Re: [PATCH v10 1/3] mm: Shuffle initial free memory to improve memory-side-cache utilization

[Vlastimil Babka]

On 2/1/19 6:15 AM, Dan Williams wrote:
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1714,6 +1714,29 @@ config SLAB_FREELIST_HARDENED
>  	  sacrifies to harden the kernel slab allocator against common
>  	  freelist exploit methods.
>  
> +config SHUFFLE_PAGE_ALLOCATOR
> +	bool "Page allocator randomization"
> +	default SLAB_FREELIST_RANDOM && ACPI_NUMA
> +	help
> +	  Randomization of the page allocator improves the average
> +	  utilization of a direct-mapped memory-side-cache. See section
> +	  5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
> +	  6.2a specification for an example of how a platform advertises
> +	  the presence of a memory-side-cache. There are also incidental
> +	  security benefits as it reduces the predictability of page
> +	  allocations to compliment SLAB_FREELIST_RANDOM, but the
> +	  default granularity of shuffling on 4MB (MAX_ORDER) pages is
> +	  selected based on cache utilization benefits.
> +
> +	  While the randomization improves cache utilization it may
> +	  negatively impact workloads on platforms without a cache. For
> +	  this reason, by default, the randomization is enabled only
> +	  after runtime detection of a direct-mapped memory-side-cache.
> +	  Otherwise, the randomization may be force enabled with the
> +	  'page_alloc.shuffle' kernel command line parameter.
> +
> +	  Say Y if unsure.

It says "Say Y if unsure", yet if I run make oldconfig, the default is
N. Does that make sense?

> Page allocator randomization (SHUFFLE_PAGE_ALLOCATOR) [N/y/?] (NEW)