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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"cuda.core: a fast-path VMM grow leaves its extension unfreeable","articleBody":"## Summary\n\n`_grow_allocation_fast_path` maps a new chunk into a second, adjacent VA reservation and updates `buf._size` in place. The Buffer's deleter captured the original size when the buffer was created, so `close()` calls `deallocate(ptr, original_size)` and frees only the first reservation. The extension's reservation, mapping, and physical memory leak with no warning.\n\nNo `deallocate(ptr, size)` call can fix this: `cuMemAddressFree` frees a reservation only when `ptr` and `size` match exactly one reservation, so a range that spans two reservations cannot be freed in one call. The buffer needs to own each reservation and mapping it consists of.\n\n## Status\n\nToday the fast path is unreachable (#2388 defect 2). #2237 and #2407 make it live and would expose this leak, so they should wait for this fix. The existing fast-path test mocks the driver and cannot catch it.\n\nRefs: #2388, #2237, #2407, #2882.\n","author":{"url":"https://github.com/Andy-Jost","@type":"Person","name":"Andy-Jost"},"datePublished":"2026-09-16T21:30:35Z","url":"https://github.com/NVIDIA/cuda-python/issues/2887"}