[Melbourne-pm] Perl forking & Copy-on-write

Dean Hamstead dean at fragfest.com.au
Wed Jan 18 22:03:37 PST 2017

perhaps TonyC on #australia (irc.perl.org) can provide some feedback

he is seemingly perpetually working on tpf grants fixing core bugs


On 19/01/17 12:24, Mathew Robertson wrote:
> Here is an interesting read on how Python's garbage-collector, causes 
> Linux's copy-on-write, to become less effective than would otherwise:
> https://engineering.instagram.com/dismissing-python-garbage-collection-at-instagram-4dca40b29172#.25rzyh6im
> Essentially it amounts to the GC walking over Python's read-only 
> variables, but still adjusting the reference-counters... thus causing 
> Linux to see that the memory that is backing the Python instance, to 
> be written to.
> Python's cycle-detection could also cause memory-writes due to the 
> mark+sweep job.
> And it also has a generational collection, for short-term vs long-term 
> objects. Adjusting lifetime lengths, would also cause a memory-write.
> Perl also uses reference counting. So I can also see that Perl's 
> reference-counting would cause the references to be written, when a 
> given Perl variable is copied.
> The question is... does anyone have any insight into the same CoW 
> failings within the context of Perl 5 ?
> Perl 6 uses a generational collector (does it *also* use reference 
> counting?), so the generational migration would impact CoW. But given 
> the rather smart people working on that project, I can envisage that 
> some solution may eventually get implemented.
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