[ 39/95] ext4: fix long mount times on very big file systems

[Ben Hutchings]

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@xxxxxxx>

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@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/ext4/super.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 56bcaec..5984989 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3120,6 +3120,10 @@ 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;


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