On Tue, Aug 06, 2019 at 01:14:52PM +0200, Michal Hocko wrote: > 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, Did you read this post ? : https://lore.kernel.org/lkml/20190806104715.GC218260@xxxxxxxxxx/T/#m4ece68ceaf6e54d4d29e974f5f4c1080e733f6c1 Just wanted to be sure you did not miss it. thanks, - Joel
