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Reduce the size of plain Python objects from 8 to 6 machine words. #95245

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markshannon opened this issue Jul 25, 2022 · 2 comments
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Reduce the size of plain Python objects from 8 to 6 machine words. #95245

markshannon opened this issue Jul 25, 2022 · 2 comments
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pending The issue will be closed if no feedback is provided performance Performance or resource usage

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@markshannon
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markshannon commented Jul 25, 2022

Currently a plain Python object has the following fields:

  • values
  • (managed) __dict__
  • GC 1
  • GC 2
  • refcount
  • __class__
  • __weakrefs__
  • WASTED

The WASTED field is present because, due to alignment, we must allocate a multiple of 2 words.
We can reduce this to 6 by merging the values and __dict__ pointers into one (only one can be valid at any time),
and then moving the __weakrefs__ field into the empty space.

  • __weakrefs__
  • values or __dict__
  • GC 1
  • GC 2
  • refcount
  • __class__

See faster-cpython/ideas#125 for full discussion
@markshannon markshannon added the performance Performance or resource usage label Jul 25, 2022
@markshannon markshannon changed the title Reduce the size of plain objects from 8 to 6 machines words. Reduce the size of plain Python objects from 8 to 6 machine words. Jul 25, 2022
@markshannon markshannon mentioned this issue Jul 26, 2022
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markshannon added a commit that referenced this issue Aug 1, 2022
@markshannon
GH-95245: Store object values and dict pointers in single tagged poin…
de388c0 
…ter. (GH-95278)
@markshannon markshannon mentioned this issue Aug 4, 2022
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@bedevere-bot bedevere-bot mentioned this issue Aug 15, 2022
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markshannon added a commit that referenced this issue Aug 16, 2022
@markshannon
GH-95245: Move weakreflist into the pre-header. (GH-95996)
5a8c158
@bedevere-bot bedevere-bot mentioned this issue Aug 17, 2022
Merged
markshannon added a commit that referenced this issue Aug 30, 2022
@markshannon
GH-95245: Document use of MANAGED flags instead of offsets. (GH-96044)
0f733ff
@iritkatriel
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iritkatriel commented Sep 10, 2022

Is there anything left to do here?

@iritkatriel iritkatriel added the pending The issue will be closed if no feedback is provided label Sep 10, 2022
@markshannon
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markshannon commented Sep 12, 2022

Nothing more to do.

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