snawaz

Joined 6 years ago

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Jul 19

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>I don't know how to avoid heap memory allocations in haskell or make sure memory is on the stack, but both are very easy to do in C++.

Yup. I know it's easy and the default behavior in C++.

This Haskell page says, it is pretty common to allocate and deallocate memory immediately, and that GHC handles this pretty efficiently, which probably explains why Haskellers dont seem to care about this (though it seems weird to me).

https://wiki.haskell.org/GHC/Memory_Management

Comment · 6 years ago

> In the case of an image of this size you could probably just put everything on the stack.

That sounds interesting and will probably make it more efficient. But how do I put things on the stack? As per this answer on Stackoverflow, the runtime allocates memory on the heap to call functions (and probably programmers don't have any control over that?):

https://stackoverflow.com/a/5132862/415784

Comment · 6 years ago

> The runtime allocates and frees heap memory while performing local calculations.

1) If it allocates, why does `top` not show it?

2) Why does it allocate SO MUCH when it uses only a fraction? Looks like a very bad strategy to allocate 2800 times more memory than actually used?

Comment · 6 years ago

That is puzzling to me as well, particularly because `top` and `htop` on my machine don't even touch `50 MB`. That means, the first figure must be something else and I don't find a good explanation for that. I came across people who suggested to ignore that, e.g https://stackoverflow.com/questions/61666819/haskell-how-to-...

If anyone knows the exact reason for that, then please enlighten me as well. Even this otherwise awesome tutorial ignores that value: https://youtu.be/R47959rD2yw?t=1306

Comment · 6 years ago

To be fair, the Rust program isn't yet optimized fully. We tweaked few things here and there, and the speed improved from 26s to 19s. I believe it can still be improved further. I'm sure it can get better (especially if the issues in Rayon crate are addressed). However, at the same time, I think even Haskell version can be improved further. I'll update the blog post, or might create new blog post, once I have some interesting data to share.

Comment · 6 years ago

I didn't know that. I'll try that. Thanks for mentioning it.

Comment · 6 years ago

It was indeed my first Haskell program. So I'd take your comment as compliment. I have been a long time C++ programmer (https://stackoverflow.com/users/415784/nawaz), so I know what kind of tools one should look for in another language when it comes to making the code performant. So that helped me.