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

[Jianyue Wu]

On Tue, Mar 3, 2026 at 3:43 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> 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.

Sorry about that. I wasn't able to reproduce the issue on my side.
On a closer look, the change seems overly complicated and may not be
worth the risk.
Let's drop this patch for now.