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copy space: Palliate a failure mode due to fragmentation

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This commit is contained in:
Andy Wingo 2025-04-23 10:46:23 +02:00
parent 3c4fdfde0e
commit 31b373b8f2
1 changed files with 16 additions and 1 deletions
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17
src/copy-space.h
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@ -409,11 +409,23 @@ copy_space_allocator_acquire_block(struct copy_space_allocator *alloc,
return 0; return 0;
} }
static struct copy_space_block*
copy_space_obtain_empty_block_during_gc(struct copy_space *space,
const struct gc_lock *lock) {
GC_ASSERT(!copy_space_pop_empty_block(space, lock));
struct copy_space_block *block = copy_space_page_in_block(space, lock);
if (block)
atomic_fetch_add(&space->bytes_to_page_out, COPY_SPACE_BLOCK_SIZE);
return block;
}
static int static int
copy_space_allocator_acquire_empty_block(struct copy_space_allocator *alloc, copy_space_allocator_acquire_empty_block(struct copy_space_allocator *alloc,
struct copy_space *space) { struct copy_space *space) {
struct gc_lock lock = copy_space_lock(space); struct gc_lock lock = copy_space_lock(space);
struct copy_space_block *block = copy_space_pop_empty_block(space, &lock); struct copy_space_block *block = copy_space_pop_empty_block(space, &lock);
if (!block && space->in_gc)
block = copy_space_obtain_empty_block_during_gc(space, &lock);
gc_lock_release(&lock); gc_lock_release(&lock);
if (copy_space_allocator_acquire_block(alloc, block, space->active_region)) { if (copy_space_allocator_acquire_block(alloc, block, space->active_region)) {
block->in_core = 1; block->in_core = 1;
@ -925,7 +937,10 @@ static int
copy_space_init(struct copy_space *space, size_t size, uint32_t flags, copy_space_init(struct copy_space *space, size_t size, uint32_t flags,
struct gc_background_thread *thread) { struct gc_background_thread *thread) {
size = align_up(size, COPY_SPACE_BLOCK_SIZE); size = align_up(size, COPY_SPACE_BLOCK_SIZE);
size_t reserved = align_up(size, COPY_SPACE_SLAB_SIZE); // Reserve a few extra blocks to handle the fragmentation problem
// (https://wingolog.org/archives/2024/07/10/copying-collectors-with-block-structured-heaps-are-unreliable).
size_t reserved = size + COPY_SPACE_BLOCK_SIZE * 16;
reserved = align_up(reserved, COPY_SPACE_SLAB_SIZE);
if (flags & COPY_SPACE_ALIGNED) if (flags & COPY_SPACE_ALIGNED)
reserved = copy_space_round_up_power_of_two(reserved); reserved = copy_space_round_up_power_of_two(reserved);
size_t nslabs = reserved / COPY_SPACE_SLAB_SIZE; size_t nslabs = reserved / COPY_SPACE_SLAB_SIZE;