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

[Basile Starynkevitch <basile@starynkevitch.net>]

On 2018-04-09 07:20, ligand@free.fr wrote:
> Dear list,
> 
> Would it be possible to have automatic, region-based memory management 
> in OCaml?

Everything is possible in theory..... The real question is who would pay 
for that....
(in practice, that might mean a project of several years and several 
millions euros.... If your organization is willing to spend that, please 
tell....)

> 
> Also, would it have a better run-time performance than using the 
> current GC?
> 
> Would it completely replace the GC or would the two systems have to 
> cohabit?
> 
> I have seen even optimized OCaml programs spend 20% of their time doing 
> GC.
> I wonder if parts of those 20% could go away.


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.


-- 
Basile Starynkevitch         http://starynkevitch.net/Basile
France                       (opinions are only mine)

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