[petsc-dev] Using multiple mallocs with PETSc

Jeff Hammond jeff.science at gmail.com
Sun Mar 12 12:19:49 CDT 2017

On Sat, Mar 11, 2017 at 9:00 AM Jed Brown <jed at jedbrown.org> wrote:

> Jeff Hammond <jeff.science at gmail.com> writes:
> > I agree 100% that multithreaded codes that fault pages from the main
> thread in a NUMA environment are doing something wrong ;-)
> >
> > Does calloc *guarantee* pages are not mapped? If I calloc(8), do I get
> the zero page or part of the arena that's already mapped that is zeroed by
> the heap manager?
> Is your argument that calloc() should never be used in multi-threaded code?

I never use it for code that I want to behave well in a NUMA environment.

> If the allocation is larger than MMAP_THRESHOLD (128 KiB by default for
> glibc) then it calls mmap.  This obviously leaves an intermediate size
> that could be poorly mapped (assuming 4 KiB pages), but it's also so
> small that it easily fits in cache.

Is this behavior standardized or merely implementation-defined? I'm not
interested in writing code that assumes Linux/glibc.


> --
Jeff Hammond
jeff.science at gmail.com
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