ext4: fix long mount times on very big file systems

commit 0548bbb85337e532ca2ed697c3e9b227ff2ed4b4 upstream.

Commit 8aeb00ff85a: "ext4: fix overhead calculation used by
ext4_statfs()" introduced a O(n**2) calculation which makes very large
file systems take forever to mount.  Fix this with an optimization for
non-bigalloc file systems.  (For bigalloc file systems the overhead
needs to be set in the the superblock.)

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 129925a..f8d5fce 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3108,6 +3108,10 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
        ext4_group_t            i, ngroups = ext4_get_groups_count(sb);
        int                     s, j, count = 0;
 
+       if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_BIGALLOC))
+               return (ext4_bg_has_super(sb, grp) + ext4_bg_num_gdb(sb, grp) +
+                       sbi->s_itb_per_group + 2);
+
        first_block = le32_to_cpu(sbi->s_es->s_first_data_block) +
                (grp * EXT4_BLOCKS_PER_GROUP(sb));
        last_block = first_block + EXT4_BLOCKS_PER_GROUP(sb) - 1;