btrfs: move larger data folios out of experimental features

This feature was introduced in v6.17 under experimental, and we had
several small bugs related to or exposed by that feature:

 e9e3b22 ("btrfs: fix beyond-EOF write handling")
 18de34d ("btrfs: truncate ordered extent when skipping writeback past i_size")

Otherwise, the feature has been frequently tested by btrfs developers.

The latest fix only arrived in v6.19. After three releases, I think it's time
to move this feature out of experimental.

And since we're here, also remove the comment about the bitmap size
limit, which is no longer relevant in the context, and will soon be
outdated for the incoming huge folio support.

Reviewed-by: Neal Gompa <neal@gompa.dev>
Signed-off-by: Qu Wenruo <wqu@suse.com>

Author: adam900710

fs/btrfs/Kconfig

@@ -106,7 +106,7 @@ config BTRFS_EXPERIMENTAL
 
 	  - extent tree v2 - complex rework of extent tracking
 
-	  - large folio and block size (> page size) support
+	  - block size (> page size) support
 
 	  - asynchronous checksum generation for data writes
 

fs/btrfs/btrfs_inode.h

@@ -500,12 +500,9 @@ static inline void btrfs_set_inode_mapping_order(struct btrfs_inode *inode)
 	/* Metadata inode should not reach here. */
 	ASSERT(is_data_inode(inode));
 
-	/* We only allow BITS_PER_LONGS blocks for each bitmap. */
-#ifdef CONFIG_BTRFS_EXPERIMENTAL
 	mapping_set_folio_order_range(inode->vfs_inode.i_mapping,
 				      inode->root->fs_info->block_min_order,
 				      inode->root->fs_info->block_max_order);
-#endif
 }
 
 void btrfs_calculate_block_csum_folio(struct btrfs_fs_info *fs_info,

fs/btrfs/defrag.c

@@ -859,23 +859,6 @@ static struct folio *defrag_prepare_one_folio(struct btrfs_inode *inode, pgoff_t
 	if (IS_ERR(folio))
 		return folio;
 
-	/*
-	 * Since we can defragment files opened read-only, we can encounter
-	 * transparent huge pages here (see CONFIG_READ_ONLY_THP_FOR_FS).
-	 *
-	 * The IO for such large folios is not fully tested, thus return
-	 * an error to reject such folios unless it's an experimental build.
-	 *
-	 * Filesystem transparent huge pages are typically only used for
-	 * executables that explicitly enable them, so this isn't very
-	 * restrictive.
-	 */
-	if (!IS_ENABLED(CONFIG_BTRFS_EXPERIMENTAL) && folio_test_large(folio)) {
-		folio_unlock(folio);
-		folio_put(folio);
-		return ERR_PTR(-ETXTBSY);
-	}
-
 	ret = set_folio_extent_mapped(folio);
 	if (ret < 0) {
 		folio_unlock(folio);