[vlovich123]

I don’t know why people still look to jemalloc. Mimalloc outperforms the standard allocator on nearly every single benchmark. Glibc’s allocator & jemalloc both are long in the tooth & don’t actually perform as well as state of the art allocators. I wish Rust would switch to mimalloc or the latest tcmalloc (not the one in gperftools).

[masklinn]

> I wish Rust would switch to mimalloc or the latest tcmalloc (not the one in gperftools).

That's nonsensical. Rust uses the system allocators for reliability, compatibility, binary bloat, maintenance burden, ..., not because they're good (they were not when Rust switched away from jemalloc, and they aren't now).

If you want to use mimalloc in your rust programs, you can just set it as global allocator same as jemalloc, that takes all of three lines: https://github.com/purpleprotocol/mimalloc_rust#usage

If you want the rust compiler to link against mimilloc rather than jemalloc, feel free to test it out and open an issue, but maybe take a gander at the previous attempt: https://github.com/rust-lang/rust/pull/103944 which died for the exact same reason the the one before that (https://github.com/rust-lang/rust/pull/92249) did: unacceptable regression of max-rss.

[vlovich123]

I know it’s easy to change but the arguments for using glibc’s allocator are less clear to me:

1. Reliability - how is an alternate allocator less reliable? Seems like a FUD-based argument. Unless by reliability you mean performance in which case yes - jemalloc isn’t reliably faster than standard allocators, but mimalloc is.

2. Compatibility - again sounds like a FUD argument. How is compatibility reduced by swapping out the allocator? You don’t even have to do it on all systems if you want. Glibc is just unequivocally bad.

3. Binary bloat - This one is maybe an OK argument although I don’t know what size difference we’re talking about for mimalloc. Also, most people aren’t writing hello world applications so the default should probably be for a good allocator. I’d also note that having a dependency of the std runtime on glibc in the first place likely bloats your binary more than the specific allocator selected.

4. Maintenance burden - I don’t really buy this argument. In both cases you’re relying on a 3rd party to maintain the code.

[masklinn]

> I know it’s easy to change but the arguments for using glibc’s allocator are less clear to me:

You can find them at the original motivation for removing jemalloc, 7 years ago: https://github.com/rust-lang/rust/issues/36963

Also it's not "glibc's allocator", it's the system allocator. If you're unhappy with glibc's, get that replaced.

> 1. Reliability - how is an alternate allocator less reliable?

Jemalloc had to be disabled on various platforms and architectures, there is no reason to think mimalloc or tcmalloc are any different.

The system allocator, while shit, is always there and functional, the project does not have to curate its availability across platforms.

> 2. Compatibility - again sounds like a FUD argument. How is compatibility reduced by swapping out the allocator?

It makes interactions with anything which does use the system allocator worse, and almost certainly fails to interact correctly with some of the more specialised system facilities (e.g. malloc.conf) or tooling (in rust, jemalloc as shipped did not work with valgrind).

> Also, most people aren’t writing hello world applications

Most people aren't writing applications bound on allocation throughput either

> so the default should probably be for a good allocator.

Probably not, no.

> I’d also note that having a dependency of the std runtime on glibc in the first place likely bloats your binary more than the specific allocator selected.

That makes no sense whatsoever. The libc is the system's and dynamically linked. And changing allocator does not magically unlink it.

> 4. Maintenance burden - I don’t really buy this argument.

It doesn't matter that you don't buy it. Having to ship, resync, debug, and curate (cf (1)) an allocator is a maintenance burden. With a system allocator, all the project does is ensure it calls the system allocators correctly, the rest is out of its purview.

[vlovich123]

The reason the reliability & compatibility arguments don’t make sense to me is that jemalloc is still in use for rustc (again - not sure why they haven’t switched to mimalloc) which has all the same platform requirements as the standard library. There’s also no reason an alternate allocator can’t be used on Linux specifically because glibc’s allocator is just bad full stop.

> It makes interactions with anything which does use the system allocator worse

That’s a really niche argument. Most people are not doing any of that and malloc.conf is only for people who are tuning the glibc allocator which is a silly thing to do when mimalloc will outperform whatever tuning you do (yes - glibc really is that bad).

> or tooling (in rust, jemalloc as shipped did not work with valgrind)

That’s a fair argument, but it’s not an unsolvable one.

> Most people aren’t writing applications bound on allocation throughput either

You’d be surprised at how big an impact the allocator can make even when you don’t think you’re bound on allocations. There’s also all sorts of other things beyond allocation throughput & glibc sucks at all of them (e.g. freeing memory, behavior in multithreaded programs, fragmentation etc etc).

> The libc is the system’s and dynamically linked. And changing allocator does not magically unlink it

I meant that the dependency on libc at all in the standard library bloats the size of a statically linked executable.

[josephg]

> jemalloc is still in use for rustc (again - not sure why they haven’t switched to mimalloc)

Performance of rustc matters a lot! If the rust compiler runs faster when using mimalloc, please benchmark & submit a patch to the compiler.

[masklinn]

I literally linked two attempts to use mimalloc in rustc just a few comments upthread.

[vlovich123]

Any links to instructions on how to run said benchmarks?

[saagarjha]

Not to mention that by using the system allocator you get all sorts of things “for free” that the system developers provide for you, wrt observability and standard tooling. This is especially true of the OS and the allocator are shipped by one group rather than being developed independently.