On Thu 30-06-22 02:17:21, Kiselev, Oleg wrote:
> This patch avoids doing an O(n**2)-complexity walk through every flex group.
> Instead, it uses the already computed overhead information for the newly
> allocated space, and simply adds it to the previously calculated
> overhead stored in the superblock. This drastically reduces the time
> taken to resize very large bigalloc filesystems (from 3+ hours for a
> 64TB fs down to milliseconds).
>
> Signed-off-by: Oleg Kiselev <okiselev@xxxxxxxxxx>
> ---
> fs/ext4/resize.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
Overall this looks fine, a few smaller comments below.
>
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index 8b70a4701293..2acc9fca99ea 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -1380,6 +1380,16 @@ static int ext4_setup_new_descs(handle_t *handle, struct super_block *sb,
> return err;
> }
>
> +static void ext4_set_overhead(struct super_block *sb,
> + const ext4_grpblk_t overhead)
> +{
ext4_add_overhead() would be a better name I suppose. Also the 'overhead'
should rather be ext4_fsblk_t to be on the safe side...
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct ext4_super_block *es = sbi->s_es;
Empty line between variable declarations and the code please.
> + sbi->s_overhead += overhead;
> + es->s_overhead_clusters = cpu_to_le32((unsigned long) sbi->s_overhead);
^^^ the typecast looks
bogus here...
> + smp_wmb();
> +}
The barrier without any comment makes me really wonder why it is here...
But I get ext4_calculate_overhead() has is as well so you're just keeping
it.
> +
> /*
> * ext4_update_super() updates the super block so that the newly added
> * groups can be seen by the filesystem.
> @@ -1482,8 +1492,16 @@ static void ext4_update_super(struct super_block *sb,
>
> /*
> * Update the fs overhead information
> + *
> + * For bigalloc, if the superblock already has a properly calculated
> + * overhead, update it wth a value based on numbers already computed
^^ with
> + * above for the newly allocated capacity.
> */
> - ext4_calculate_overhead(sb);
> + if (ext4_has_feature_bigalloc(sb) && (sbi->s_overhead != 0))
> + ext4_set_overhead(sb,
> + EXT4_NUM_B2C(sbi, blocks_count - free_blocks));
> + else
> + ext4_calculate_overhead(sb);
>
> if (test_opt(sb, DEBUG))
> printk(KERN_DEBUG "EXT4-fs: added group %u:"
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
