Michal Hocko <mhocko@xxxxxxxx> writes: > On Fri 16-04-21 07:26:43, Dave Hansen wrote: >> On 4/16/21 5:35 AM, Michal Hocko wrote: >> > - Anonymous pages are bit tricky because they can be demoted even when >> > they cannot be reclaimed due to no (or no available) swap storage. >> > Unless I have missed something the second round will try to reclaim >> > them even the later is true and I am not sure this is completely OK. >> >> What we want is something like this: >> >> Swap Space / Demotion OK -> Can Reclaim >> Swap Space / Demotion Off -> Can Reclaim >> Swap Full / Demotion OK -> Can Reclaim >> Swap Full / Demotion Off -> No Reclaim >> >> I *think* that's what can_reclaim_anon_pages() ends up doing. Maybe I'm >> misunderstanding what you are referring to, though. By "second round" >> did you mean when we do reclaim on a node which is a terminal node? > > No, I mean the migration failure case where you splice back to the page > list to reclaim. In that round you do not demote and want to reclaim. > But a lack of swap space will make that page unreclaimable. I suspect > this would just work out fine but I am not sure from the top of my head. I have tested this via injecting some migration errors (returning 0 from demote_page_list() before migration) on a system without swap. The system can still work properly. In ftrace, I can find add_to_swap() are called much more times, and it can deal with the situation where the swap space isn't available. Best Regards, Huang, Ying
