On 2011-07-06, at 10:35 AM, Theodore Ts'o wrote:
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> ---
> fs/ext4/super.c | 37 ++++++++++++++++++++++++-------------
> 1 files changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index a803d65..7a4d54e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4529,16 +4529,34 @@ restore_opts:
> return err;
> }
>
> +/*
> + * Note: calculating the overhead so we can be compatible with
> + * historical BSD practice is quite difficult in the face of
> + * clusters/bigalloc. This is because multiple metadata blocks from
> + * different block group can end up in the same allocation cluster.
> + * Calculating the exact overhead in the face of clustered allocation
> + * requires either O(all block bitmaps) in memory or O(number of block
> + * groups**2) in time. We will still calculate the superblock for
> + * older file systems --- and if we come across with a bigalloc file
> + * system with zero in s_overhead_clusters the estimate will be close to
> + * correct especially for very large cluster sizes --- but for newer
> + * file systems, it's better to calculate this figure once at mkfs
> + * time, and store it in the superblock. If the superblock value is
> + * present (even for non-bigalloc file systems), we will use it.
> + */
> static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
> {
> struct super_block *sb = dentry->d_sb;
> struct ext4_sb_info *sbi = EXT4_SB(sb);
> struct ext4_super_block *es = sbi->s_es;
> + struct ext4_group_desc *gdp;
> u64 fsid;
> s64 bfree;
>
> if (test_opt(sb, MINIX_DF)) {
Should we change this check to unlikely()?
> sbi->s_overhead_last = 0;
> + } else if (es->s_overhead_clusters) {
> + sbi->s_overhead_last = le32_to_cpu(es->s_overhead_clusters);
> } else if (sbi->s_blocks_last != ext4_blocks_count(es)) {
> ext4_group_t i, ngroups = ext4_get_groups_count(sb);
> ext4_fsblk_t overhead = 0;
> @@ -4553,24 +4571,16 @@ static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
> * All of the blocks before first_data_block are
> * overhead
> */
> - overhead = le32_to_cpu(es->s_first_data_block);
> + overhead = EXT4_B2C(sbi, le32_to_cpu(es->s_first_data_block));
>
> /*
> - * Add the overhead attributed to the superblock and
> - * block group descriptors. If the sparse superblocks
> - * feature is turned on, then not all groups have this.
> + * Add the overhead found in each block group
> */
> for (i = 0; i < ngroups; i++) {
> - overhead += ext4_bg_has_super(sb, i) +
> - ext4_bg_num_gdb(sb, i);
> + gdp = ext4_get_group_desc(sb, i, NULL);
> + overhead += ext4_num_overhead_clusters(sb, i, gdp);
> cond_resched();
> }
> -
> - /*
> - * Every block group has an inode bitmap, a block
> - * bitmap, and an inode table.
> - */
> - overhead += ngroups * (2 + sbi->s_itb_per_group);
> sbi->s_overhead_last = overhead;
> smp_wmb();
> sbi->s_blocks_last = ext4_blocks_count(es);
> @@ -4578,7 +4588,8 @@ static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
>
> buf->f_type = EXT4_SUPER_MAGIC;
> buf->f_bsize = sb->s_blocksize;
> - buf->f_blocks = ext4_blocks_count(es) - sbi->s_overhead_last;
> + buf->f_blocks = (ext4_blocks_count(es) -
> + EXT4_C2B(sbi, sbi->s_overhead_last));
> bfree = percpu_counter_sum_positive(&sbi->s_freeclusters_counter) -
> percpu_counter_sum_positive(&sbi->s_dirtyclusters_counter);
> /* prevent underflow in case that few free space is available */
> --
> 1.7.4.1.22.gec8e1.dirty
>
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Cheers, Andreas
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