[PATCH 3/6] iocache: bump buffer mru priority every 50 accesses

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Darrick J. Wong <djwong@xxxxxxxxxx>

If a buffer is hot enough to survive more than 50 access without being
reclaimed, bump its priority to the next MRU so it sticks around longer.

Signed-off-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
---
 lib/support/cache.h   |    1 +
 lib/support/cache.c   |   16 ++++++++++++++++
 lib/support/iocache.c |    9 +++++++++
 3 files changed, 26 insertions(+)


diff --git a/lib/support/cache.h b/lib/support/cache.h
index f482948a3b6331..5a8e19f5d18e78 100644
--- a/lib/support/cache.h
+++ b/lib/support/cache.h
@@ -173,5 +173,6 @@ int cache_node_purge(struct cache *, cache_key_t, struct cache_node *);
 void cache_report(FILE *fp, const char *, struct cache *);
 int cache_overflowed(struct cache *);
 struct cache_node *cache_node_grab(struct cache *cache, struct cache_node *node);
+void cache_node_bump_priority(struct cache *cache, struct cache_node *node);
 
 #endif	/* __CACHE_H__ */
diff --git a/lib/support/cache.c b/lib/support/cache.c
index 7e1ddc3cc8788d..34df5cb51cd5e4 100644
--- a/lib/support/cache.c
+++ b/lib/support/cache.c
@@ -649,6 +649,22 @@ cache_node_put(
 		cache_shrink(cache);
 }
 
+/* Bump the priority of a cache node.  Caller must hold cn_mutex. */
+void
+cache_node_bump_priority(
+	struct cache		*cache,
+	struct cache_node	*node)
+{
+	int			*priop;
+
+	if (node->cn_priority == CACHE_DIRTY_PRIORITY)
+		priop = &node->cn_old_priority;
+	else
+		priop = &node->cn_priority;
+	if (*priop < CACHE_MAX_PRIORITY)
+		(*priop)++;
+}
+
 void
 cache_node_set_priority(
 	struct cache *		cache,
diff --git a/lib/support/iocache.c b/lib/support/iocache.c
index ab879e85d18f2a..92d88331bfa54d 100644
--- a/lib/support/iocache.c
+++ b/lib/support/iocache.c
@@ -56,6 +56,7 @@ struct iocache_buf {
 	blk64_t			block;
 	void			*buf;
 	errcode_t		write_error;
+	uint8_t			access;
 	unsigned int		uptodate:1;
 	unsigned int		dirty:1;
 };
@@ -552,6 +553,10 @@ static errcode_t iocache_read_blk64(io_channel channel,
 		}
 		if (ubuf->uptodate)
 			memcpy(buf, ubuf->buf, channel->block_size);
+		if (++ubuf->access > 50) {
+			cache_node_bump_priority(&data->cache, node);
+			ubuf->access = 0;
+		}
 		iocache_buf_unlock(ubuf);
 		cache_node_put(&data->cache, node);
 		if (retval)
@@ -613,6 +618,10 @@ static errcode_t iocache_write_blk64(io_channel channel,
 				     ubuf->uptodate ? CACHE_HIT : CACHE_MISS);
 		ubuf->dirty = 1;
 		ubuf->uptodate = 1;
+		if (++ubuf->access > 50) {
+			cache_node_bump_priority(&data->cache, node);
+			ubuf->access = 0;
+		}
 		iocache_buf_unlock(ubuf);
 		cache_node_put(&data->cache, node);
 	}