NFS: Fix direct WRITE throughput regression
I measured a 50% throughput regression for large direct writes. The observed on-the-wire behavior is that the client sends every NFS WRITE twice: once as an UNSTABLE WRITE plus a COMMIT, and once as a FILE_SYNC WRITE. This is because the nfs_write_match_verf() check in nfs_direct_commit_complete() fails for every WRITE. Buffered writes use nfs_write_completion(), which sets req->wb_verf correctly. Direct writes use nfs_direct_write_completion(), which does not set req->wb_verf at all. This leaves req->wb_verf set to all zeroes for every direct WRITE, and thus nfs_direct_commit_completion() always sets NFS_ODIRECT_RESCHED_WRITES. This fix appears to restore nearly all of the lost performance. Fixes: 1f28476d ("NFS: Fix O_DIRECT commit verifier handling") Signed-off-by:Chuck Lever <chuck.lever@oracle.com> Signed-off-by:
Anna Schumaker <Anna.Schumaker@Netapp.com>
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