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

[Jianyong Wu]

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.

Thanks
Jianyong