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Subject: [PATCH RFC 08/30] NFSD: Report the number of items evicted by the LRU
 walk
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org, netdev@vger.kernel.org
Cc:     david@fromorbit.com, tgraf@suug.ch, jlayton@redhat.com
Date:   Wed, 22 Jun 2022 10:13:38 -0400
Message-ID: <165590721886.75778.3954208768212592776.stgit@manet.1015granger.net>
In-Reply-To: <165590626293.75778.9843437418112335153.stgit@manet.1015granger.net>
References: <165590626293.75778.9843437418112335153.stgit@manet.1015granger.net>
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Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/filecache.c |   14 +++++++++++---
 fs/nfsd/trace.h     |   29 +++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index b1e7588d578a..d597acfdab28 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -45,6 +45,7 @@ struct nfsd_fcache_bucket {
 static DEFINE_PER_CPU(unsigned long, nfsd_file_cache_hits);
 static DEFINE_PER_CPU(unsigned long, nfsd_file_acquisitions);
 static DEFINE_PER_CPU(unsigned long, nfsd_file_releases);
+static DEFINE_PER_CPU(unsigned long, nfsd_file_evictions);
 
 struct nfsd_fcache_disposal {
 	struct work_struct work;
@@ -482,9 +483,12 @@ static void
 nfsd_file_gc(void)
 {
 	LIST_HEAD(dispose);
+	unsigned long ret;
 
-	list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb,
-		      &dispose, LONG_MAX);
+	ret = list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb,
+			    &dispose, LONG_MAX);
+	this_cpu_add(nfsd_file_evictions, ret);
+	trace_nfsd_file_gc_evicted(ret, list_lru_count(&nfsd_file_lru));
 	nfsd_file_gc_dispose_list(&dispose);
 }
 
@@ -509,6 +513,8 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc)
 
 	ret = list_lru_shrink_walk(&nfsd_file_lru, sc,
 				   nfsd_file_lru_cb, &dispose);
+	this_cpu_add(nfsd_file_evictions, ret);
+	trace_nfsd_file_shrinker_evicted(ret, list_lru_count(&nfsd_file_lru));
 	nfsd_file_gc_dispose_list(&dispose);
 	return ret;
 }
@@ -1085,7 +1091,7 @@ nfsd_file_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
  */
 static int nfsd_file_cache_stats_show(struct seq_file *m, void *v)
 {
-	unsigned long hits = 0, acquisitions = 0, releases = 0;
+	unsigned long hits = 0, acquisitions = 0, releases = 0, evictions = 0;
 	unsigned int i, count = 0, longest = 0;
 
 	/*
@@ -1106,6 +1112,7 @@ static int nfsd_file_cache_stats_show(struct seq_file *m, void *v)
 		hits += per_cpu(nfsd_file_cache_hits, i);
 		acquisitions += per_cpu(nfsd_file_acquisitions, i);
 		releases += per_cpu(nfsd_file_releases, i);
+		evictions += per_cpu(nfsd_file_evictions, i);
 	}
 
 	seq_printf(m, "total entries: %u\n", count);
@@ -1114,6 +1121,7 @@ static int nfsd_file_cache_stats_show(struct seq_file *m, void *v)
 	seq_printf(m, "cache hits:    %lu\n", hits);
 	seq_printf(m, "acquisitions:  %lu\n", acquisitions);
 	seq_printf(m, "releases:      %lu\n", releases);
+	seq_printf(m, "evictions:     %lu\n", evictions);
 	if (releases)
 		seq_printf(m, "mean age (ms): %ld\n",
 			atomic_long_read(&nfsd_file_total_age) / releases);
diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index a60ead3b227a..c055c6361bd5 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -851,6 +851,35 @@ TRACE_EVENT(nfsd_file_fsnotify_handle_event,
 			__entry->nlink, __entry->mode, __entry->mask)
 );
 
+DECLARE_EVENT_CLASS(nfsd_file_lruwalk_class,
+	TP_PROTO(
+		unsigned long evicted,
+		unsigned long remaining
+	),
+	TP_ARGS(evicted, remaining),
+	TP_STRUCT__entry(
+		__field(unsigned long, evicted)
+		__field(unsigned long, remaining)
+	),
+	TP_fast_assign(
+		__entry->evicted = evicted;
+		__entry->remaining = remaining;
+	),
+	TP_printk("%lu entries evicted, %lu remaining",
+		__entry->evicted, __entry->remaining)
+);
+
+#define DEFINE_NFSD_FILE_LRUWALK_EVENT(name)				\
+DEFINE_EVENT(nfsd_file_lruwalk_class, name,				\
+	TP_PROTO(							\
+		unsigned long evicted,					\
+		unsigned long remaining					\
+	),								\
+	TP_ARGS(evicted, remaining))
+
+DEFINE_NFSD_FILE_LRUWALK_EVENT(nfsd_file_gc_evicted);
+DEFINE_NFSD_FILE_LRUWALK_EVENT(nfsd_file_shrinker_evicted);
+
 #include "cache.h"
 
 TRACE_DEFINE_ENUM(RC_DROPIT);