On Tue 06-08-19 06:36:27, Joel Fernandes wrote: > On Tue, Aug 06, 2019 at 10:42:03AM +0200, Michal Hocko wrote: > > On Mon 05-08-19 13:04:49, Joel Fernandes (Google) wrote: > > > This bit will be used by idle page tracking code to correctly identify > > > if a page that was swapped out was idle before it got swapped out. > > > Without this PTE bit, we lose information about if a page is idle or not > > > since the page frame gets unmapped. > > > > And why do we need that? Why cannot we simply assume all swapped out > > pages to be idle? They were certainly idle enough to be reclaimed, > > right? Or what does idle actualy mean here? > > Yes, but other than swapping, in Android a page can be forced to be swapped > out as well using the new hints that Minchan is adding? Yes and that is effectivelly making them idle, no? > Also, even if they were idle enough to be swapped, there is a chance that they > were marked as idle and *accessed* before the swapping. Due to swapping, the > "page was accessed since we last marked it as idle" information is lost. I am > able to verify this. > > Idle in this context means the same thing as in page idle tracking terms, the > page was not accessed by userspace since we last marked it as idle (using > /proc/<pid>/page_idle). Please describe a usecase and why that information might be useful. -- Michal Hocko SUSE Labs
