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0 pointstialaramex2mo ago0 comments

With Rust you always could unsafely do whatever went wrong in somebody's C or Zig or whatever, but the question is whether you would. Rust's technical design reinforces a culture where the answer is usually "No".

I don't find the claim that weird low level mmap tricks here are perf critical at all persuasive. The page recycling makes sense - I can see why that's helping performance, but the bare metal mmap calls smell to me like somebody wanted to learn about mmap and this was their excuse. Which is fine - I need to be clear about that - but it's not actually crucial to end users being happy with this software.

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vlovich1232mo ago

I think we can agree that Mitchell knows what he’s doing and isn’t playing around with mmap just because. It’s probably quite important to ensure a low memory footprint. But mmap in rust is not extra risky in some weird mystical way. It’s just a normal FFI function to get a pointer back and you can trivially build safe abstractions around it to ensure the lifetime of a slice doesn’t exceed the lifetime of the underlying map. It’s rust 101 and there’s nothing weird here that can cause the unsafe bits here to be extra dangerous (in general unsafe rust can be difficult to get right with certain constructs, but it doesn’t apply here).

tialaramexOP2mo ago

I actually don't think I agree about mmap. Reading around it seems as though Mitchell had clever ideas for abusing mmap and those didn't work out. Now he's got mmap for the pages and it works so why replace it, but that does not mean you need mmap to deliver this performance and in fact I'd be extremely surprised if that were true as somebody who spent about a decade of his life mostly writing close-to-metal database code in C using mmap...

If you want a whole lot of bytes and you ask your allocator, do you know what almost any popular general purpose allocator will do on a vaguely decent modern Unix? Call mmap to get them for you. So at most you're cutting out a few CPU instructions worth of middle man.

uecker2mo ago

Also in C or Zig you do not need to create your own memory management using mmap. Whether this is necessary in this case or not is a different question.

In the end, if the Rust advantage is that "Rust's technical design reinforces a culture" where one tries to avoid this, then this is a rather weak argument. We will see how this turns out in the long run though.

vlovich1232mo ago

The long run has already spoken. Go look at the reports out of Microsoft and Android. It’s screamingly clear that the philosophy of Rust that most code can be written in safe with small bits in unsafe is inherently safer. The defect rate plummets by one or two orders of magnitude if I recall correctly. C is an absolute failure (since it’s the baseline) and Zig has no similar adoption studies. You could argue it will be similar if you always compile releasesafe, but then performance will be worse than C or Rust due to all the checks and it’s unclear how big a while the places that aren’t dynamically checked are.

Oh and of course rust is inherently slightly faster because no reference aliasing is allowed and automatically annotated everywhere which allows for significant aggressive compiler optimizations that neither C nor Zig can do automatically and is risky to do by hand.

AndyKelley2mo ago

Microsoft and Google are on the Rust Foundation board:

https://rustfoundation.org/about/

They benefit by having more of the industry using technologies they control.

Studies from independent third parties would be less biased.

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uecker2mo ago

I don't put too much wait on the self-reporting by Microsoft or Google. I agree though that the strategy to write safe bits and abstractions is good. What I know not to be true is the idea that similar strategies would not work also in C.

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tialaramexOP2mo ago

> We will see how this turns out in the long run though.

Rust 1.0 was in 2015. This is the long run. And I disagree that safety culture is a "weak argument". It's foundational, this is where you must start, adding it afterwards is a Herculean task, so no surprise that people aren't really trying.

uecker2mo ago

I am not saying that safety culture is irrelevant, not at all. I am saying that if the advantage of Rust is the culture that emphasizes safety (or rather memory safety, if the Rust community cared about safety in general cargo would not exist in this form) then that is a weak argument.

I don't think 10 years ago there was a lot of Rust used, so I am not sure how relevant it is that 1.0 was released at this time.

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vacuity2mo ago

Of course, culture and technical design are both important for any language, but be specific. Despite the prevalence of tools that improve C's safety, writing C safely generally requires a culture of using those tools and other techniques. For better or worse, Rust's borrow checker is a clear demonstration of where Rust lies on the safety-freedom spectrum.

j / k navigate · click thread line to collapse

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vlovich1232mo ago

tialaramexOP2mo ago

uecker2mo ago

Also in C or Zig you do not need to create your own memory management using mmap. Whether this is necessary in this case or not is a different question.

vlovich1232mo ago

AndyKelley2mo ago

Microsoft and Google are on the Rust Foundation board:

https://rustfoundation.org/about/

They benefit by having more of the industry using technologies they control.

Studies from independent third parties would be less biased.

1 more reply

uecker2mo ago

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tialaramexOP2mo ago

> We will see how this turns out in the long run though.

uecker2mo ago

I don't think 10 years ago there was a lot of Rust used, so I am not sure how relevant it is that 1.0 was released at this time.

1 more reply

vacuity2mo ago

j / k navigate · click thread line to collapse