[Python-Dev] The untuned tunable parameter ARENA_SIZE

Antoine Pitrou solipsis at pitrou.net
Sun Jun 4 13:19:34 EDT 2017

On Sun, 4 Jun 2017 09:46:10 -0500
Tim Peters <tim.peters at gmail.com> wrote:
> [Tim]
> >> A virtual address space span of a terabyte could hold 1M pools, so
> >> would "only" need a 1M/8 = 128KB bit vector.  That's minor compared to
> >> a terabyte (one bit per megabyte).  
> [Antoine]
> > The virtual address space currently supported by x86-64 is 48 bits
> > wide (spanning an address space of 2**48 bytes, that is 256 TB), so you
> > would need a 2**(48-20) bits vector, i.e. 256 Mbits or 32 MB.
> >
> > Note Intel has plans to extend the virtual address space to 2**57 bytes:
> > https://www.phoronix.com/scan.php?page=news_item&px=Intel-5-Level-Paging  
> Fill in the blanks ;-)  There's only a need for the bit vector to
> cover the range of addresses _actually returned_ by the system for
> arenas allocated so far (we're only trying to identify the memory
> obmalloc _does_ control) .  I didn't spell that out, but it was
> implicit in glosses like "(or if the bit address is out of the
> vector's domain)".  That is, it's up to the bit vector implementation
> to intelligently represent what's almost always going to be a
> relatively tiny slice of a theoretically massive address space.

True.  That works if the operating system doesn't go too wild in
address space randomization, though ;-)



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