On Fri, Apr 17, 2020 at 12:21:29PM +0200, SeongJae Park wrote: > On Fri, 17 Apr 2020 12:04:17 +0200 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > On Fri, Apr 17, 2020 at 09:05:08AM +0200, SeongJae Park wrote: > > > I think the main idea of DAMON[1] might be able to applied here. Have you > > > considered it? > > > > > > [1] https://lore.kernel.org/linux-mm/20200406130938.14066-1-sjpark@xxxxxxxxxx/ > > > > I've ignored that entire thing after you said the information it > > provides was already available through the PMU. > > Sorry if my answer made you confused. What I wanted to say was that the > fundamental access checking mechanism that DAMON depends on is PTE Accessed bit > for now, but it could be modified to use PMU or other features instead. I would not be inclined to lean towards either approach for NUMA balancing. Fiddling with the accessed bit can have consequences for page aging and residency -- fine for debugging a problem, not to fine for normal usage. I would expect the PMU approach would have high overhead as well as taking over a PMU counter that userspace debugging may expect to be available. -- Mel Gorman SUSE Labs
