Re: MPS: out-of-memory

[Pip Cet <pipcet@protonmail.com>]

On Monday, July 8th, 2024 at 18:27, Helmut Eller <eller.helmut@gmail.com> wrote:
> On Mon, Jul 08 2024, Pip Cet wrote:
> 
> > If I understood Helmut correctly, he wants a mechanism to avoid
> > thrashing after exceeding the memory limit. Maybe we need a special
> > state for that, in which we stop the GC but continue using our memory
> > while the user quits and goes to buy more RAM?
> 
> Mabye there could be a hard and a soft limit. When the soft limit
> is reached, Emacs could ask something like
> 
> There's little free memory left. Continue?
> 
> and when the hard limit is reached, it would simply abort.

I'm not sure I see the point of having two separate limits, but user preferences differ; in my case, I think it would be sufficient to stop MPS garbage collection with a message once a limit is reached, and resume it only after manual intervention. However, that's definitely a new feature rather than an existing Emacs feature we have to support...

> > Speaking of memory issues in general, I'm currently seeing pure space
> > overflows, after changes which should affect weak objects
> > exclusively. Which is really odd, because weak objects aren't
> > purecopied! Still investigating that one, but it's possible I'll just
> > give up and bump pure space.
> 
> There's a purecopy_hash_table.

Unless I messed up, it shouldn't actually purecopy weak hash tables, though. In any case, a "make bootstrap" "fixed" the problem, so I'm not sure what went wrong...

I've installed a change to die on pure space overflow if we have MPS; there's no way to tell which objects still have headers, at that point.

Pip