Ira Weiny <ira.weiny@xxxxxxxxx> writes: > On Fri, Feb 14, 2020 at 04:23:19PM -0500, Jeff Moyer wrote: >> Ira Weiny <ira.weiny@xxxxxxxxx> writes: >> >> > [disclaimer: the following assumes the underlying 'device' (superblock) >> > supports DAX] >> > >> > ... which results in S_DAX == false when the file is opened without the mount >> > option. The key would be that all directories/files created under a root with >> > XFS_DIFLAG2_DAX == true would inherit their flag and be XFS_DIFLAG2_DAX == true >> > all the way down the tree. Any file not wanting DAX would need to set >> > XFS_DIFLAG2_DAX == false. And setting false could be used on a directory to >> > allow a user or group to not use dax on files in that sub-tree. >> > >> > Then without '-o dax' (XFS_MOUNT_DAX == false) all files when opened set S_DAX >> > equal to XFS_DIFLAG2_DAX value. (Directories, as of V4, never get S_DAX set.) >> > >> > If '-o dax' (XFS_MOUNT_DAX == true) then S_DAX is set on all files. >> >> One more clarifying question. Let's say I set XFS_DIFLAG2_DAX on an >> inode. I then open the file, and perform mmap/load/store/etc. I close >> the file, and I unset XFS_DIFLAG2_DAX. Will the next open treat the >> file as S_DAX or not? My guess is the inode won't be evicted, and so >> S_DAX will remain set. > > The inode will not be evicted, or even it happens to be xfs_io will reload it > to unset the XFS_DIFLAG2_DAX flag. And the S_DAX flag changes _with_ the > XFS_DIFLAG2_DAX change when it can (when the underlying storage supports > S_DAX). OK, so it will be possible to change the effective mode. I'll try to get some testing in on this series, now. Thanks! Jeff
