Zero a large memory mapping with `madvise`

Question

I have the following problem:

I allocate a large chunk of memory (multiple GiB) via mmap with MAP_ANONYMOUS. That chunk holds a large hash map w

Answer 1

On Linux, you can rely on MADV_DONTNEED on an anonymous mapping zeroing the mapping. This isn't portable, though - madvise() itself isn't standardised. posix_madvise() is standardised, but the POSIX_MADV_DONTNEED does not have the same behaviour as the Linux MADV_DONTNEED flag - posix_madvise() is always advisory, and does not affect the semantics of the application.