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gh-112532: Tag mimalloc heaps and pages (#113742)

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* gh-112532: Tag mimalloc heaps and pages

Mimalloc pages are data structures that contain contiguous allocations
of the same block size. Note that they are distinct from operating
system pages. Mimalloc pages are contained in segments.

When a thread exits, it abandons any segments and contained pages that
have live allocations. These segments and pages may be later reclaimed
by another thread. To support GC and certain thread-safety guarantees in
free-threaded builds, we want pages to only be reclaimed by the
corresponding heap in the claimant thread. For example, we want pages
containing GC objects to only be claimed by GC heaps.

This allows heaps and pages to be tagged with an integer tag that is
used to ensure that abandoned pages are only claimed by heaps with the
same tag. Heaps can be initialized with a tag (0-15); any page allocated
by that heap copies the corresponding tag.

* Fix conversion warning
This commit is contained in:
Sam Gross 2024-01-05 15:08:50 -05:00 • committed by GitHub
parent eb53750757
commit 0b7476080b
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7 changed files with 35 additions and 16 deletions
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14
Objects/mimalloc/heap.c
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@ -209,7 +209,7 @@ mi_heap_t* mi_heap_get_backing(void) {
return bheap;
}
void _mi_heap_init_ex(mi_heap_t* heap, mi_tld_t* tld, mi_arena_id_t arena_id)
void _mi_heap_init_ex(mi_heap_t* heap, mi_tld_t* tld, mi_arena_id_t arena_id, bool no_reclaim, uint8_t tag)
{
_mi_memcpy_aligned(heap, &_mi_heap_empty, sizeof(mi_heap_t));
heap->tld = tld;
@ -224,17 +224,19 @@ void _mi_heap_init_ex(mi_heap_t* heap, mi_tld_t* tld, mi_arena_id_t arena_id)
heap->cookie = _mi_heap_random_next(heap) | 1;
heap->keys[0] = _mi_heap_random_next(heap);
heap->keys[1] = _mi_heap_random_next(heap);
heap->no_reclaim = no_reclaim;
heap->tag = tag;
// push on the thread local heaps list
heap->next = heap->tld->heaps;
heap->tld->heaps = heap;
}
mi_decl_nodiscard mi_heap_t* mi_heap_new_in_arena(mi_arena_id_t arena_id) {
mi_heap_t* bheap = mi_heap_get_backing();
mi_heap_t* heap = mi_heap_malloc_tp(bheap, mi_heap_t); // todo: OS allocate in secure mode?
if (heap == NULL) return NULL;
_mi_heap_init_ex(heap, bheap->tld, arena_id);
heap->no_reclaim = true; // don't reclaim abandoned pages or otherwise destroy is unsafe
// push on the thread local heaps list
heap->next = heap->tld->heaps;
heap->tld->heaps = heap;
// don't reclaim abandoned pages or otherwise destroy is unsafe
_mi_heap_init_ex(heap, bheap->tld, arena_id, true, 0);
return heap;
}