3 files changed, 55 insertions, 2 deletions

diff --git a/usr/src/uts/common/fs/zfs/arc.c b/usr/src/uts/common/fs/zfs/arc.c
index f103274f29..7e1d42c3cf 100644
--- a/usr/src/uts/common/fs/zfs/arc.c
+++ b/usr/src/uts/common/fs/zfs/arc.c
@@ -468,8 +468,13 @@ typedef struct arc_stats {
 	 */
 	kstat_named_t arcstat_mutex_miss;
 	/*
+	 * Number of buffers skipped when updating the access state due to the
+	 * header having already been released after acquiring the hash lock.
+	 */
+	kstat_named_t arcstat_access_skip;
+	/*
 	 * Number of buffers skipped because they have I/O in progress, are
-	 * indrect prefetch buffers that have not lived long enough, or are
+	 * indirect prefetch buffers that have not lived long enough, or are
 	 * not from the spa we're trying to evict from.
 	 */
 	kstat_named_t arcstat_evict_skip;
@@ -711,6 +716,7 @@ static arc_stats_t arc_stats = {
 	{ "mfu_ghost_hits",		KSTAT_DATA_UINT64 },
 	{ "deleted",			KSTAT_DATA_UINT64 },
 	{ "mutex_miss",			KSTAT_DATA_UINT64 },
+	{ "access_skip",		KSTAT_DATA_UINT64 },
 	{ "evict_skip",			KSTAT_DATA_UINT64 },
 	{ "evict_not_enough",		KSTAT_DATA_UINT64 },
 	{ "evict_l2_cached",		KSTAT_DATA_UINT64 },
@@ -4714,6 +4720,50 @@ arc_access(arc_buf_hdr_t *hdr, kmutex_t *hash_lock)
 	}
 }
 
+/*
+ * This routine is called by dbuf_hold() to update the arc_access() state
+ * which otherwise would be skipped for entries in the dbuf cache.
+ */
+void
+arc_buf_access(arc_buf_t *buf)
+{
+	mutex_enter(&buf->b_evict_lock);
+	arc_buf_hdr_t *hdr = buf->b_hdr;
+
+	/*
+	 * Avoid taking the hash_lock when possible as an optimization.
+	 * The header must be checked again under the hash_lock in order
+	 * to handle the case where it is concurrently being released.
+	 */
+	if (hdr->b_l1hdr.b_state == arc_anon || HDR_EMPTY(hdr)) {
+		mutex_exit(&buf->b_evict_lock);
+		return;
+	}
+
+	kmutex_t *hash_lock = HDR_LOCK(hdr);
+	mutex_enter(hash_lock);
+
+	if (hdr->b_l1hdr.b_state == arc_anon || HDR_EMPTY(hdr)) {
+		mutex_exit(hash_lock);
+		mutex_exit(&buf->b_evict_lock);
+		ARCSTAT_BUMP(arcstat_access_skip);
+		return;
+	}
+
+	mutex_exit(&buf->b_evict_lock);
+
+	ASSERT(hdr->b_l1hdr.b_state == arc_mru ||
+	    hdr->b_l1hdr.b_state == arc_mfu);
+
+	DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr);
+	arc_access(hdr, hash_lock);
+	mutex_exit(hash_lock);
+
+	ARCSTAT_BUMP(arcstat_hits);
+	ARCSTAT_CONDSTAT(!HDR_PREFETCH(hdr),
+	    demand, prefetch, !HDR_ISTYPE_METADATA(hdr), data, metadata, hits);
+}
+
 /* a generic arc_done_func_t which you can use */
 /* ARGSUSED */
 void
diff --git a/usr/src/uts/common/fs/zfs/dbuf.c b/usr/src/uts/common/fs/zfs/dbuf.c
index 6d4d0a3332..aa46c90568 100644
--- a/usr/src/uts/common/fs/zfs/dbuf.c
+++ b/usr/src/uts/common/fs/zfs/dbuf.c
@@ -2652,8 +2652,10 @@ top:
 		return (SET_ERROR(ENOENT));
 	}
 
-	if (db->db_buf != NULL)
+	if (db->db_buf != NULL) {
+		arc_buf_access(db->db_buf);
 		ASSERT3P(db->db.db_data, ==, db->db_buf->b_data);
+	}
 
 	ASSERT(db->db_buf == NULL || arc_referenced(db->db_buf));
 
diff --git a/usr/src/uts/common/fs/zfs/sys/arc.h b/usr/src/uts/common/fs/zfs/sys/arc.h
index 641ae93e9c..87d2d1d329 100644
--- a/usr/src/uts/common/fs/zfs/sys/arc.h
+++ b/usr/src/uts/common/fs/zfs/sys/arc.h
@@ -170,6 +170,7 @@ void arc_loan_inuse_buf(arc_buf_t *buf, void *tag);
 void arc_buf_destroy(arc_buf_t *buf, void *tag);
 int arc_buf_size(arc_buf_t *buf);
 int arc_buf_lsize(arc_buf_t *buf);
+void arc_buf_access(arc_buf_t *buf);
 void arc_release(arc_buf_t *buf, void *tag);
 int arc_released(arc_buf_t *buf);
 void arc_buf_freeze(arc_buf_t *buf);