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The pymalloc huge page support had two problems. First, on architectures where the default huge page size exceeds the arena size (e.g. 32 MiB on PPC, 512 MiB on ARM64 with 64 KB base pages), mmap with MAP_HUGETLB silently allocates a full huge page even when the requested size is smaller. The subsequent munmap with the original arena size then fails with EINVAL, permanently leaking the entire huge page. Second, huge pages were always attempted when compiled in, with no way to disable them at runtime. On Linux, if the huge page pool is exhausted, page faults including copy-on-write faults after fork deliver SIGBUS and kill the process. The arena allocator now queries the system huge page size from /proc/meminfo and skips MAP_HUGETLB when the arena size is not a multiple of it. Huge pages also now require explicit opt-in at runtime via the PYTHON_PYMALLOC_HUGEPAGES environment variable, which is read through PyConfig and respects -E and -I flags. The config field pymalloc_hugepages is propagated to the runtime allocators struct so the low-level arena allocator can check it without calling getenv directly.
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