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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: 1f28476dcb
("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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@ -731,6 +731,8 @@ static void nfs_direct_write_completion(struct nfs_pgio_header *hdr)
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nfs_list_remove_request(req);
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if (request_commit) {
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kref_get(&req->wb_kref);
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memcpy(&req->wb_verf, &hdr->verf.verifier,
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sizeof(req->wb_verf));
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nfs_mark_request_commit(req, hdr->lseg, &cinfo,
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hdr->ds_commit_idx);
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}
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