Re: Larger GC thresholds for non-interactive Emacs

[Ihor Radchenko <yantar92@gmail.com>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> The difference between the two cases is that when you have half of the
>>> heap made up of dead objects, there's a higher probability that some of
>>> those objects are clustered such that they make up a few complete
>>> 16kB blocks, whereas when only the dead objects represent only 10% of
>>> the heap, almost all 16kB blocks will contain a mis of dead and live
>>> objects and hence can't be returned to the malloc library.
>>
>> I am again confused.
>> Does what you say imply that frequent GC with small threshold is not
>> good because it will have less dead objects and have higher chance of
>> fragmentation?
>
> Not at all.  The general rule of thumb is: the sooner you recover free
> space, the better you can avoid fragmentation.

Sure. But how does the probability to get fragmentation scale with the
GC threshold? Is it linear scaling or is it nonlinear (I suspect that it
is non-linear)? Can someone quantify it? If we do, it would help to
adjust the thresholds more optimally to balance between GC time and
fragmentation.

Best,
Ihor