Michal Hocko <mhocko@xxxxxxxxxx> writes: > On Tue 03-03-20 09:30:28, Huang, Ying wrote: > [...] >> Yes. mmap() can control whether to populate the underlying physical >> pages. > > right because many usecases benefit from it. They simply know that the > mapping will be used completely and it is worth saving overhead for #PF. > See. there is a clear justification for that policy. > >> But for migrating MADV_FREE pages, there's no control, all pages >> will be populated again always by default. Maybe we should avoid to do >> that in some situations too. > > Now let's have a look here. It is the userspace that decided to mark > MADV_FREE pages. It is under its full control which pages are to be > freed lazily. If the userspace wants to move those pages then it is > likely aware they have been MADV_FREE, right? If the userspace wanted to > save migration overhead then it could either chose to not migrate those > pages or simply unmap them right away. So in the end we are talking > about saving munmap/MAMDV_DONTNEED or potentially more move_pages calls > to skip over MADV_FREE holes. Which is all nice but is there any > userspace that really does care? Because this is a fundamental question > here and it doesn't make much sense to discuss this left to right unless > this is clear. Although I don't agree with you, I don't want to continue. Because I feel that the discussion may be too general to go anywhere. I admit that I go to the general side firstly, sorry about that. Best Regards, Huang, Ying
