I have just MFC-ed r215133 (see r215872, r215874) which changes minidump format and should result in a noticeable reduction of minidump vmcore size, especially for smaller systems. This change is for amd64 architecture only. libkvm should still support the previous version 1 minidump format. So, vmcore files produced by minidump in older kernels should be accessible by newer userland. But vmcore files produced by minidump in newer kernels will not be accessible by older userland. Which means that it's better to upgrade userland when upgrading kernel. Not sure if this information is worth an entry in UPDATING, FreeBSD isn't supposed to crash after all :-) -- Andriy Gapon