[PATCH 7/7] NFSD: Record DRC population in lookup tracepoints

[Chuck Lever <cel@kernel.org>]

nfsd_drc_found reports the outcome of a lookup but not how full the
cache was at the time, so a trace cannot show whether a miss happened
under pressure.

Add an entries= field. The count is passed as an explicit argument
rather than read from nn->num_drc_entries in TP_fast_assign, so that
per-connection lookup paths can later supply their own depth without
changing the tracepoint format.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfscache.c |  3 ++-
 fs/nfsd/trace.h    | 11 +++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index dfbcc75fbb12..b917af667a89 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -606,7 +606,8 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
 	}
 
 out_trace:
-	trace_nfsd_drc_found(nn, rqstp, rtn);
+	trace_nfsd_drc_found(nn, atomic_read(&nn->num_drc_entries),
+			     rqstp, rtn);
 out_unlock:
 	spin_unlock(&b->cache_lock);
 out:
diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index f1d399b3e51c..75b1d828f2e0 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -1500,23 +1500,26 @@ TRACE_DEFINE_ENUM(RC_DOIT);
 TRACE_EVENT(nfsd_drc_found,
 	TP_PROTO(
 		const struct nfsd_net *nn,
+		unsigned int num_drc_entries,
 		const struct svc_rqst *rqstp,
 		int result
 	),
-	TP_ARGS(nn, rqstp, result),
+	TP_ARGS(nn, num_drc_entries, rqstp, result),
 	TP_STRUCT__entry(
 		__field(unsigned long long, boot_time)
+		__field(unsigned int, num_drc_entries)
 		__field(unsigned long, result)
 		__field(u32, xid)
 	),
 	TP_fast_assign(
 		__entry->boot_time = nn->boot_time;
+		__entry->num_drc_entries = num_drc_entries;
 		__entry->result = result;
 		__entry->xid = be32_to_cpu(rqstp->rq_xid);
 	),
-	TP_printk("boot_time=%16llx xid=0x%08x result=%s",
-		__entry->boot_time, __entry->xid,
-		show_drc_retval(__entry->result))
+	TP_printk("boot_time=%16llx entries=%u xid=0x%08x result=%s",
+		__entry->boot_time, __entry->num_drc_entries,
+		__entry->xid, show_drc_retval(__entry->result))
 
 );
 

-- 
2.55.0