On Wed, May 04, 2022 at 03:48:54PM -0700, Minchan Kim wrote: > On Tue, May 03, 2022 at 06:02:33PM +0200, David Hildenbrand wrote: > > On 03.05.22 17:26, Minchan Kim wrote: > > > 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? > > > > My point is that you might decide to migrate a page because you stumble > > over MIGRATE_ISOLATE, although there is no need to reject long-term > > pinning and to trigger page migration. > > > > Assume a system without ZONE_MOVABLE and without MIGRATE_CMA. Assume > > someone reserves gigantic pages (alloc_contig_range()) and you have > > concurrent long-term pinning on a page that is no MIGRATE_ISOLATE. > > > > GUP would see MIGRATE_ISOLATE and would reject pinning. The page has to > > be migrated, which can fail if the page is temporarily unmovable. > > A dump question since I'm not familiar with hugetlb. > > Is above reasonable scenario? > > The gigantic page is about to be created using alloc_contig_range so > they has MIGRATE_ISOLATE as temporal state. It means no one uses the > page yet so I guess the page is not mapped at userspace but other is > trying to access the page using pin_user_pages? > Too dump question. Never mind. Posted v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@xxxxxxxxxx/T/#u Thanks.
