Re: MPS: weak hash tables

[Andrea Corallo]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Andrea Corallo <acorallo@gnu.org> writes:
>
>> Helmut Eller <eller.helmut@gmail.com> writes:
>>
>>> On Sat, Jul 06 2024, Gerd Möllmann wrote:
>>>
>>>> Helmut, could you please see if that helps with the pi code?
>>>
>>> Yes, it helps:
>>>
>>>   ./src/emacs -Q -batch -l \
>>>   ~/.emacs.d/elpa/elisp-benchmarks-1.14/elisp-benchmarks.el --eval \
>>>   '(elisp-benchmarks-run "pidigits" nil 1)'
>>>
>>> finishes and requires 41.82 seconds compared to the 12.26 of the non-MPS
>>> version.  And it uses something like 2.8 GB compared to 350 MB of the
>>> non-MPS version (estimated by looking at the RES column in top).
>>
>> Such a difference in memory footprint is because MPS can't GC at the
>> speed the main thread is allocating or for some other reason?
>
> Yes, that's it basically. The client is allocating at a high rate,
> and not much is dying until the end of that phase.

What do you mean with "not much is dying"?  IIUC the original GC is
collecting most of them, so they are not live anymore.

> Both together mean
> that MPS is scanning like wild to make some room, without having a
> chance to find something it can discard.

Sounds to me like a bandwidth limitaiton in the collector (we see in
this patological case).