gh-153568: Pause the GC while converting the AST to Python objects#153583
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pablogsal wants to merge 1 commit into
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gh-153568: Pause the GC while converting the AST to Python objects#153583pablogsal wants to merge 1 commit into
pablogsal wants to merge 1 commit into
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Freshly converted AST nodes cannot be part of a reference cycle yet, so collections during the conversion only pay to traverse the half-built tree without ever freeing any of it.
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Building the Python object tree out of the C AST allocates thousands of container objects in a burst, which repeatedly trips the garbage collector into traversing the half-built tree. Those nodes cannot be part of a reference cycle until the conversion exposes them, so a collection during the conversion can never free anything of this tree. Pausing the collector around the conversion (restoring the previous state, so a user-disabled GC stays disabled) removes those wasted traversals.
Benchmark (running
ast.parseover 8 of the largest stdlib files, 1.3 MB, 20 times per run; pinned cores):Executed instructions (stable under machine load,
perf stat) drop by 5.6%.