On Tue, Feb 23, 2016 at 09:38:32PM +0300, Kirill A. Shutemov wrote: > pmd_trans_unstable(pmd), otherwise looks good: Yes sorry. > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Thanks for the quick ack, I just noticed or I would have added it to the resubmit, but it can be still added to -mm. > BTW, I guess DAX would need to introduce the same infrastructure for > pmd_devmap(). Dan? There is a i_mmap_lock_write in the truncate path that saves the day for the pmd zapping in the truncate() case without mmap_sem (the only case anon THP doesn't need to care about as truncate isn't possible in the anon case), but not in the MADV_DONTNEED madvise case that runs only with the mmap_sem for reading. The only objective of this "infrastructure" is to add no pmd_lock()ing overhead to the page fault, if the mapping is already established but not huge, and we've just to walk through the pmd to reach the pte. All because MADV_DONTNEED is running with the mmap_sem for reading unlike munmap and other slower syscalls that are forced to mangle the vmas and have to take the mmap_sem for writing regardless. The question for DAX is if it should do a pmd_devmap check inside pmd_none_or_trans_huge_or_clear_bad() after pmd_trans_huge() and get away with a one liner, or add its own infrastructure with pmd_devmap_unstable(). In the pmd_devmap case the problem isn't just in __handle_mm_fault. If it could share the same infrastructure it'd be ideal. -- 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>