On Tue, May 03, 2022 at 03:15:24AM +0200, David Hildenbrand wrote: > > >>>> However, I assume we have the same issue right now already with > >> ZONE_MOVABLE and MIGRATE_CMA when trying to pin a page residing on these > > > > ZONE_MOVALBE is also changed dynamically? > > > > Sorry, with "same issue" I meant failing to pin if having to migrate and > the page is temporarily unmovable. > > >> there are temporarily unmovable and we fail to migrate. But it would now > >> apply even without ZONE_MOVABLE or MIGRATE_CMA. Hm... > > > > Didn't parse your last mention. > > On a system that neither uses ZONE_MOVABLE nor MIGRATE_CMA we might have > to migrate now when pinning. I don't understand your point. My problem is pin_user_pages with FOLL_LONGTERM. It shouldn't pin a page from ZONE_MOVABLE and cma area without migrating page out of movable zone or CMA area. That's why try_grab_folio checks whether target page stays in those movable areas. However, to check CMA area, is_migrate_cma_page is racy so the FOLL_LONGTERM flag semantic is broken right now. Do you see any problem of the fix? A thing to get some attention is whether we need READ_ONCE or not for the local variable mt.
