Replace malloc with mimalloc

[ammarahm-ed]

Using mimalloc instead of malloc improves performance significantly.

Pros: Improved performance with a small change

Cons: It will add an external dependency and slightly increase size of QuickJS binaries.

It has been previously added here: https://github.com/openwebf/quickjs/pull/30

Here's the benchmark I ran after replacing:

Benchmark	Master	Mimalloc	Percent Improvement
DeltaBlue	605	702	15.99%
Crypto	863	906	4.98%
RayTrace	357	963	169.33%
EarleyBoyer	682	1579	131.70%
RegExp	149	220	47.65%
Splay	736	1804	145.76%
SplayLatency	3088	4543	47.16%
NavierStokes	1511	1590	5.24%
PdfJS	2016	2949	46.21%
Mandreel	604	656	8.61%
MandreelLatency	4803	5097	6.13%
Gameboy	5191	5644	8.72%
CodeLoad	8015	13343	66.20%
Box2D	1905	2632	38.03%
Typescript	7088	9413	32.75%
Score (version 9)	1430	2060	43.98%

It could also be opt-in by the way.

[saghul]

We should do new benchmarks when considering something like this, FWIW.

[bnoordhuis]

Using a custom allocator is problematic for libquickjs.a due to:

• risk of symbol conflicts in the embedding program unless the allocator is completely namespaced off

• allocator mixup bugs (allocating with allocator A, releasing with B); maybe not a problem for quickjs but js_malloc and friends are exposed in quickjs.h

Embedders can replace the default allocator. That's something we could do in the qjs executable, although I'm in no rush to do that right now.

Tangentially, I've spotted several places where quickjs mallocs a struct that mallocs a struct that mallocs a struct. There's likely gains to be had by flattening such allocation trees.

[ammarahm-ed]

Using a custom allocator is problematic for libquickjs.a due to:

* risk of symbol conflicts in the embedding program unless the allocator is completely namespaced off

* allocator mixup bugs (allocating with allocator A, releasing with B); maybe not a problem for quickjs but js_malloc and friends _are_ exposed in quickjs.h

Embedders can replace the default allocator. That's something we could do in the qjs executable, although I'm in no rush to do that right now.

Tangentially, I've spotted several places where quickjs mallocs a struct that mallocs a struct that mallocs a struct. There's likely gains to be had by flattening such allocation trees.

1. That is understandable I think, but also solvable if there are some benefits of using a different allocator. I think mimalloc is already namespaced as mi_malloc, mi_free etc.
2. If someone uses js_malloc even now, I expect them to free with js_free and internally these apis will switch to mimalloc so if someone does end up allocating memory with malloc and then trying to free with js_free, it's on them I would say haha.

There are indeed some optimisations we could do with the default allocators too but i think the difference is just huge when using mimalloc.

[ammarahm-ed]

@saghul So I did some benchmarks with current quickjs-ng

Benchmark	Master	Mimalloc	Percent Improvement
DeltaBlue	605	702	15.99%
Crypto	863	906	4.98%
RayTrace	357	963	169.33%
EarleyBoyer	682	1579	131.70%
RegExp	149	220	47.65%
Splay	736	1804	145.76%
SplayLatency	3088	4543	47.16%
NavierStokes	1511	1590	5.24%
PdfJS	2016	2949	46.21%
Mandreel	604	656	8.61%
MandreelLatency	4803	5097	6.13%
Gameboy	5191	5644	8.72%
CodeLoad	8015	13343	66.20%
Box2D	1905	2632	38.03%
Typescript	7088	9413	32.75%
Score (version 9)	1430	2060	43.98%

[thecodrr]

That's a very significant difference. Another allocator worth trying out is jemalloc.

[RobLoach]

Perhaps as an optional dependency? Or an allocator system that lets you add a define to switch which malloc you're using?

[bnoordhuis]

Already the case:

Embedders can replace the default allocator.

[ammarahm-ed]

Even though you can replace the default allocator yourself which i have done already, making it default positions quickjs at a much better place in terms of performance for everyone and in various benchmarks. That's why i opened up this issue.

[saghul]

While having good benchmark results it would be disingenuous to do that if it turns out it's tricky to use that allocator in all situations.

That said, once I put the docs together, we can have a section where we mention things like this.

[saghul]

@ammarahm-ed I want to benchmark something semi-related to this (using calloc vs malloc + memset to be precise). How did you get the results table from your first post?