On Tue, Aug 06, 2019 at 01:44:02PM +0200, Michal Hocko wrote: [snip] > > > > 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? > > > > Not at the moment with the current page idle tracking code. PageLRU(page) > > flag is checked in page_idle_get_page(). > > yes, I am aware of the current code. I strongly suspect that the PageLRU > check was there to not mark arbitrary page looked up by pfn with the > idle bit because that would be unexpected. But I might be easily wrong > here. Yes, quite possible. > > Even if we could set it for non-LRU, the idle bit (page flag) would not be > > cleared if page is not on LRU because page-reclaim code (page_referenced() I > > believe) would not clear it. > > Yes, it is either reclaim when checking references as you say but also > mark_page_accessed. I believe the later might still have the page on the > pcp LRU add cache. Maybe I am missing something something but it seems > that there is nothing fundamentally requiring the user mapped page to be > on the LRU list when seting the idle bit. > > That being said, your big hammer approach will work more reliable but if > you do not feel like changing the underlying PageLRU assumption then > document that draining should be removed longterm. Yes, at the moment I am in preference of keeping the underlying assumption same. I am Ok with adding of a comment on the drain call that it is to be removed longterm. thanks, - Joel
