Re: [PATCH v9 09/13] xen: add cache coloring allocator for domains

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.10.2024 11:50, Carlo Nonato wrote:
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -270,6 +270,20 @@ and not running softirqs. Reduce this if softirqs are 
> not being run frequently
>  enough. Setting this to a high value may cause boot failure, particularly if
>  the NMI watchdog is also enabled.
>  
> +### buddy-alloc-size (arm64)
> +> `= <size>`
> +
> +> Default: `64M`
> +
> +Amount of memory reserved for the buddy allocator when colored allocator is
> +active. This options is available only when LLC coloring support is enabled.
> +The colored allocator is meant as an alternative to the buddy allocator,
> +because its allocation policy is by definition incompatible with the generic
> +one. Since the Xen heap systems is not colored yet, we need to support the
> +coexistence of the two allocators for now. This parameter, which is optional
> +and for expert only, it's used to set the amount of memory reserved to the
> +buddy allocator.

Like for the options in patch 1, here I think you also want to make explicit
the dependency on CONFIG_LLC_COLORING.

> @@ -1945,6 +1960,155 @@ static unsigned long avail_heap_pages(
>      return free_pages;
>  }
>  
> +/*************************
> + * COLORED SIDE-ALLOCATOR
> + *
> + * Pages are grouped by LLC color in lists which are globally referred to as 
> the
> + * color heap. Lists are populated in end_boot_allocator().
> + * After initialization there will be N lists where N is the number of
> + * available colors on the platform.
> + */
> +static struct page_list_head *__ro_after_init _color_heap;
> +#define color_heap(color) (&_color_heap[color])
> +
> +static unsigned long *__ro_after_init free_colored_pages;
> +
> +static unsigned long __initdata buddy_alloc_size =
> +    MB(CONFIG_BUDDY_ALLOCATOR_SIZE);
> +size_param("buddy-alloc-size", buddy_alloc_size);
> +
> +/* Memory required for buddy allocator to work with colored one */
> +#ifdef CONFIG_LLC_COLORING
> +#define domain_num_llc_colors(d) (d)->num_llc_colors
> +#define domain_llc_color(d, i)   (d)->llc_colors[i]

I'm uncertain whether Misra would insist on an outer pair of parentheses for
both of these.

Jan