On Fri, 17 Apr 2020 13:16:29 +0100 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > 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. Good point. But, isn't it ok to use Accessed bit as long as PG_Idle and PG_Young is adjusted properly? Current DAMON implementation does so, as idle_page_tracking also does. That said, the core logics of DAMON and the underlying access check primitive are logically seperated. I am planning[1] to further entirely seperate those and let users to be able to use right access check promitive for their needs. If I'm missing something, please let me know. [1] https://lore.kernel.org/linux-mm/20200409094232.29680-1-sjpark@xxxxxxxxxx/ Thanks, SeongJae Park > > -- > Mel Gorman > SUSE Labs
