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>

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index f21fdbf5c75df946f7dcf64e1d29e87ff42061b9..7a75e1086961eedb674b8c2bf1bb84e657f4dfa2 100644 (file)
--- 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: