[macOS] active system memory is inaccurate

[giampaolo]

Recently I have often see this failure:

2024-04-17T15:58:08.9453710Z ======================================================================
2024-04-17T15:58:08.9454630Z FAIL: psutil.tests.test_osx.TestSystemAPIs.test_vmem_active
2024-04-17T15:58:08.9456300Z ----------------------------------------------------------------------
2024-04-17T15:58:08.9456970Z Traceback (most recent call last):
2024-04-17T15:58:08.9468720Z   File "/private/var/folders/c9/jqpw9nhs7jj7vm5185nyw05h0000gn/T/cibw-run-dez06mlf/cp311-macosx_x86_64/venv-test-x86_64/lib/python3.11/site-packages/psutil/tests/__init__.py", line 739, in wrapper
2024-04-17T15:58:08.9470640Z     raise exc  # noqa: PLE0704
2024-04-17T15:58:08.9471070Z     ^^^^^^^^^
2024-04-17T15:58:08.9472970Z   File "/private/var/folders/c9/jqpw9nhs7jj7vm5185nyw05h0000gn/T/cibw-run-dez06mlf/cp311-macosx_x86_64/venv-test-x86_64/lib/python3.11/site-packages/psutil/tests/__init__.py", line 731, in wrapper
2024-04-17T15:58:08.9475220Z     return fun(*args, **kwargs)
2024-04-17T15:58:08.9475660Z            ^^^^^^^^^^^^^^^^^^^^
2024-04-17T15:58:08.9476840Z   File "/Users/runner/work/psutil/psutil/psutil/tests/test_osx.py", line 154, in test_vmem_active
2024-04-17T15:58:08.9478120Z     self.assertAlmostEqual(psutil_val, vmstat_val, delta=TOLERANCE_SYS_MEM)
2024-04-17T15:58:08.9479200Z AssertionError: 2259693568 != 2308902912 within 20971520 delta (49209344 difference)

In this case the active memory reported by vm_stat is 46M bigger than what is reported by psutil. Note to self: check how either vm_stat or top calculates this.

[giampaolo]

Also free memory:

2024-04-18T06:42:07.3789370Z ======================================================================
2024-04-18T06:42:07.3789770Z FAIL: psutil.tests.test_osx.TestSystemAPIs.test_vmem_free
2024-04-18T06:42:07.3790360Z ----------------------------------------------------------------------
2024-04-18T06:42:07.3790710Z Traceback (most recent call last):
2024-04-18T06:42:07.3798740Z   File "/private/var/folders/z4/sx941vhj3jd2jb9_gwftzctc0000gn/T/cibw-run-l5yirtks/cp39-macosx_arm64/venv-test-arm64/lib/python3.9/site-packages/psutil/tests/__init__.py", line 739, in wrapper
2024-04-18T06:42:07.3799700Z     raise exc  # noqa: PLE0704
2024-04-18T06:42:07.3800720Z   File "/private/var/folders/z4/sx941vhj3jd2jb9_gwftzctc0000gn/T/cibw-run-l5yirtks/cp39-macosx_arm64/venv-test-arm64/lib/python3.9/site-packages/psutil/tests/__init__.py", line 731, in wrapper
2024-04-18T06:42:07.3801610Z     return fun(*args, **kwargs)
2024-04-18T06:42:07.3802160Z   File "/Users/runner/work/psutil/psutil/psutil/tests/test_osx.py", line 148, in test_vmem_free
2024-04-18T06:42:07.3802800Z     self.assertAlmostEqual(psutil_val, vmstat_val, delta=TOLERANCE_SYS_MEM)
2024-04-18T06:42:07.3803360Z AssertionError: 591855616 != 658292736 within 20971520 delta (66437120 difference)
2024-04-18T06:42:07.3803700Z 
2024-04-18T06:42:07.3803880Z ----------------------------------------------------------------------

[dbwiddis]

Just looked at the source code and it uses the same host_statistics64() call.

Could just be a race condition. I ran vm_stat twice on the command line (entered at the same time so minimal delay) and got variance here of 9513 pages

$ vm_stat | grep "Pages active"
vm_stat | grep "Pages active"
Pages active:                           1309272.
Pages active:                           1299759.

That's a difference in 37 MiB.

[dbwiddis]

This post is probably relevant: https://stackoverflow.com/questions/14789672/why-does-host-statistics64-return-inconsistent-results