On Fri 17-01-20 10:25:06, David Hildenbrand wrote: > On 17.01.20 09:59, Michal Hocko wrote: > > On Fri 17-01-20 09:51:05, David Hildenbrand wrote: > >> On 17.01.20 03:21, Qian Cai wrote: > > [...] > >>> Even though has_unmovable_pages doesn't hold any reference to the > >>> returned page this should be reasonably safe for the purpose of > >>> reporting the page (dump_page) because it cannot be hotremoved. The > >> > >> This is only true in the context of memory unplug, but not in the > >> context of is_mem_section_removable()-> is_pageblock_removable_nolock(). > > > > Well, the above should hold for that path as well AFAICS. If the page is > > unmovable then a racing hotplug cannot remove it, right? Or do you > > consider a temporary unmovability to be a problem? > > Somebody could test /sys/devices/system/memory/memoryX/removable. While > returning the unmovable page, it could become movable and > offlining+removing could succeed. Doesn't this path use device lock or something? If not than the new code is not more racy then the existing one. Just look at is_pageblock_removable_nolock and how it dereferences struct page (page_zonenum in page_zone.) -- Michal Hocko SUSE Labs
