ext4: don't copy non-existent gdt blocks when resizing

The resize code was copying blocks at the beginning of each block
group in order to copy the superblock and block group descriptor table
(gdt) blocks.  This was, unfortunately, being done even for block
groups that did not have super blocks or gdt blocks.  This is a
complete waste of perfectly good I/O bandwidth, to skip writing those
blocks for sparse bg's.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 591f4bda1146d5335b5bb1ffff4ef5a5b645c8ee..a0ee26c23dd83375ac74928df688da6903e57c47 100644 (file)
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -456,6 +456,9 @@ static int setup_new_flex_group_blocks(struct super_block *sb,
                gdblocks = ext4_bg_num_gdb(sb, group);
                start = ext4_group_first_block_no(sb, group);
 
+               if (!ext4_bg_has_super(sb, group))
+                       goto handle_itb;
+
                /* Copy all of the GDT blocks into the backup in this group */
                for (j = 0, block = start + 1; j < gdblocks; j++, block++) {
                        struct buffer_head *gdb;
@@ -498,6 +501,7 @@ static int setup_new_flex_group_blocks(struct super_block *sb,
                                goto out;
                }
 
+handle_itb:
                /* Initialize group tables of the grop @group */
                if (!(bg_flags[i] & EXT4_BG_INODE_ZEROED))
                        goto handle_bb;