So, regarding the mmap, it's only used in one instance in namedb_open() and in this case NSD is using its own allocator anyway -- see region-allocator.c . IMHO, there are no advantages of using xalloc() here vs. mmap(), or actually the other way around.

But I do agree that --enable-recvmmsg should be enabled. It's actually a little surprising that they write their own implementation when this is not enabled. The setting is not enabled by enabled by default.