Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Andreas Dilger]

On Apr 19, 2026, at 00:34, Baolin Liu <liubaolin12138@xxxxxxx> wrote:
> 
> From: Baolin Liu <liubaolin@xxxxxxxxxx>
> 
> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
> mballoc statistics when 0 is written.
> 
> Signed-off-by: Baolin Liu <liubaolin@xxxxxxxxxx>

Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx <mailto:adilger@xxxxxxxxx>>

> ---
> fs/ext4/ext4.h    |  1 +
> fs/ext4/mballoc.c | 29 +++++++++++++++++++++++++++++
> fs/ext4/sysfs.c   | 40 ++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 68 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 293f698b7042..3223e73612ae 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2994,6 +2994,7 @@ int ext4_fc_record_regions(struct super_block *sb, int ino,
> extern const struct seq_operations ext4_mb_seq_groups_ops;
> extern const struct seq_operations ext4_mb_seq_structs_summary_ops;
> extern int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset);
> +extern void ext4_mb_stats_clear(struct ext4_sb_info *sbi);
> extern int ext4_mb_init(struct super_block *);
> extern void ext4_mb_release(struct super_block *);
> extern ext4_fsblk_t ext4_mb_new_blocks(handle_t *,
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 1e13ef62cb9d..79ddfa935813 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4723,6 +4723,35 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
> trace_ext4_mballoc_prealloc(ac);
> }
> 
> +void ext4_mb_stats_clear(struct ext4_sb_info *sbi)
> +{
> +	int i;
> +
> +	atomic_set(&sbi->s_bal_reqs, 0);
> +	atomic_set(&sbi->s_bal_success, 0);
> +	atomic_set(&sbi->s_bal_allocated, 0);
> +	atomic_set(&sbi->s_bal_groups_scanned, 0);
> +
> +	for (i = 0; i < EXT4_MB_NUM_CRS; i++) {
> +		atomic64_set(&sbi->s_bal_cX_hits[i], 0);
> +		atomic64_set(&sbi->s_bal_cX_groups_considered[i], 0);
> +		atomic_set(&sbi->s_bal_cX_ex_scanned[i], 0);
> +		atomic64_set(&sbi->s_bal_cX_failed[i], 0);
> +	}
> +
> +	atomic_set(&sbi->s_bal_ex_scanned, 0);
> +	atomic_set(&sbi->s_bal_goals, 0);
> +	atomic_set(&sbi->s_bal_stream_goals, 0);
> +	atomic_set(&sbi->s_bal_len_goals, 0);
> +	atomic_set(&sbi->s_bal_2orders, 0);
> +	atomic_set(&sbi->s_bal_breaks, 0);
> +	atomic_set(&sbi->s_mb_lost_chunks, 0);
> +	atomic_set(&sbi->s_mb_buddies_generated, 0);
> +	atomic64_set(&sbi->s_mb_generation_time, 0);
> +	atomic_set(&sbi->s_mb_preallocated, 0);
> +	atomic_set(&sbi->s_mb_discarded, 0);
> +}
> +
> /*
>  * Called on failure; free up any blocks from the inode PA for this
>  * context.  We don't need this for MB_GROUP_PA because we only change
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index b87d7bdab06a..e90885d470ab 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -52,6 +52,42 @@ typedef enum {
> static const char proc_dirname[] = "fs/ext4";
> static struct proc_dir_entry *ext4_proc_root;
> 
> +static int ext4_mb_stats_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, ext4_seq_mb_stats_show, pde_data(inode));
> +}
> +
> +static ssize_t ext4_mb_stats_write(struct file *file, const char __user *buf,
> +				   size_t count, loff_t *ppos)
> +{
> +	struct super_block *sb = pde_data(file_inode(file));
> +	char kbuf[2];
> +
> +	if (count == 0 || count > sizeof(kbuf))
> +		return -EINVAL;
> +
> +	if (copy_from_user(kbuf, buf, count))
> +		return -EFAULT;
> +
> +	if (count == 2) {
> +		if (kbuf[0] != '0' || kbuf[1] != '\n')
> +			return -EINVAL;
> +	} else if (kbuf[0] != '0') {
> +		return -EINVAL;
> +	}
> +
> +	ext4_mb_stats_clear(EXT4_SB(sb));
> +	return count;
> +}
> +
> +static const struct proc_ops ext4_mb_stats_proc_ops = {
> +	.proc_open	= ext4_mb_stats_open,
> +	.proc_read	= seq_read,
> +	.proc_lseek	= seq_lseek,
> +	.proc_release	= single_release,
> +	.proc_write	= ext4_mb_stats_write,
> +};
> +
>  struct ext4_attr {
>  	struct attribute attr;
>  	short attr_id;
> @@ -630,8 +666,8 @@ int ext4_register_sysfs(struct super_block *sb)
>  					ext4_fc_info_show, sb);
>  		proc_create_seq_data("mb_groups", S_IRUGO, sbi->s_proc,
>  				&ext4_mb_seq_groups_ops, sb);
> -		proc_create_single_data("mb_stats", 0444, sbi->s_proc,
> -				ext4_seq_mb_stats_show, sb);
> +		proc_create_data("mb_stats", 0644, sbi->s_proc,
> +				 &ext4_mb_stats_proc_ops, sb);
>  		proc_create_seq_data("mb_structs_summary", 0444, sbi->s_proc,
>  				&ext4_mb_seq_structs_summary_ops, sb);
> }
> -- 
> 2.51.0
> 


Cheers, Andreas