ext4: make online defragmentation support large folios

move_extent_per_page() currently assumes that each folio is the size of
PAGE_SIZE and only copies data for one page. ext4_move_extents() should
call move_extent_per_page() for each page. To support larger folios,
simply modify the calculations for the block start and end offsets
within the folio based on the provided range of 'data_offset_in_page'
and 'block_len_in_page'. This function will continue to handle PAGE_SIZE
of data at a time and will not convert this function to manage an entire
folio. Additionally, we use the source folio to copy data, so it doesn't
matter if the source and dest folios are different in size.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250512063319.3539411-8-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: zhangyi089

fs/ext4/move_extent.c

@@ -269,7 +269,7 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 	unsigned int tmp_data_size, data_size, replaced_size;
 	int i, err2, jblocks, retries = 0;
 	int replaced_count = 0;
-	int from = data_offset_in_page << orig_inode->i_blkbits;
+	int from;
 	int blocks_per_page = PAGE_SIZE >> orig_inode->i_blkbits;
 	struct super_block *sb = orig_inode->i_sb;
 	struct buffer_head *bh = NULL;
@@ -323,11 +323,6 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 	 * hold page's lock, if it is still the case data copy is not
 	 * necessary, just swap data blocks between orig and donor.
 	 */
-
-	VM_BUG_ON_FOLIO(folio_test_large(folio[0]), folio[0]);
-	VM_BUG_ON_FOLIO(folio_test_large(folio[1]), folio[1]);
-	VM_BUG_ON_FOLIO(folio_nr_pages(folio[0]) != folio_nr_pages(folio[1]), folio[1]);
-
 	if (unwritten) {
 		ext4_double_down_write_data_sem(orig_inode, donor_inode);
 		/* If any of extents in range became initialized we have to
@@ -360,6 +355,8 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 		goto unlock_folios;
 	}
 data_copy:
+	from = offset_in_folio(folio[0],
+			       orig_blk_offset << orig_inode->i_blkbits);
 	*err = mext_page_mkuptodate(folio[0], from, from + replaced_size);
 	if (*err)
 		goto unlock_folios;
@@ -390,7 +387,7 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 	if (!bh)
 		bh = create_empty_buffers(folio[0],
 				1 << orig_inode->i_blkbits, 0);
-	for (i = 0; i < data_offset_in_page; i++)
+	for (i = 0; i < from >> orig_inode->i_blkbits; i++)
 		bh = bh->b_this_page;
 	for (i = 0; i < block_len_in_page; i++) {
 		*err = ext4_get_block(orig_inode, orig_blk_offset + i, bh, 0);