Re: [PATCH v3 00/12] Enable per-file/directory DAX operations V3

[Jeff Moyer]

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 reason I ask is I've had requests from application developers to do
just this.  They want to be able to switch back and forth between dax
modes.

Thanks,
Jeff

> [1] I'm beginning to think that if I type dax one more time I'm going to go
> crazy...  :-P

dax dax dax!