On Tue, May 11, 2021 at 3:15 PM Robert O'Callahan <roc@xxxxxxxxx> wrote: > > On Wed, May 12, 2021 at 6:12 AM Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote: > > Is some combination of bpf and kprobes a possible solution? There are > > some seemingly relevant examples here: > > https://github.com/iovisor/bpftrace/blob/master/docs/tutorial_one_liners.md > > > > I haven't tried it, but it seems like attaching to handle_userfault() > > would give similar information to perf_count_sw_page_faults, but for > > userfaults. > > That would probably work in some cases, but as Kyle said that requires > privileges and currently rr can run unprivileged (if you set > perf_event_paranoid to 1 or less) and usually does. Also, AFAIK, > kprobing handle_userfault would not be a stable ABI. True, it would not be a stable ABI. That could be solved by adding a real tracepoint, instead of just relying on a kprobe on a particular function. But, I don't think that solves the concern around permissions. I am no expert on perf_count_sw_page_faults and similar, so I'll leave it up to others to give an opinion on extending that. > > Rob
