diff options
| author | Mike Snitzer <snitzer@kernel.org> | 2024-11-15 20:40:53 -0500 |
|---|---|---|
| committer | Anna Schumaker <anna.schumaker@oracle.com> | 2025-01-14 17:04:02 -0500 |
| commit | 3feec68563dda59517f83d19123aa287a1dfd068 (patch) | |
| tree | 00b3bddf355513cded25b02e3601d895b0243e6f /Documentation/filesystems | |
| parent | 49fd4e34751e90e6df009b70cd0659dc839e7ca8 (diff) | |
nfs/localio: add direct IO enablement with sync and async IO support
This commit simply adds the required O_DIRECT plumbing. It doesn't
address the fact that NFS doesn't ensure all writes are page aligned
(nor device logical block size aligned as required by O_DIRECT).
Because NFS will read-modify-write for IO that isn't aligned, LOCALIO
will not use O_DIRECT semantics by default if/when an application
requests the use of O_DIRECT. Allow the use of O_DIRECT semantics by:
1: Adding a flag to the nfs_pgio_header struct to allow the NFS
O_DIRECT layer to signal that O_DIRECT was used by the application
2: Adding a 'localio_O_DIRECT_semantics' NFS module parameter that
when enabled will cause LOCALIO to use O_DIRECT semantics (this may
cause IO to fail if applications do not properly align their IO).
This commit is derived from code developed by Weston Andros Adamson.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/nfs/localio.rst | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/filesystems/nfs/localio.rst b/Documentation/filesystems/nfs/localio.rst index bd1967e2eab3..20fc901a08f4 100644 --- a/Documentation/filesystems/nfs/localio.rst +++ b/Documentation/filesystems/nfs/localio.rst @@ -306,6 +306,19 @@ is issuing IO to the underlying local filesystem that it is sharing with the NFS server. See: fs/nfs/localio.c:nfs_local_doio() and fs/nfs/localio.c:nfs_local_commit(). +With normal NFS that makes use of RPC to issue IO to the server, if an +application uses O_DIRECT the NFS client will bypass the pagecache but +the NFS server will not. Because the NFS server's use of buffered IO +affords applications to be less precise with their alignment when +issuing IO to the NFS client. LOCALIO can be configured to use O_DIRECT +semantics by setting the 'localio_O_DIRECT_semantics' nfs module +parameter to Y, e.g.: + + echo Y > /sys/module/nfs/parameters/localio_O_DIRECT_semantics + +Once enabled, it will cause LOCALIO to use O_DIRECT semantics (this may +cause IO to fail if applications do not properly align their IO). + Security ======== |