[petsc-dev] Using multiple mallocs with PETSc

[Jed Brown]

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?

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.
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