Re: [PATCH v2 20/23] sched/cache: Add user control to adjust the parameters of cache-aware scheduling

[Chen, Yu C]

Hello Jianyong,

On 1/15/2026 6:03 PM, Jianyong Wu wrote:
> Hello Tim, Chen Yu,
>
> >   static bool exceed_llc_capacity(struct mm_struct *mm, int cpu)
> >   {
> > +    unsigned int llc, scale;
> >       struct cacheinfo *ci;
> >       unsigned long rss;
> > -    unsigned int llc;
> >       /*
> >        * get_cpu_cacheinfo_level() can not be used
> > @@ -1252,19 +1266,54 @@ static bool exceed_llc_capacity(struct 
> > mm_struct *mm, int cpu)
> >       rss = get_mm_counter(mm, MM_ANONPAGES) +
> >           get_mm_counter(mm, MM_SHMEMPAGES);
> > -    return (llc <= (rss * PAGE_SIZE));
> > +    /*
> > +     * Scale the LLC size by 256*llc_aggr_tolerance
> > +     * and compare it to the task's RSS size.
> > +     *
> > +     * Suppose the L3 size is 32MB. If the
> > +     * llc_aggr_tolerance is 1:
> > +     * When the RSS is larger than 32MB, the process
> > +     * is regarded as exceeding the LLC capacity. If
> > +     * the llc_aggr_tolerance is 99:
> > +     * When the RSS is larger than 784GB, the process
> > +     * is regarded as exceeding the LLC capacity because:
> > +     * 784GB = (1 + (99 - 1) * 256) * 32MB
> > +     */
> > +    scale = get_sched_cache_scale(256);
> > +    if (scale == INT_MAX)
> > +        return false;
> > +
> > +    return ((llc * scale) <= (rss * PAGE_SIZE));
> >   }
> Suppose the LLC is 16 MB (which is 16777216 bytes). If we set 
> `llc_aggr_tolerance` to 99, the `scale` value will be 25089. When 
> calculating `16777216 * 25089`, the result is 420923572224, which 
> exceeds 2^32 and thus causes an integer overflow.

[resend might be due to smtp issue]
Good catch! Let me switch it to u64, it should be big enough for
llc size(max to about (2^64 -1)/2589 bytes)

thanks,
Chenyu