The pymalloc huge page support had two problems. First, onarchitectures where the default huge page size exceeds the arenasize (e.g. 32 MiB on PPC, 512 MiB on ARM64 with 64 KB basepages), mmap with MAP_HUGETLB silently allocates a full huge pageeven when the requested size is smaller. The subsequent munmapwith the original arena size then fails with EINVAL, permanentlyleaking the entire huge page. Second, huge pages were alwaysattempted when compiled in, with no way to disable them atruntime. On Linux, if the huge page pool is exhausted, pagefaults including copy-on-write faults after fork deliver SIGBUSand 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 amultiple of it. Huge pages also now require explicit opt-in atruntime 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 runtimeallocators struct so the low-level arena allocator can check itwithout calling getenv directly.

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Co-authored-by: Victor Stinner <vstinner@python.org>