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Low Overhead Allocation Sampling in a Garbage Collected Virtual Machine

Low Overhead Allocation Sampling in a Garbage Collected Virtual Machine

2 comments

·June 23, 2025
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finnh

> Enabling allocation sampling profiling with a sampling period of 4 MB leads to a maximum time overhead of 25% in our benchmarks, over un-profiled regular execution

25% is not low overhead, but perhaps this example is the worse case and other tunings actually are low overhead. There's no exact definition I don't think, but anything much over 3% starts to feel like a lot of overhead to me.

Reading on:

> Our main technical insight is that the check whether an allocation should be sampled can be made free. This is done by folding it into the bump-pointer allocator check that PyPy’s GC uses to find out if it should start a minor collection. In this way the fast path with and without memory sampling are exactly the same.

That is cool, and means you only pay for the samples you produce = something you could leave enabled confidently, with a low-enough sample rate at least.

randomNumber7

Just use Rust then you don't need a garbage collector /S