ext4: don't call update_backups() multiple times for the same bg

When performing an online resize, we add a bunch of groups at one time
in ext4_flex_group_add, so in most cases a lot of group descriptors
will be in the same group block. But in the end of this function,
update_backups will be called for every group descriptor and the same
block will be copied and journalled again and again.  It is really a
waste.

Fix things so we only update a particular bg descriptor block once and
skip subsequent updates of the same block.

Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index f21fdbf5c75d..7a75e1086961 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1460,6 +1460,7 @@ exit_journal:
                                    EXT4_DESC_PER_BLOCK(sb));
                 int meta_bg = EXT4_HAS_INCOMPAT_FEATURE(sb,
                                 EXT4_FEATURE_INCOMPAT_META_BG);
+                sector_t old_gdb = 0;
 
                 update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
                                sizeof(struct ext4_super_block), 0);
@@ -1467,8 +1468,11 @@ exit_journal:
                         struct buffer_head *gdb_bh;
 
                         gdb_bh = sbi->s_group_desc[gdb_num];
+                        if (old_gdb == gdb_bh->b_blocknr)
+                                continue;
                         update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
                                        gdb_bh->b_size, meta_bg);
+                        old_gdb = gdb_bh->b_blocknr;
                 }
         }
 exit: