Kernel prepatch 5.16-rc5

Do give it a good testing - with the holidays coming up, things are probably going to slow down both on the development and testing front, and as a result I expect that I will also extend the rc series by another week not because it's necessarily needed (too early to tell, but doesn't feel that way), but simply because nobody will want to open the next merge window immediately in the new year.

One small change of note in this -rc is that the default limit for the number of pages that can be locked into memory by an unprivileged process has been raised to 8MB; see this article for a summary of the discussions leading up to this change.