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use multi-word bitmap to support up to 256 slots

This commit is contained in:
Daniel Micay 2018-10-07 13:34:52 -04:00
parent 5e2f03296e
commit cc9699f1b4
1 changed files with 49 additions and 24 deletions
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73
malloc.c
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@ -40,7 +40,7 @@ static union {
};
struct slab_metadata {
u64 bitmap;
u64 bitmap[4];
struct slab_metadata *next;
struct slab_metadata *prev;
u64 canary_value;
@ -190,15 +190,15 @@ static struct slab_metadata *alloc_metadata(struct size_class *c, size_t slab_si
}
static void set_slot(struct slab_metadata *metadata, size_t index) {
metadata->bitmap |= 1UL << index;
metadata->bitmap[index / 64] |= 1UL << index;
}
static void clear_slot(struct slab_metadata *metadata, size_t index) {
metadata->bitmap &= ~(1UL << index);
metadata->bitmap[index / 64] &= ~(1UL << index);
}
static bool get_slot(struct slab_metadata *metadata, size_t index) {
return (metadata->bitmap >> index) & 1UL;
return (metadata->bitmap[index / 64] >> index) & 1UL;
}
static u64 get_mask(size_t slots) {
@ -206,39 +206,64 @@ static u64 get_mask(size_t slots) {
}
static size_t get_free_slot(struct random_state *rng, size_t slots, struct slab_metadata *metadata) {
if (slots > 64) {
slots = 64;
}
u64 masked = metadata->bitmap | get_mask(slots);
if (masked == ~0UL) {
fatal_error("no zero bits");
}
if (SLOT_RANDOMIZE) {
// randomize start location for linear search (uniform random choice is too slow)
u64 random_split = ~(~0UL << get_random_u16_uniform(rng, slots));
unsigned random_index = get_random_u16_uniform(rng, slots);
unsigned first_bitmap = random_index / 64;
u64 random_split = ~(~0UL << (random_index - first_bitmap * 64));
size_t slot = ffzl(masked | random_split);
if (slot) {
return slot - 1;
for (unsigned i = first_bitmap; i <= slots / 64; i++) {
u64 masked = metadata->bitmap[i];
if (i == slots / 64) {
masked |= get_mask(slots - i * 64);
}
if (i == first_bitmap) {
masked |= random_split;
}
if (masked == ~0UL) {
continue;
}
return ffzl(masked) - 1 + i * 64;
}
}
for (unsigned i = 0; i <= slots / 64; i++) {
u64 masked = metadata->bitmap[i];
if (i == slots / 64) {
masked |= get_mask(slots - i * 64);
}
if (masked == ~0UL) {
continue;
}
return ffzl(masked) - 1 + i * 64;
}
return ffzl(masked) - 1;
fatal_error("no zero bits");
}
static bool has_free_slots(size_t slots, struct slab_metadata *metadata) {
if (slots > 64) {
slots = 64;
if (slots <= 64) {
u64 masked = metadata->bitmap[0] | get_mask(slots);
return masked != ~0UL;
} else if (slots <= 128) {
u64 masked = metadata->bitmap[1] | get_mask(slots - 64);
return metadata->bitmap[0] != ~0UL || masked != ~0UL;
} else if (slots <= 192) {
u64 masked = metadata->bitmap[2] | get_mask(slots - 128);
return metadata->bitmap[0] != ~0UL || metadata->bitmap[1] != ~0UL || masked != ~0UL;
}
u64 masked = metadata->bitmap | get_mask(slots);
return masked != ~0UL;
u64 masked = metadata->bitmap[3] | get_mask(slots - 192);
return metadata->bitmap[0] != ~0UL || metadata->bitmap[1] != ~0UL || metadata->bitmap[2] != ~0UL || masked != ~0UL;
}
static bool is_free_slab(struct slab_metadata *metadata) {
return !metadata->bitmap;
return !metadata->bitmap[0] && !metadata->bitmap[1] && !metadata->bitmap[2] &&
!metadata->bitmap[3];
}
static struct slab_metadata *get_metadata(struct size_class *c, void *p) {