bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. by markshannon · Pull Request #29879 · python/cpython · GitHub

Produces a solid 1% speedup
See faster-cpython/ideas#80 for full discussion.

https://bugs.python.org/issue45947

…s and plain Python objects. Work in progress.

…ters.

… classes.

🤖 New build scheduled with the buildbot fleet by @markshannon for commit 79e61bf 🤖

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🤖 New build scheduled with the buildbot fleet by @markshannon for commit ce0f65b 🤖

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_PyObject_GC_Malloc is part of stable ABI. AFAIK the function cannot be removed.

It's not part of the stable ABI. It starts with an underscore.
https://www.python.org/dev/peps/pep-0384/#excluded-functions

Misc/stable_abi.txt define it as stable ABI.

function _PyObject_GC_Malloc
    added 3.2
    abi_only

On the other hand, no public macro in Python/C API use it. So I doubt it is actually stable abi.

As far as this repo, only one package in top4000 packages uses it.
https://github.com/hpyproject/top4000-pypi-packages/search?q=_PyObject_GC_Malloc

I sent an email to python-dev asking for clarification of the status of this functions and others that start with _ but are listed in Misc/stable_abi.txt. (It is not listed in Doc/data/stable_abi.dat.)

Here's a first pass at a review, mostly nits. I think I'm following everything, though I'm not necessarily fully aware of the whole big picture.

I sent an email to python-dev asking for clarification of the status of this functions and others that start with _ but are listed in Misc/stable_abi.txt. (It is not listed in Doc/data/stable_abi.dat.)

Wow, you can use & on pointers. I didn't know that. :-)

Only after you've cast it to an int. You can do anything with a cast 🙂
NULL is usually just 0 cast to a pointer, after all.

Oh, somehow I thought uintptr_t was a pointer. :-/

Please realign these like the rest?

I'm guessing that if we have a class of objects and only some of those have a materialized __dict__ that will wreak havoc with our specialization, right? Because it will flop-flop as it encounters instances with and without __dict__. In this case we have to hope that the vast majority don't have a __dict__.

Yes.
The specialized case is so much faster though, that it might not be any worse than not specializing at all, even in that case.

LGTM.

python/cpython#29879 changed the layout of user classes, and the code is no longer able to find the location of __dict__. Do a quick fix for now, as we don't support pretty-printing user defined classes.

markshannon added 12 commits August 5, 2021 12:06

Remove unsafe _PyObject_GC_Calloc function.

ee59772

Place __dict__ immediately before GC header for variable sized object…

72b71cc

…s and plain Python objects. Work in progress.

Restore documented behavior of tp_dictoffset.

cd22dac

Merge branch 'main' into regular-dict-placement

4c83f77

Fix up lazy dict creation logic to use managed dict pointers.

8a8593c

Manage values pointer, placing them directly before managed dict poin…

34b5cea

…ters.

Refactor a bit.

e8c74ab

Fix specialization of managed values.

1bf13b0

Convert hint-based load/store attr specialization target managed dict…

a025dfb

… classes.

Specialize LOAD_METHOD for managed dict objects.

5a012a8

Merge branch 'main' into regular-dict-placement

e7734b8

Use newer API internally.

14d41ab

markshannon requested review from methane and pablogsal as code owners December 1, 2021 14:04

the-knights-who-say-ni added the CLA signed label Dec 1, 2021

bedevere-bot added the awaiting core review label Dec 1, 2021

markshannon added 2 commits December 1, 2021 14:06

Add NEWS.

123171a

Use inline functions instead of magic constants.

48d6a58

markshannon requested a review from a team as a code owner December 1, 2021 16:59

Remove unsafe _PyObject_GC_Malloc() function.

79e61bf

markshannon force-pushed the regular-dict-placement branch from a76861c to 79e61bf Compare December 1, 2021 17:04

markshannon added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Dec 2, 2021

bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Dec 2, 2021

Remove invalid assert.

ce0f65b

markshannon added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Dec 2, 2021

bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Dec 2, 2021

tiran reviewed Dec 2, 2021

View reviewed changes

Add comment explaning use of Py_TPFLAGS_MANAGED_DICT.

98ddaed

gvanrossum self-requested a review December 6, 2021 18:10

gvanrossum approved these changes Dec 6, 2021

View reviewed changes

bedevere-bot added awaiting merge and removed awaiting core review labels Dec 6, 2021

markshannon added 4 commits December 7, 2021 11:55

Use inline function, not magic constant.

0f376b5

Tidy up struct layout a bit.

d724812

Tidy up gdb/libpython.py.

9435bae

Fix whitespace.

302f46f

gvanrossum approved these changes Dec 7, 2021

View reviewed changes

markshannon merged commit 8319114 into python:main Dec 7, 2021

markshannon deleted the regular-dict-placement branch December 7, 2021 16:02

bedevere-bot removed the awaiting merge label Dec 7, 2021

corona10 mentioned this pull request Feb 9, 2023

gh-101430: Update tracemalloc to handle presize properly. #101745

Merged

jackyk02 mentioned this pull request Oct 21, 2023

Fix Segfault for Python 3.11 lf-lang/reactor-c#293

Merged

jackyk02 mentioned this pull request Nov 9, 2023

[Python 3.11] Fix Segfault lf-lang/reactor-c#304

Closed

malor mentioned this pull request Nov 17, 2024

cpython3.11: fix pretty-printing of UserDict, UserString, UserList malor/cpython-lldb#74

Merged

               #  define _PyGC_FINALIZED(o) PyObject_GC_IsFinalized(o)
               #endif
-              PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t size);

+              _PyObject_GC_Link(PyObject *op)
+              {
+                  PyGC_Head *g = AS_GC(op);
+                  assert(((uintptr_t)g & (sizeof(uintptr_t)-1)) == 0);  // g must be correctly aligned

		Py_TPFLAGS_MANAGED_DICT = (1 << 4)
		Py_TPFLAGS_HEAPTYPE = (1 << 9)

		else {
		if (!PyDict_CheckExact(dict)) {

bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. by markshannon · Pull Request #29879 · python/cpython · GitHub

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bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. - #29879

bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header.#29879markshannon merged 21 commits intopython:mainpython/cpython:mainfrom faster-cpython:regular-dict-placementfaster-cpython/cpython:regular-dict-placementCopy head branch name to clipboard

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bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header.#29879
markshannon merged 21 commits into
python:mainfrom
faster-cpython:regular-dict-placement

markshannon commented Dec 1, 2021 •
edited by bedevere-bot
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