Re: New GC concept

[Daniel Colascione <dancol@dancol.org>]

On 6/7/21 10:32 AM, Matt Armstrong wrote:

> Daniel Colascione <dancol@dancol.org> writes:
>
>> Emacs has had the same GC for a decent amount of time now (since the
>> 1980s, really). I spent some time in 2020 rewriting it from scratch. I
>> haven't had time to work on the new GC recently, but I figure I'd throw
>> it out here to get some feedback on the general concept.
>>
>> Check out
>> https://github.com/dcolascione/emacs-1/blob/newgc-wip/src/alloc.c,
>> specifically the big doc comment on top
> Hey Daniel, I am no GC expert but I'm liking this a lot.  I love the
> block comments in your alloc.c -- very clear and easy to understand.
> You're in a uniquely good position to work on this.  I hope you
> continue!
Thank you!
> I'm curious about the answer to one of the unanswered questions in your
> alloc.c FAQ: What about systems without virtual memory?  Asked another
> way: can we reasonably expect to entirely replace the current GC with
> this new one?  Are there platforms Emacs supports today that would be
> left behind?

We can definitely replace the existing GC with the new GC everywhere. 
I've designed the new GC to work on systems without virtual memory 
facilities. On these systems, we'll have to run the GC in 
non-concurrent, non-generational mode, but that's no regression from 
what we have today. We'll also probably want to use a smaller block size 
on these systems to reduce fragmentation overhead.