Re: [PATCH v10 1/3] mm: Shuffle initial free memory to improve memory-side-cache utilization
- Date: Fri, 31 May 2019 09:33:36 +0200
- From: Vlastimil Babka <vbabka@xxxxxxx>
- Subject: Re: [PATCH v10 1/3] mm: Shuffle initial free memory to improve memory-side-cache utilization
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)