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Subject: [PATCH v1 4/6] NFSD: Refactor the duplicate reply cache shrinker
From:   Chuck Lever <cel@kernel.org>
To:     linux-nfs@vger.kernel.org
Cc:     Chuck Lever <chuck.lever@oracle.com>
Date:   Sun, 09 Jul 2023 11:45:35 -0400
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From: Chuck Lever <chuck.lever@oracle.com>

Avoid holding the bucket lock while freeing cache entries. This
change also caps the number of entries that are freed when the
shrinker calls to reduce the shrinker's impact on the cache's
effectiveness.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfscache.c |   82 +++++++++++++++++++++++++---------------------------
 1 file changed, 39 insertions(+), 43 deletions(-)

diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index c8b572d2c72a..c08078ac9284 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -309,68 +309,64 @@ nfsd_prune_bucket_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
 	}
 }
 
-static long prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn,
-			 unsigned int max)
+/**
+ * nfsd_reply_cache_count - count_objects method for the DRC shrinker
+ * @shrink: our registered shrinker context
+ * @sc: garbage collection parameters
+ *
+ * Returns the total number of entries in the duplicate reply cache. To
+ * keep things simple and quick, this is not the number of expired entries
+ * in the cache (ie, the number that would be removed by a call to
+ * nfsd_reply_cache_scan).
+ */
+static unsigned long
+nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
 {
-	struct svc_cacherep *rp, *tmp;
-	long freed = 0;
+	struct nfsd_net *nn = container_of(shrink,
+				struct nfsd_net, nfsd_reply_cache_shrinker);
 
-	list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
-		/*
-		 * Don't free entries attached to calls that are still
-		 * in-progress, but do keep scanning the list.
-		 */
-		if (rp->c_state == RC_INPROG)
-			continue;
-		if (atomic_read(&nn->num_drc_entries) <= nn->max_drc_entries &&
-		    time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
-			break;
-		nfsd_reply_cache_free_locked(b, rp, nn);
-		if (max && freed++ > max)
-			break;
-	}
-	return freed;
+	return atomic_read(&nn->num_drc_entries);
 }
 
-/*
- * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
- * Also prune the oldest ones when the total exceeds the max number of entries.
+/**
+ * nfsd_reply_cache_scan - scan_objects method for the DRC shrinker
+ * @shrink: our registered shrinker context
+ * @sc: garbage collection parameters
+ *
+ * Free expired entries on each bucket's LRU list until we've released
+ * nr_to_scan freed objects. Nothing will be released if the cache
+ * has not exceeded it's max_drc_entries limit.
+ *
+ * Returns the number of entries released by this call.
  */
-static long
-prune_cache_entries(struct nfsd_net *nn)
+static unsigned long
+nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
+	struct nfsd_net *nn = container_of(shrink,
+				struct nfsd_net, nfsd_reply_cache_shrinker);
+	unsigned long freed = 0;
+	LIST_HEAD(dispose);
 	unsigned int i;
-	long freed = 0;
 
 	for (i = 0; i < nn->drc_hashsize; i++) {
 		struct nfsd_drc_bucket *b = &nn->drc_hashtbl[i];
 
 		if (list_empty(&b->lru_head))
 			continue;
+
 		spin_lock(&b->cache_lock);
-		freed += prune_bucket(b, nn, 0);
+		nfsd_prune_bucket_locked(nn, b, 0, &dispose);
 		spin_unlock(&b->cache_lock);
-	}
-	return freed;
-}
 
-static unsigned long
-nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
-{
-	struct nfsd_net *nn = container_of(shrink,
-				struct nfsd_net, nfsd_reply_cache_shrinker);
+		freed += nfsd_cacherep_dispose(&dispose);
+		if (freed > sc->nr_to_scan)
+			break;
+	}
 
-	return atomic_read(&nn->num_drc_entries);
+	trace_nfsd_drc_gc(nn, freed);
+	return freed;
 }
 
-static unsigned long
-nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
-{
-	struct nfsd_net *nn = container_of(shrink,
-				struct nfsd_net, nfsd_reply_cache_shrinker);
-
-	return prune_cache_entries(nn);
-}
 /*
  * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
  */