for_size(struct mm_struct *mm, int ps
#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 (start < SLICE_LOW_TOP) {
+ unsigned long mend = min(end,
+ (unsigned long)(SLICE_LOW_TOP - 1));
+
+ low_slices = (1u << (GET_LOW_SLICE_INDEX(mend) + 1))
+ - (1u << GET_LOW_SLICE_INDEX(start));
+ }
+ if ((low_slices & available->low_slices) != low_slices)
+ return false;
+
+ if ((start + len) > SLICE_LOW_TOP) {
+ unsigned long start_index = GET_HIGH_SLICE_INDEX(start);
+ unsigned long align_end = ALIGN(end, (1UL << SLICE_HIGH_SHIFT));
+ unsigned long count = GET_HIGH_SLICE_INDEX(align_end) - start_index;
+ unsigned long i;

- slice_bitmap_and(result, mask->high_slices, available->high_slices,
- slice_count);
+ for (i = start_index; i < start_index + count; i++) {
+ if (!test_bit(i, available->high_slices))
+ return false;
+ }
+ }

- return (mask->low_slices & available->low_slices) == mask->low_slices &&
- slice_bitmap_equal(result, mask->high_slices, slice_count);
+ return true;
}

static void slice_flush_segments(void *parm)
@@ -519,12 +533,6 @@ 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;
- slice_bitmap_zero(mask.high_slices, SLICE_NUM_HIGH);
-
/* silence stupid warning */;
potential_mask.low_slices = 0;
slice_bitmap_zero(potential_mask.high_slices, SLICE_NUM_HIGH);
@@ -586,15 +594,11 @@ 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;
}
@@ -620,10 +624,11 @@ 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 */
@@ -829,13 +834,12 @@ 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 */
@@ -852,6 +856,6 @@ 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
--
2.13.3