[corona10]

• Issue: Mimalloc differences from upstream #113141

[DinoV]

https://github.com/facebookexperimental/free-threading-benchmarking/actions/runs/39860993693

[corona10]

Based on an analysis of python -c "import re", with help from a script
written with Claude and run under gdb.

The effect of reducing the page size differs by object size.

Scope	AS-IS pages	AS-IS resident	AS-IS live	AS-IS util	TO-BE pages	TO-BE resident	TO-BE live	TO-BE util
All heaps	149	5480 KiB	4106 KiB	75 %	309	4964 KiB	4102 KiB	83 %
MEM	46	1668 KiB	1146 KiB	69 %	77	1420 KiB	1142 KiB	80 %
OBJECT	45	1604 KiB	1083 KiB	68 %	88	1344 KiB	1083 KiB	81 %
GC	47	2108 KiB	1841 KiB	87 %	133	2088 KiB	1841 KiB	88 %
GC_PRE	11	100 KiB	35 KiB	35 %	11	112 KiB	35 KiB	32 %
<=256 B	68	2540 KiB	2228 KiB	88 %	174	2556 KiB	2228 KiB	87 %
256 B-2 KiB	47	1636 KiB	1346 KiB	82 %	109	1608 KiB	1346 KiB	84 %
2-64 KiB	30	1088 KiB	315 KiB	29 %	22	584 KiB	311 KiB	53 %
>64 KiB	4	216 KiB	216 KiB	100 %	4	216 KiB	216 KiB	100 %

[corona10]

cc @nascheme

[corona10]

@DinoV @nascheme @mpage
According to the benchmark results, this change reduces memory usage by 3% compared to the baseline, with no performance regression. Although there is no comparison with the default build, the results do confirm a reduction in memory usage.

[corona10]

cc @daanx

[corona10]

We may need to tune a 32-bit system, but I prefer to pass at this time.