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| author | Jeffle Xu <jefflexu@linux.alibaba.com> | 2021-11-25 10:05:30 +0300 |
|---|---|---|
| committer | Miklos Szeredi <mszeredi@redhat.com> | 2021-12-14 13:09:37 +0300 |
| commit | 073c3ab6ae0123601b5378e8f49c7b8ec4625f32 (patch) | |
| tree | 9f6aa49c700e7ee5fd502f04abe05f6e770be96a /Documentation/filesystems/dax.rst | |
| parent | c3cb6f935e322fa183988032e318b293d9e4fe53 (diff) | |
| download | linux-073c3ab6ae0123601b5378e8f49c7b8ec4625f32.tar.xz | |
Documentation/filesystem/dax: DAX on virtiofs
Record DAX on virtiofs and the semantic difference with that on ext4
and xfs.
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'Documentation/filesystems/dax.rst')
| -rw-r--r-- | Documentation/filesystems/dax.rst | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/Documentation/filesystems/dax.rst b/Documentation/filesystems/dax.rst index 9a1b8fd9e82b..e3b30429d703 100644 --- a/Documentation/filesystems/dax.rst +++ b/Documentation/filesystems/dax.rst @@ -23,8 +23,8 @@ 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 4 filesystems support `DAX`: ext2, ext4, xfs and virtiofs. +Enabling `DAX` on them is different. Enabling DAX on ext2 -------------------- @@ -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 -------------------------------------------- |