btrfs: remove i_size restriction at try_release_extent_mapping()

Currently we don't attempt to release extent maps if the inode has an
i_size that is not greater than 16M. This condition was added way back
in 2008 by commit 70dec807 ("Btrfs: extent_io and extent_state
optimizations"), without any explanation about it. A quick chat with
Chris on slack revealed that the goal was probably to release the extent
maps for small files only when closing the inode. This however can be
harmful in case we have tons of such files being kept open for very long
periods of time, since we will consume more and more pages for extent
maps.

So remove the condition.
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

@@ -2402,8 +2402,7 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 	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) {
+	if (gfpflags_allow_blocking(mask)) {
 		u64 len;
 		while (start <= end) {
 			const u64 cur_gen = btrfs_get_fs_generation(inode->root->fs_info);