Re: [Caml-list] Would it be possible to add automatic, region-based memory management to OCaml?

[David Teller <d.o.teller@gmail.com>]

I seem to remember that the relative performance of GC vs. manual memory
allocation depends a lot of how much additional memory the allocator can
use in addition to the memory actually allocated to the mutator (i.e.
the program). From the top of my head, even with a pretty good GC, you
need to be at ~100% additional memory for the allocator before the
performance of the GC breaks even with good manual allocation.

Now, I don't remember where this number comes from, so I could be wrong.

In addition, region-based resource management can have a number of other
benefits, such as predictable destructors, as in Rust.

There is a recent paper on extending OCalm with, basically, the Rust
ownership model by Jonathan Goodwin:
http://jondgoodwin.com/pling/gmm.pdf . In this paper, you need to
explicitly differentiate between owned data and gc-ed data, as there are
differences in both typing (owned data has affine types) and semantics
(owned data has destructors, rather than finalizers).

Cheers,
 David

On 09/04/2018 14:26, Basile Starynkevitch wrote:
> This is naive. GC is not "lost time", it is acceptable run-time overhead.
> 
> Imagine you rewrite your code in e.g. Rust or C++. Then you still need
> to allocate (and deallocate) heap memory. And that cost CPU time and
> memory overhead.
> 
> So, even if by magic you replace the GC by some region-based memory
> allocation, you won't win in practice 20%
> 
> To say it otherwise, even C malloc or C++ ::operator new have some
> measurable overhead; in some programs it is more than 20%.
> 
> In practice, Ocaml's GC is very well written and is one of the most
> competitive ones. And the GC is intimately tied to the code generator,
> so changing the GC would require significant compiler changes.
> 
> There is no silver bullet. https://en.wikipedia.org/wiki/No_Silver_Bullet
> 
> A good tutorial on GC is http://gchandbook.org/
> 
> Cheers.
> 
> 

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