When NFSD_IO_DIRECT is selected via the
/sys/kernel/debug/nfsd/io_cache_write experimental tunable, split
incoming unaligned NFS WRITE requests into a prefix, middle and
suffix segment, as needed. The middle segment is now DIO-aligned and
the prefix and/or suffix are unaligned. Synchronous buffered IO is
used for the unaligned segments, and IOCB_DIRECT is used for the
middle DIO-aligned extent.
Although IOCB_DIRECT avoids the use of the page cache, by itself it
doesn't guarantee data durability. For UNSTABLE WRITE requests,
durability is obtained by a subsequent NFS COMMIT request.
Signed-off-by: Mike Snitzer <snitzer@kernel.org> Co-developed-by: Chuck Lever <chuck.lever@oracle.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
gentwo / linux / .git / commit