btrfs: rename some variables at try_release_extent_mapping()

Rename the following variables:

1) "btrfs_inode" to "inode", because it's shorter to type and clear, and
   we don't have a VFS inode here as well, so there's no confusion;

2) "tree" to "io_tree", to be clear which tree we are dealing with, since
   we use 2 different trees in the function;

3) "map" to "extent_tree" since "map" gives the idea we are dealing with
   an extent map for example, but we are dealing with the inode's extent
   tree (the tree which stores extent maps).

These also make the next patches simpler.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -2398,9 +2398,9 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 	struct extent_map *em;
 	u64 start = page_offset(page);
 	u64 end = start + PAGE_SIZE - 1;
-	struct btrfs_inode *btrfs_inode = page_to_inode(page);
-	struct extent_io_tree *tree = &btrfs_inode->io_tree;
-	struct extent_map_tree *map = &btrfs_inode->extent_tree;
+	struct btrfs_inode *inode = page_to_inode(page);
+	struct extent_io_tree *io_tree = &inode->io_tree;
+	struct extent_map_tree *extent_tree = &inode->extent_tree;
 
 	if (gfpflags_allow_blocking(mask) &&
 	    page->mapping->host->i_size > SZ_16M) {
@@ -2410,19 +2410,19 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 			u64 cur_gen;
 
 			len = end - start + 1;
-			write_lock(&map->lock);
-			em = lookup_extent_mapping(map, start, len);
+			write_lock(&extent_tree->lock);
+			em = lookup_extent_mapping(extent_tree, start, len);
 			if (!em) {
-				write_unlock(&map->lock);
+				write_unlock(&extent_tree->lock);
 				break;
 			}
 			if ((em->flags & EXTENT_FLAG_PINNED) ||
 			    em->start != start) {
-				write_unlock(&map->lock);
+				write_unlock(&extent_tree->lock);
 				free_extent_map(em);
 				break;
 			}
-			if (test_range_bit_exists(tree, em->start,
+			if (test_range_bit_exists(io_tree, em->start,
 						  extent_map_end(em) - 1,
 						  EXTENT_LOCKED))
 				goto next;
@@ -2442,7 +2442,7 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 			 * Otherwise don't remove it, we could be racing with an
 			 * ongoing fast fsync that could miss the new extent.
 			 */
-			fs_info = btrfs_inode->root->fs_info;
+			fs_info = inode->root->fs_info;
 			spin_lock(&fs_info->trans_lock);
 			cur_gen = fs_info->generation;
 			spin_unlock(&fs_info->trans_lock);
@@ -2457,12 +2457,12 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 			 * hurts the fsync performance for workloads with a data
 			 * size that exceeds or is close to the system's memory).
 			 */
-			remove_extent_mapping(btrfs_inode, em);
+			remove_extent_mapping(inode, em);
 			/* once for the rb tree */
 			free_extent_map(em);
 next:
 			start = extent_map_end(em);
-			write_unlock(&map->lock);
+			write_unlock(&extent_tree->lock);
 
 			/* once for us */
 			free_extent_map(em);
@@ -2470,7 +2470,7 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 			cond_resched(); /* Allow large-extent preemption. */
 		}
 	}
-	return try_release_extent_state(tree, page, mask);
+	return try_release_extent_state(io_tree, page, mask);
 }
 
 struct btrfs_fiemap_entry {