On Tue 06-08-19 06:45:54, Joel Fernandes wrote: > On Tue, Aug 06, 2019 at 10:43:57AM +0200, Michal Hocko wrote: > > On Mon 05-08-19 13:04:50, Joel Fernandes (Google) wrote: > > > During idle tracking, we see that sometimes faulted anon pages are in > > > pagevec but are not drained to LRU. Idle tracking considers pages only > > > on LRU. Drain all CPU's LRU before starting idle tracking. > > > > Please expand on why does this matter enough to introduce a potentially > > expensinve draining which has to schedule a work on each CPU and wait > > for them to finish. > > Sure, I can expand. I am able to find multiple issues involving this. One > issue looks like idle tracking is completely broken. It shows up in my > testing as if a page that is marked as idle is always "accessed" -- because > it was never marked as idle (due to not draining of pagevec). > > The other issue shows up as a failure in my "swap test", with the following > sequence: > 1. Allocate some pages > 2. Write to them > 3. Mark them as idle <--- fails > 4. Introduce some memory pressure to induce swapping. > 5. Check the swap bit I introduced in this series. <--- fails to set idle > bit in swap PTE. > > Draining the pagevec in advance fixes both of these issues. This belongs to the changelog. > This operation even if expensive is only done once during the access of the > page_idle file. Did you have a better fix in mind? Can we set the idle bit also for non-lru pages as long as they are reachable via pte? -- Michal Hocko SUSE Labs
