[issue45526] Set ADDRESS_BITS to 64 for obmalloc radix tree

[Łukasz Langa]

Łukasz Langa  added the comment:

Thanks, Neil! ✨  ✨

--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed
type:  -> enhancement

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[issue45526] Set ADDRESS_BITS to 64 for obmalloc radix tree

[Łukasz Langa]

Łukasz Langa  added the comment:


New changeset 0224b7180b280794b9fba62057b278ffb536c86f by Neil Schemenauer in 
branch 'main':
bpo-45526: obmalloc radix use 64 addr bits (GH-29062)
https://github.com/python/cpython/commit/0224b7180b280794b9fba62057b278ffb536c86f


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nosy: +lukasz.langa

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[issue45526] Set ADDRESS_BITS to 64 for obmalloc radix tree

[Neil Schemenauer]

Change by Neil Schemenauer :


--
keywords: +patch
pull_requests: +27329
pull_request: https://github.com/python/cpython/pull/29062

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[issue45526] Set ADDRESS_BITS to 64 for obmalloc radix tree

[Neil Schemenauer]

New submission from Neil Schemenauer :

Given this feedback:

https://github.com/python/cpython/pull/14474/files#r725488766

it is perhaps not so safe to assume that only the lower 48 bits of virtual 
addresses are significant.  I had the idea that Go made similar assumptions but 
now I'm not sure it does.  There is also a comment in this article about 
5-level page tables in Linux:

https://lwn.net/Articles/717293/
https://lwn.net/Articles/717300/

I.e. that Linux does not allocate virtual address space above 47-bit by default.

Setting ADDRESS_BITS to 64 is safer and the performance impact seems small. The 
virtual memory size of a small Python process goes up a little.  Resident set 
size doesn't significantly change.  I think the pyperformance changes are just 
noise.  The pyperformance attached file shows the 3.10 branch with ADDRESS_BITS 
set to 48 and to 64.

--
assignee: methane
files: pyperf-compare-addr-64.txt
messages: 404317
nosy: methane, nascheme
priority: normal
severity: normal
stage: patch review
status: open
title: Set ADDRESS_BITS to 64 for obmalloc radix tree
Added file: https://bugs.python.org/file50370/pyperf-compare-addr-64.txt

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