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GeezerVison is showing github.com — gh-144319: Fix huge page leak in datastack chunk allocator by pablogsal · Pull Request #147963 · python/cpython

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@pablogsal

@pablogsal pablogsal commented Apr 1, 2026 •
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The datastack chunk allocator (allocate_chunk in pystate.c) and other
small virtual-memory users such as the JIT tracer allocate through
_PyObject_VirtualAlloc() using the logical requested size. When huge pages
are enabled, the arena allocator may round those mappings up to the platform
huge page size, so freeing with the smaller requested size can make
munmap() fail with EINVAL and leak the mapping.

This change moves the rounding logic into _PyObject_VirtualAlloc() /
_PyObject_VirtualFree() so allocation and free always agree on the full
mapped size. Keeping it in the allocator layer also avoids a hardcoded 2 MB
assumption in pystate.c and fixes the JIT tracer allocation path at the
same time.

  • Issue: Add huge pages support for pymalloc #144319

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@pablogsal
pablogsal requested review from FFY00, ZeroIntensity and ericsnowcurrently as code owners April 1, 2026 11:50
@bedevere-app bedevere-app Bot added the awaiting core review label Apr 1, 2026
@pablogsal
pablogsal requested a review from nascheme April 1, 2026 11:50
@pablogsal pablogsal changed the title Fix huge page leak in datastack chunk allocator gh-144319: Fix huge page leak in datastack chunk allocator Apr 1, 2026
@pablogsal pablogsal added the skip news label Apr 1, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Apr 1, 2026
Add huge pages support for pymalloc #144319
Open
@pablogsal pablogsal removed the skip news label Apr 1, 2026
@pablogsal
pablogsal force-pushed the fixes branch from b1a5ad8 to 9d62c27 Compare April 1, 2026 11:52
@pablogsal

pablogsal commented Apr 1, 2026

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CC: @Fidget-Spinner
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maurycy
maurycy reviewed Apr 1, 2026
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Comment thread Python/pystate.c Resolved

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maurycy
maurycy reviewed Apr 1, 2026
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Comment thread Python/pystate.c Resolved

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Comment thread Python/pystate.c Resolved

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Fidget-Spinner
Fidget-Spinner approved these changes Apr 3, 2026
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Other than the stylistic stuff @maurycy pointed out, I think this looks fine.

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Apr 3, 2026
@pablogsal
Fix huge page leak in datastack chunk allocator
b122fec 
The original fix rounded datastack chunk allocations in pystate.c so that
_PyObject_VirtualFree() would receive the full huge page mapping size.

Change direction and move that logic into _PyObject_VirtualAlloc() and
_PyObject_VirtualFree() instead. The key invariant is that munmap() must see
the full mapped size, so alloc and free now apply the same platform-specific
rounding in the allocator layer.

This keeps _PyStackChunk bookkeeping in requested-size units, avoids a
hardcoded 2 MB assumption, and also covers other small virtual-memory users
such as the JIT tracer state allocation in optimizer.c.
@pablogsal ChatGPT Codex Connector

pablogsal commented Apr 4, 2026

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I changed direction from the pystate.c-local roundup to an allocator-level fix. The important invariant here is that munmap() must always see the full mapped size, so I moved the rounding into _PyObject_VirtualAlloc() / _PyObject_VirtualFree() to keep alloc/free symmetric. That also covers the JIT tracer path instead of fixing only the datastack caller.
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@pablogsal
pablogsal force-pushed the fixes branch from 9d62c27 to b122fec Compare April 4, 2026 21:07
Fidget-Spinner
Fidget-Spinner approved these changes Apr 5, 2026
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@pablogsal
pablogsal merged commit 77fc2f5 into python:main Apr 5, 2026
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@pablogsal
pablogsal deleted the fixes branch April 5, 2026 15:29
@bedevere-app bedevere-app Bot removed the awaiting merge label Apr 5, 2026
ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
@pablogsal @ljfp
pythongh-144319: Fix huge page leak in datastack chunk allocator (pyt…
5946e83 
…hon#147963)

Fix huge page leak in datastack chunk allocator

The original fix rounded datastack chunk allocations in pystate.c so that
_PyObject_VirtualFree() would receive the full huge page mapping size.

Change direction and move that logic into _PyObject_VirtualAlloc() and
_PyObject_VirtualFree() instead. The key invariant is that munmap() must see
the full mapped size, so alloc and free now apply the same platform-specific
rounding in the allocator layer.

This keeps _PyStackChunk bookkeeping in requested-size units, avoids a
hardcoded 2 MB assumption, and also covers other small virtual-memory users
such as the JIT tracer state allocation in optimizer.c.
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Reviewers

@Fidget-Spinner Fidget-Spinner Fidget-Spinner approved these changes
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner
@ZeroIntensity ZeroIntensity Awaiting requested review from ZeroIntensity
@FFY00 FFY00 Awaiting requested review from FFY00
@nascheme nascheme Awaiting requested review from nascheme
+1 more reviewer
@maurycy maurycy maurycy left review comments
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3 participants

@pablogsal @maurycy @Fidget-Spinner
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