FS-Cache: Add counters for entry/exit to/from cache operation functions

Count entries to and exits from cache operation table functions.  Maintain
these as a single counter that's added to or removed from as appropriate.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
index 724384e..6a3c48a 100644
--- a/fs/fscache/cache.c
+++ b/fs/fscache/cache.c
@@ -381,11 +381,15 @@
 
 	/* make sure all pages pinned by operations on behalf of the netfs are
 	 * written to disk */
+	fscache_stat(&fscache_n_cop_sync_cache);
 	cache->ops->sync_cache(cache);
+	fscache_stat_d(&fscache_n_cop_sync_cache);
 
 	/* dissociate all the netfs pages backed by this cache from the block
 	 * mappings in the cache */
+	fscache_stat(&fscache_n_cop_dissociate_pages);
 	cache->ops->dissociate_pages(cache);
+	fscache_stat_d(&fscache_n_cop_dissociate_pages);
 
 	/* we now have to destroy all the active objects pertaining to this
 	 * cache - which we do by passing them off to thread pool to be