If you have data you don't want written to a core dump, then MAP_CONCEAL will literally only help you if that memory is in an mmap'd region. If it's in regular old virtual memory, you're fucked.

So if you're going to add a flag to something to let users conceal a region of memory from a core dump, add it to madvise, adding it to mmap is just adding arbitrary restrictions on the programmer.

Linux got it right with MADV_DONTDUMP