Re: MPS: weak hash tables

[Gerd Möllmann]

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

> Helmut Eller <eller.helmut@gmail.com> writes:
>
>> On Sun, Jul 07 2024, Pip Cet wrote:
>>> What's going on here?
>>
>> How likely is a bug in the tree balancing code?  I find it rather odd
>> that the old GC rebalances interval trees during the sweep phase.
>
> I'd say not very likely but of course not impossible.
>
> The problem with the interval tree is that it isn't self-balancing like
> say a red-black tree. It isn't using an algorithm that I recognize.
> Already when I wrote the new redisplay code it was a problem that the
> tree sometimes degraded for which I added more calls to balance it.
>
> Both string and buffer intervals are balanced in the swepp phase of the
> old GC I see.
>
> Hm, maybe we are missing out on something here, in igc. I don't remember
> that I balance in igc.

I've also run the slow version of the test, when it happens to be slow
which is a mystery, under Instruments, which is kind of the shitty
equivalent of perf on macOS.

>From the little I see there, something I don't know is concatenating
strings, and adding text properties to them. This allocates conses and
intervals. The allocation point is running out of reserved memory,
mps_ap_fill is called, and MPS scans like mad. That's where the time
goes. Alone 13% of the whole time is spent in fix_cons for example.

More I can't see with the tools I have available here. Maybe intersting
could be that balance_intervals doesn't show up here, but that could be
due to the differences in barrier implementation on macOS.

And the good question is of course why is the test fast when invoked
like Pip showed?