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reduce overhead of slot randomization

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This commit is contained in:
Daniel Micay 2018-10-30 18:09:07 -04:00
parent ceffb1a0ec
commit c29a183687
1 changed files with 15 additions and 14 deletions
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15
malloc.c
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@ -261,22 +261,22 @@ static size_t get_free_slot(struct random_state *rng, size_t slots, struct slab_
unsigned first_bitmap = random_index / 64; unsigned first_bitmap = random_index / 64;
u64 random_split = ~(~0UL << (random_index - first_bitmap * 64)); u64 random_split = ~(~0UL << (random_index - first_bitmap * 64));
for (unsigned i = first_bitmap; i <= (slots - 1) / 64; i++) { unsigned i = first_bitmap;
u64 masked = metadata->bitmap[i]; u64 masked = metadata->bitmap[i];
masked |= random_split;
for (;;) {
if (i == slots / 64) { if (i == slots / 64) {
masked |= get_mask(slots - i * 64); masked |= get_mask(slots - i * 64);
} }
if (i == first_bitmap) {
masked |= random_split;
}
if (masked != ~0UL) { if (masked != ~0UL) {
return ffzl(masked) - 1 + i * 64; return ffzl(masked) - 1 + i * 64;
} }
}
}
i = i == (slots - 1) / 64 ? 0 : i + 1;
masked = metadata->bitmap[i];
}
} else {
for (unsigned i = 0; i <= (slots - 1) / 64; i++) { for (unsigned i = 0; i <= (slots - 1) / 64; i++) {
u64 masked = metadata->bitmap[i]; u64 masked = metadata->bitmap[i];
if (i == (slots - 1) / 64) { if (i == (slots - 1) / 64) {
@ -287,6 +287,7 @@ static size_t get_free_slot(struct random_state *rng, size_t slots, struct slab_
return ffzl(masked) - 1 + i * 64; return ffzl(masked) - 1 + i * 64;
} }
} }
}
fatal_error("no zero bits"); fatal_error("no zero bits");
} }