On Mon, Feb 01, 2016 at 03:24:46PM +0100, Michal Hocko wrote: > On Mon 01-02-16 16:26:08, Kirill A. Shutemov wrote: > > We don't care if there's a tail pages which is not on LRU. We are not > > going to isolate them anyway. > > yes we are not going to isolate them but calling this function on a > tail page is wrong in principle, no? PageLRU check is racy outside of > lru_lock so what if we are racing here. I know, highly unlikely but not > impossible. So I am not really sure this is an improvement. When would > we hit this VM_BUG_ON and it wouldn't be a bug or at least suspicious > usage?
Yes, there is no point in calling isolate_lru_page() for tail pages, but we do this anyway -- see the second patch. And we need to validate all drivers, that they don't forget to set VM_IO or make vma_migratable() return false in other way. Alternative approach would be to downgrate the VM_BUG_ON_PAGE() to WARN_ONCE_ON(). This way we would have chance to catch bad callers. -- Kirill A. Shutemov
