On Tue 06-08-19 20:07:37, Minchan Kim wrote: > On Tue, Aug 06, 2019 at 12:47:55PM +0200, Michal Hocko wrote: > > 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? > > 1. mark page-A idle which was present at that time. > 2. run workload > 3. page-A is touched several times > 4. *sudden* memory pressure happen so finally page A is finally swapped out > 5. now see the page A idle - but it's incorrect.
Could you expand on what you mean by idle exactly? Why pageout doesn't really qualify as "mark-idle and reclaim"? Also could you describe a usecase where the swapout distinction really matters and it would lead to incorrect behavior? -- Michal Hocko SUSE Labs
