[PATCH v2 6/7] NFSD: Add tracepoints for DRC entry eviction

[Chuck Lever <cel@kernel.org>]

The DRC pruning path evicts entries for memory pressure, expiry, and
implied ACK, and none of these emit a trace event. There is no way to
confirm that implied-ACK eviction fires or to compare its rate with
the other paths.

Add a tracepoint for each eviction reason.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfscache.c | 12 +++++++++---
 fs/nfsd/trace.h    | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 7a09a79a2d6e..dfbcc75fbb12 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -304,13 +304,19 @@ nfsd_prune_bucket_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
 
 	/* The bucket LRU is ordered oldest-first. */
 	list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
-		if (atomic_read(&nn->num_drc_entries) > nn->max_drc_entries)
+		if (atomic_read(&nn->num_drc_entries) > nn->max_drc_entries) {
+			trace_nfsd_drc_evict_pressure(nn, rp);
 			goto evict;
-		if (time_before_eq(rp->c_timestamp, expiry))
+		}
+		if (time_before_eq(rp->c_timestamp, expiry)) {
+			trace_nfsd_drc_evict_expired(nn, rp);
 			goto evict;
+		}
 		if (rp->c_state == RC_DONE &&
-		    nfsd_cacherep_implied_ack(xprt, rp))
+		    nfsd_cacherep_implied_ack(xprt, rp)) {
+			trace_nfsd_drc_evict_implied_ack(nn, rp);
 			goto evict;
+		}
 		/*
 		 * Only implied ACK evicts out of age order, and only on an
 		 * ordered transport; otherwise the first non-evictable entry
diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index 7d7a1483109a..c8468f67abe0 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -1544,6 +1544,44 @@ TRACE_EVENT(nfsd_drc_mismatch,
 		__entry->ingress)
 );
 
+DECLARE_EVENT_CLASS(nfsd_drc_entry_class,
+	TP_PROTO(
+		const struct nfsd_net *nn,
+		const struct nfsd_cacherep *rp
+	),
+	TP_ARGS(nn, rp),
+	TP_STRUCT__entry(
+		__field(unsigned long long, boot_time)
+		__field(unsigned int, num_drc_entries)
+		__field(u32, xid)
+		__field(unsigned int, xprt)
+		__field(unsigned long, age)
+	),
+	TP_fast_assign(
+		__entry->boot_time = nn->boot_time;
+		__entry->num_drc_entries = atomic_read(&nn->num_drc_entries);
+		__entry->xid = be32_to_cpu(rp->c_key.k_xid);
+		__entry->xprt = rp->c_xprt;
+		__entry->age = time_is_after_jiffies(rp->c_timestamp) ?
+				1 : jiffies - rp->c_timestamp;
+	),
+	TP_printk("boot_time=%16llx entries=%u xid=0x%08x xprt=%u age=%lu",
+		__entry->boot_time, __entry->num_drc_entries,
+		__entry->xid, __entry->xprt, __entry->age)
+);
+
+#define DEFINE_NFSD_DRC_ENTRY_EVENT(name)			\
+DEFINE_EVENT(nfsd_drc_entry_class, nfsd_drc_##name,		\
+	TP_PROTO(						\
+		const struct nfsd_net *nn,			\
+		const struct nfsd_cacherep *rp			\
+	),							\
+	TP_ARGS(nn, rp))
+
+DEFINE_NFSD_DRC_ENTRY_EVENT(evict_pressure);
+DEFINE_NFSD_DRC_ENTRY_EVENT(evict_expired);
+DEFINE_NFSD_DRC_ENTRY_EVENT(evict_implied_ack);
+
 TRACE_EVENT(nfsd_cb_args,
 	TP_PROTO(
 		const struct nfs4_client *clp,

-- 
2.55.0