On Tue, Jul 23, 2024 at 6:11 PM James Houghton <jthoughton@xxxxxxxxxx> wrote: > > Replace the MMU write locks (taken in the memslot iteration loop) for > read locks. > > Grabbing the read lock instead of the write lock is safe because the > only requirement we have is that the stage-2 page tables do not get > deallocated while we are walking them. The stage2_age_walker() callback > is safe to race with itself; update the comment to reflect the > synchronization change. > > Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx> > --- Here is some data to show that this patch at least *can* be helpful: # arm64 patched to do aging (i.e., set HAVE_KVM_MMU_NOTIFIER_YOUNG_FAST_ONLY) # The test is faulting memory in while doing aging as fast as possible. # taskset -c 0-32 ./access_tracking_perf_test -l -r /dev/cgroup/memory -p -v 32 -m 3 # Write lock vcpu wall time : 3.039207157s lru_gen avg pass duration : 1.660541541s, (passes:2, total:3.321083083s) # Read lock vcpu wall time : 3.010848445s lru_gen avg pass duration : 0.306623698s, (passes:11, total:3.372860688s) Aging is able to run significantly faster, but vCPU runtime isn't affected much (in this test). It would be really nice to motivate this patch with a test that didn't require patching the kernel... Oliver and Marc, please let me know if you'd like to see more data. I'm also happy to simply drop this patch.
