Re: [PATCH v4 1/1] mm: optimize stat output for 11% sys time reduce

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, Jan 23, 2026 at 11:01:08PM +0800, Jianyue Wu wrote:
> +void memcg_seq_buf_print_stat(struct seq_buf *s, const char *prefix,
> +			      const char *name, char sep, u64 val)
> +{
> +	char num_buf[MEMCG_DEC_U64_MAX_LEN + 2];  /* +2 for separator and newline */
> +	int num_len;
> +
> +	/* Embed separator at the beginning */
> +	num_buf[0] = sep;
> +
> +	/* Convert number starting at offset 1 */
> +	num_len = num_to_str(num_buf + 1, sizeof(num_buf) - 2, val, 0);
> +	if (num_len <= 0)
> +		return;
> +
> +	/* Embed newline at the end */
> +	num_buf[num_len + 1] = '\n';
> +
> +	if (prefix && *prefix && seq_buf_puts(s, prefix))
> +		return;
> +	if (seq_buf_puts(s, name))
> +		return;
> +	/* Output separator, value, and newline in one call */
> +	seq_buf_putmem(s, num_buf, num_len + 2);

You seem to be losing the \0 somewhere. I'm getting garbage at the end
of memory.stat on mm-new:

  [...]
  thp_swpout_fallback 1212
  hp_swpout_fallback 1212
  hp_swpout_fallback 1054
  907
  1278

Dropping this patch fixes the issue.