[Python-Dev] The untuned tunable parameter ARENA_SIZE
solipsis at pitrou.net
Thu Jun 1 04:52:15 EDT 2017
On Thu, 1 Jun 2017 01:41:15 -0700
Larry Hastings <larry at hastings.org> wrote:
> On 06/01/2017 01:19 AM, Antoine Pitrou wrote:
> > If you'd like to go that way anyway, I would suggest 1MB as a starting
> > point in 3.7.
> I understand the desire for caution. But I was hoping maybe we could
> experiment with 4mb in trunk for a while? We could change it to 1mb--or
> even 256k--before beta 1 if we get anxious.
Almost nobody tests "trunk" (or "master" :-)) on production systems. At
best a couple rare open source projects will run their test suite on
the pre-release betas, but that's all. So we are unlikely to spot
memory usage ballooning problems before the final release.
> >> * Many programs would be slightly faster now and then, simply because
> >> we call malloc() 1/16 as often.
> > malloc() you said? Arenas are allocated using mmap() nowadays, right?
> malloc() and free(). See _PyObject_ArenaMalloc (etc) in Objects/obmalloc.c.
_PyObject_ArenaMalloc should only be used if the OS doesn't support
mmap() or MAP_ANONYMOUS (see ARENAS_USE_MMAP). Otherwise
_PyObject_ArenaMmap is used.
Apparently OS X doesn't have MAP_ANONYMOUS but it has the synonymous
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