[PATCH 07/11] NFSv4/flexfiles: derive ffil_ops_requested rather than storing it

[Mike Snitzer <snitzer@kernel.org>]

From: Mike Snitzer <snitzer@hammerspace.com>

nfs4_ff_io_stat::ops_requested carries no information that the stripe
does not already hold.  An op is in flight from the moment it is counted
as requested until it is counted as completed, and the previous patch
put both halves of that accounting in one place each, so

	ops_requested == ops_completed + ops_in_flight

holds at all times under the lock.

Drop the field and compute the value at encode time.  It had exactly one
producer and one consumer, the LAYOUTSTATS encoder, so nothing else
needs to change and the wire format is untouched -- ffil_ops_requested
is still a uint64, and nfs4_ff_ops_requested() returns __u64.
ff_layout_encode_io_latency() now takes the whole nfs4_ff_layoutstat,
since the in-flight count lives beside the statistics rather than in
them.

This takes 8 bytes off each direction's statistics, which is what lets
each direction fit in a cacheline of its own; see the next patch.

Signed-off-by: Mike Snitzer <snitzer@hammerspace.com>
---
 fs/nfs/flexfilelayout/flexfilelayout.c | 12 +++++-------
 fs/nfs/flexfilelayout/flexfilelayout.h | 19 ++++++++++++++++++-
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index bfe8288a14a08..846544977cf30 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -764,7 +764,6 @@ nfs4_ff_layoutstat_start_io(struct nfs4_ff_layout_ds_stripe *dss_info,
 	lockdep_assert_held(&dss_info->lock);
 
 	nfs4_ff_start_busy_timer(&layoutstat->busy_timer, now);
-	layoutstat->io_stat.ops_requested++;
 	layoutstat->io_stat.bytes_requested += requested;
 
 	nfs4_ff_layoutstat_set_start_time(dss_info, now);
@@ -3066,12 +3065,13 @@ ff_layout_encode_nfstime(struct xdr_stream *xdr,
 
 static void
 ff_layout_encode_io_latency(struct xdr_stream *xdr,
-			    struct nfs4_ff_io_stat *stat)
+			    const struct nfs4_ff_layoutstat *layoutstat)
 {
+	const struct nfs4_ff_io_stat *stat = &layoutstat->io_stat;
 	__be32 *p;
 
 	p = xdr_reserve_space(xdr, 5 * 8);
-	p = xdr_encode_hyper(p, stat->ops_requested);
+	p = xdr_encode_hyper(p, nfs4_ff_ops_requested(layoutstat));
 	p = xdr_encode_hyper(p, stat->bytes_requested);
 	p = xdr_encode_hyper(p, stat->ops_completed);
 	p = xdr_encode_hyper(p, stat->bytes_completed);
@@ -3101,11 +3101,9 @@ ff_layout_encode_ff_layoutupdate(struct xdr_stream *xdr,
 	xdr_encode_opaque(p, fh->data, fh->size);
 	/* ff_io_latency4 read */
 	spin_lock(&dss_info->lock);
-	ff_layout_encode_io_latency(xdr,
-				    &dss_info->read_stat.io_stat);
+	ff_layout_encode_io_latency(xdr, &dss_info->read_stat);
 	/* ff_io_latency4 write */
-	ff_layout_encode_io_latency(xdr,
-				    &dss_info->write_stat.io_stat);
+	ff_layout_encode_io_latency(xdr, &dss_info->write_stat);
 	spin_unlock(&dss_info->lock);
 	/* nfstime4 */
 	ff_layout_encode_nfstime(xdr,
diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index b0653a652d3b8..23f665fef4985 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -55,7 +55,6 @@ struct nfs4_ff_layout_ds_err {
 };
 
 struct nfs4_ff_io_stat {
-	__u64				ops_requested;
 	__u64				bytes_requested;
 	__u64				ops_completed;
 	__u64				bytes_completed;
@@ -78,6 +77,24 @@ struct nfs4_ff_layoutstat {
 	struct nfs4_ff_busy_timer busy_timer;
 };
 
+/*
+ * ffil_ops_requested is not stored.  An op is in flight from the moment it is
+ * counted as requested until it is counted as completed, so
+ *
+ *	ops_requested == ops_completed + ops_in_flight
+ *
+ * holds by construction; see nfs4_ff_layoutstat_start_io() and
+ * nfs4_ff_layoutstat_end_io(), which maintain both halves together.
+ *
+ * Caller must hold the lock guarding this nfs4_ff_layoutstat.
+ */
+static inline __u64
+nfs4_ff_ops_requested(const struct nfs4_ff_layoutstat *layoutstat)
+{
+	return layoutstat->io_stat.ops_completed +
+	       layoutstat->busy_timer.ops_in_flight;
+}
+
 struct nfs4_ff_layout_mirror;
 
 struct nfs4_ff_layout_ds_stripe {
-- 
2.52.0