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Fix thrashing of major GC when size pool is small

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If a size pooll is small, then `min_free_slots < heap_init_slots` is true.
This means that min_free_slots will be set to heap_init_slots. This
causes `swept_slots < min_free_slots` to be true in a later if statement.
The if statement could trigger a major GC which could cause major GC
thrashing.
This commit is contained in:
Peter Zhu 2022-12-20 09:06:29 -05:00
parent c72a748b27
commit 80e56d1438
Notes: git 2022-12-20 16:33:14 +00:00 
Merged: https://github.com/ruby/ruby/pull/6971
1 changed files with 12 additions and 6 deletions
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18
gc.c
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@ -5844,18 +5844,13 @@ gc_sweep_finish_size_pool(rb_objspace_t *objspace, rb_size_pool_t *size_pool)
size_t swept_slots = size_pool->freed_slots + size_pool->empty_slots;
size_t min_free_slots = (size_t)(total_slots * gc_params.heap_free_slots_min_ratio);
/* Some size pools may have very few pages (or even no pages). These size pools
* should still have allocatable pages. */
if (min_free_slots < gc_params.heap_init_slots) {
min_free_slots = gc_params.heap_init_slots;
}
/* If we don't have enough slots and we have pages on the tomb heap, move
* pages from the tomb heap to the eden heap. This may prevent page
* creation thrashing (frequently allocating and deallocting pages) and
* GC thrashing (running GC more frequently than required). */
struct heap_page *resurrected_page;
while (swept_slots < min_free_slots &&
while ((swept_slots < min_free_slots || swept_slots < gc_params.heap_init_slots) &&
(resurrected_page = heap_page_resurrect(objspace, size_pool))) {
swept_slots += resurrected_page->free_slots;
@ -5863,6 +5858,17 @@ gc_sweep_finish_size_pool(rb_objspace_t *objspace, rb_size_pool_t *size_pool)
heap_add_freepage(heap, resurrected_page);
}
/* Some size pools may have very few pages (or even no pages). These size pools
* should still have allocatable pages. */
if (min_free_slots < gc_params.heap_init_slots && swept_slots < gc_params.heap_init_slots) {
int multiple = size_pool->slot_size / BASE_SLOT_SIZE;
size_t extra_slots = gc_params.heap_init_slots - swept_slots;
size_t extend_page_count = CEILDIV(extra_slots * multiple, HEAP_PAGE_OBJ_LIMIT);
if (extend_page_count > size_pool->allocatable_pages) {
size_pool_allocatable_pages_set(objspace, size_pool, extend_page_count);
}
}
if (swept_slots < min_free_slots) {
bool grow_heap = is_full_marking(objspace);