Function slab_free

src/foundation/slab_alloc.c:354–391

}

static void slab_free(void *ptr) {
    if (!ptr) {
        return;
    }
    uintptr_t base = (uintptr_t)ptr & SLAB_PAGE_MASK;
    slab_page_t *page = slab_map_lookup(base);
    if (!page) {
        /* Not a slab chunk → plain heap pointer (>64B or grow-fallback). */
        free(ptr);
        return;
    }

    /* It is a slab chunk. The chunk itself keeps its page alive (refcount ≥ 1)
     * until this very free, so the page cannot be freed underneath us. */
    slab_state_t *s = &tls_slab;
    slab_free_node_t *node = (slab_free_node_t *)ptr;

    if (atomic_load_explicit(&page->owner, memory_order_relaxed) == s) {
        /* Fast path: owner returns the chunk to its thread-local free list. */
        node->next = s->freelist;
        s->freelist = node;
        atomic_fetch_sub_explicit(&page->refcount, 1u, memory_order_acq_rel);
        return; /* owner guard keeps refcount ≥ 1; page is reused, not freed */
    }

    /* Foreign (or retired) free: push onto the page's lock-free MPSC stack. */
    slab_free_node_t *head = atomic_load_explicit(&page->remote_free_head, memory_order_relaxed);
    do {
        node->next = head;
    } while (!atomic_compare_exchange_weak_explicit(&page->remote_free_head, &head, node,
                                                    memory_order_release, memory_order_relaxed));
    unsigned prev = atomic_fetch_sub_explicit(&page->refcount, 1u, memory_order_acq_rel);
    if (prev == 1u) {
        /* We returned the final chunk of a retired page → release it. */
        slab_map_unregister_page(page);
        cbm_aligned_free(page);
    }
}

/* ── Page-map registration wrappers (declared after slab_map_set) ── */