The nature of the thing is that there's a chunk of per-architecture work required (maybe 20-30 lines of actual kernel code and another 700 lines of userspace/te

The nature of the thing is that there's a chunk of per-architecture work required (maybe 20-30 lines of actual kernel code and another 700 lines of userspace/testcase support, judging by the diffstat). What's gone in to start with includes support for x86-64, i386, powerpc and 32-bit arm as well as the common code. Maintainers of other architectures can then add support on top of this at some point. Support for new syscalls not being perfectly in sync across all kernel archs is not uncommon, I think. The other not-yet-there part is how userspace libcs are going to expose this usefully to applications; there's some interesting discussion on the kernel mailing list about that. (It needs some libc support because the kernel only supports a single registered restartable-sequence area, so if multiple libraries try to do it they'll tread on each others' feet; and libc will want to use this feature itself.)