dm thin metadata: introduce THIN_MAX_CONCURRENT_LOCKS

Introduce THIN_MAX_CONCURRENT_LOCKS into dm-thin-metadata to
give a name to an otherwise "magic" number.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin-metadata.c

@@ -80,6 +80,12 @@
 #define THIN_METADATA_CACHE_SIZE 64
 #define SECTOR_TO_BLOCK_SHIFT 3
 
+/*
+ *  3 for btree insert +
+ *  2 for btree lookup used within space map
+ */
+#define THIN_MAX_CONCURRENT_LOCKS 5
+
 /* This should be plenty */
 #define SPACE_MAP_ROOT_SIZE 128
 
@@ -668,13 +674,9 @@ struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
 		return ERR_PTR(-ENOMEM);
 	}
 
-	/*
-	 * Max hex locks:
-	 *  3 for btree insert +
-	 *  2 for btree lookup used within space map
-	 */
 	bm = dm_block_manager_create(bdev, THIN_METADATA_BLOCK_SIZE,
-				     THIN_METADATA_CACHE_SIZE, 5);
+				     THIN_METADATA_CACHE_SIZE,
+				     THIN_MAX_CONCURRENT_LOCKS);
 	if (!bm) {
 		DMERR("could not create block manager");
 		kfree(pmd);