Hi, I have noticed that we have to drop caches to make the changing of S_DAX flag take effect after using chattr +x to turn on DAX for a existing regular file. The related function is xfs_diflags_to_iflags, whose second parameter determines whether we should set S_DAX immediately. I can't figure out why we do this. Is this because the page caches in address_space->i_pages are hard to deal with? I also wonder what will happen if we set S_DAX unconditionally. Thanks! Regards, Hao Li
