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Diffstat (limited to 'Documentation/filesystems/nfs')
| -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 ======== |