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Diffstat (limited to 'Documentation/filesystems/dax.rst')
| -rw-r--r-- | Documentation/filesystems/dax.rst | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/Documentation/filesystems/dax.rst b/Documentation/filesystems/dax.rst index 9a1b8fd9e82b..c04609d8ee24 100644 --- a/Documentation/filesystems/dax.rst +++ b/Documentation/filesystems/dax.rst @@ -23,11 +23,11 @@ on it as usual. The `DAX` code currently only supports files with a block size equal to your kernel's `PAGE_SIZE`, so you may need to specify a block size when creating the filesystem. -Currently 3 filesystems support `DAX`: ext2, ext4 and xfs. Enabling `DAX` on them -is different. +Currently 5 filesystems support `DAX`: ext2, ext4, xfs, virtiofs and erofs. +Enabling `DAX` on them is different. -Enabling DAX on ext2 --------------------- +Enabling DAX on ext2 and erofs +------------------------------ When mounting the filesystem, use the ``-o dax`` option on the command line or add 'dax' to the options in ``/etc/fstab``. This works to enable `DAX` on all files @@ -168,6 +168,22 @@ if the underlying media does not support dax and/or the filesystem is overridden with a mount option. +Enabling DAX on virtiofs +---------------------------- +The semantic of DAX on virtiofs is basically equal to that on ext4 and xfs, +except that when '-o dax=inode' is specified, virtiofs client derives the hint +whether DAX shall be enabled or not from virtiofs server through FUSE protocol, +rather than the persistent `FS_XFLAG_DAX` flag. That is, whether DAX shall be +enabled or not is completely determined by virtiofs server, while virtiofs +server itself may deploy various algorithm making this decision, e.g. depending +on the persistent `FS_XFLAG_DAX` flag on the host. + +It is still supported to set or clear persistent `FS_XFLAG_DAX` flag inside +guest, but it is not guaranteed that DAX will be enabled or disabled for +corresponding file then. Users inside guest still need to call statx(2) and +check the statx flag `STATX_ATTR_DAX` to see if DAX is enabled for this file. + + Implementation Tips for Block Driver Writers -------------------------------------------- |