On Tue, Aug 13, 2019 at 05:04:50PM +0200, Michal Hocko wrote: > On Wed 07-08-19 13:15:55, Joel Fernandes (Google) wrote: > > Idle page tracking currently does not work well in the following > > scenario: > > 1. mark page-A idle which was present at that time. > > 2. run workload > > 3. page-A is not touched by workload > > 4. *sudden* memory pressure happen so finally page A is finally swapped out > > 5. now see the page A - it appears as if it was accessed (pte unmapped > > so idle bit not set in output) - but it's incorrect. > > > > To fix this, we store the idle information into a new idle bit of the > > swap PTE during swapping of anonymous pages. > > > > Also in the future, madvise extensions will allow a system process > > manager (like Android's ActivityManager) to swap pages out of a process > > that it knows will be cold. To an external process like a heap profiler > > that is doing idle tracking on another process, this procedure will > > interfere with the idle page tracking similar to the above steps. > > This could be solved by checking the !present/swapped out pages > right? Whoever decided to put the page out to the swap just made it > idle effectively. So the monitor can make some educated guess for > tracking. If that is fundamentally not possible then please describe > why. But the monitoring process (profiler) does not have control over the 'whoever made it effectively idle' process. As you said it will be a guess, it will not be accurate. I am curious what is your concern with using a bit in the swap PTE? (Adding Konstantin as well since we may be interested in this, since we also suggested this idea). thanks, - Joel
