On Mon 01-02-16 16:38:53, Kirill A. Shutemov wrote: > 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. yes, I have seen it and that is a bug as well AFAIU. So the VM_BUG_ON triggered for the real bug. > 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. Yes, some drivers will do it incorrectly but this is VM_BUG_ON so it is usually disabled no? > 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. a ratelimitted WARN_ON would work as well. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>