Re: [PATCH v1] ext4: add mb_stats_clear for mballoc statistics

[Zhang Yi]

On 4/14/2026 6:02 PM, Baolin Liu wrote:
> From: Baolin Liu <liubaolin@xxxxxxxxxx>
> 
> Add a write-only mb_stats_clear sysfs knob to reset ext4 mballoc
> runtime statistics.This makes it easier to inspect allocator
> activity for a specific workload instead of using counters
> accumulated since mount.
> 
> Signed-off-by: Baolin Liu <liubaolin@xxxxxxxxxx>

Looks good to me!

Reviewed-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

> ---
>  fs/ext4/ext4.h    |  1 +
>  fs/ext4/mballoc.c | 31 +++++++++++++++++++++++++++++++
>  fs/ext4/sysfs.c   | 24 ++++++++++++++++++++++++
>  3 files changed, 56 insertions(+)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 7617e2d454ea..3a32e1a515dd 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2995,6 +2995,7 @@ 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 bb58eafb87bc..382c91586b26 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3219,6 +3219,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
>  	}
>  	seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
>  	seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));
> +	seq_printf(seq, "\tblocks_allocated: %u\n",
> +		   atomic_read(&sbi->s_bal_allocated));
>  
>  	seq_printf(seq, "\tgroups_scanned: %u\n",
>  		   atomic_read(&sbi->s_bal_groups_scanned));
> @@ -4721,6 +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 923b375e017f..a5bd88a99f22 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -41,6 +41,7 @@ typedef enum {
>  	attr_pointer_atomic,
>  	attr_journal_task,
>  	attr_err_report_sec,
> +	attr_mb_stats_clear,
>  } attr_id_t;
>  
>  typedef enum {
> @@ -161,6 +162,25 @@ static ssize_t err_report_sec_store(struct ext4_sb_info *sbi,
>  	return count;
>  }
>  
> +static ssize_t mb_stats_clear_store(struct ext4_sb_info *sbi,
> +				    const char *buf, size_t count)
> +{
> +	int val;
> +	int ret;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	ret = kstrtoint(skip_spaces(buf), 0, &val);
> +	if (ret)
> +		return ret;
> +	if (val != 1)
> +		return -EINVAL;
> +
> +	ext4_mb_stats_clear(sbi);
> +	return count;
> +}
> +
>  static ssize_t journal_task_show(struct ext4_sb_info *sbi, char *buf)
>  {
>  	if (!sbi->s_journal)
> @@ -251,6 +271,7 @@ EXT4_ATTR_OFFSET(mb_best_avail_max_trim_order, 0644, mb_order,
>  EXT4_ATTR_OFFSET(err_report_sec, 0644, err_report_sec, ext4_sb_info, s_err_report_sec);
>  EXT4_RW_ATTR_SBI_UI(inode_goal, s_inode_goal);
>  EXT4_RW_ATTR_SBI_UI(mb_stats, s_mb_stats);
> +EXT4_ATTR(mb_stats_clear, 0200, mb_stats_clear);
>  EXT4_RW_ATTR_SBI_UI(mb_max_to_scan, s_mb_max_to_scan);
>  EXT4_RW_ATTR_SBI_UI(mb_min_to_scan, s_mb_min_to_scan);
>  EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
> @@ -301,6 +322,7 @@ static struct attribute *ext4_attrs[] = {
>  	ATTR_LIST(inode_readahead_blks),
>  	ATTR_LIST(inode_goal),
>  	ATTR_LIST(mb_stats),
> +	ATTR_LIST(mb_stats_clear),
>  	ATTR_LIST(mb_max_to_scan),
>  	ATTR_LIST(mb_min_to_scan),
>  	ATTR_LIST(mb_order2_req),
> @@ -561,6 +583,8 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
>  		return trigger_test_error(sbi, buf, len);
>  	case attr_err_report_sec:
>  		return err_report_sec_store(sbi, buf, len);
> +	case attr_mb_stats_clear:
> +		return mb_stats_clear_store(sbi, buf, len);
>  	default:
>  		return ext4_generic_attr_store(a, sbi, buf, len);
>  	}