On 05.05.22 08:48, Minchan Kim wrote: > 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 Sorry for the late reply, still traveling :) Just so we're on the same page: MIGRATE_ISOLATE would be set on pageblocks that contain either free or movable pages. In case of movable pages, they are in uese. Regarding your is_cma_page() proposal, I think we might want to consider that if it really turns out to be a problem. For now, I'm fine with just documenting it. Thanks! -- Thanks, David / dhildenb
