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: 1f28476dcb98 ("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>
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index bb63e2b..1b79dd5 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -731,6 +731,8 @@
nfs_list_remove_request(req);
if (request_commit) {
kref_get(&req->wb_kref);
+ memcpy(&req->wb_verf, &hdr->verf.verifier,
+ sizeof(req->wb_verf));
nfs_mark_request_commit(req, hdr->lseg, &cinfo,
hdr->ds_commit_idx);
}
