On 17.01.20 11:17, Michal Hocko wrote: > On Fri 17-01-20 10:42:10, David Hildenbrand wrote: >> On 17.01.20 10:40, Michal Hocko wrote: >>> 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.) >>> >> >> AFAIK no device lock, no device hotplug lock, no memory hotplug lock. I >> think it holds a reference to the device and to the kernelfs node. But >> AFAIK that does not block removal of offlining/memory, just when the >> objects get freed. > > OK, so we are bug compatible after this patch ;) > :D I'm cooking something to refactor that ... nice code :) -- Thanks, David / dhildenb
