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Date: Mon, 22 Apr 2024 17:13:18 +0200
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Subject: Re: [PATCH] mm: Update shuffle documentation to match its current
 state
To: =?UTF-8?Q?Ma=C3=ADra_Canal?= <mcanal@igalia.com>,
 Jonathan Corbet <corbet@lwn.net>, Andrew Morton <akpm@linux-foundation.org>,
 Josh Poimboeuf <jpoimboe@kernel.org>, Tejun Heo <tj@kernel.org>,
 Wei Yang <richard.weiyang@linux.alibaba.com>, Michal Hocko
 <mhocko@suse.com>, Johannes Weiner <hannes@cmpxchg.org>,
 Minchan Kim <minchan@kernel.org>, Huang Ying <ying.huang@intel.com>,
 Mel Gorman <mgorman@techsingularity.net>,
 Dan Williams <dan.j.williams@intel.com>
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org, kernel-dev@igalia.com
References: <20240422142007.1062231-1-mcanal@igalia.com>
From: David Hildenbrand <david@redhat.com>
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In-Reply-To: <20240422142007.1062231-1-mcanal@igalia.com>
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On 22.04.24 16:18, Maíra Canal wrote:
> Commit 839195352d82 ("mm/shuffle: remove dynamic reconfiguration")
> removed the dynamic reconfiguration capabilities from the shuffle page
> allocator. This means that, now, we don't have any perspective of an
> "autodetection of memory-side-cache" that triggers the enablement of the
> shuffle page allocator.

IIRC (it's been a while), we never had that autodetection upstream; we 
only had the code in place that would never get called. 839195352d82 
removed that (dead) code.

> 
> Therefore, let the documentation reflect that the only way to enable
> the shuffle page allocator is by setting `page_alloc.shuffle=1`.
> 
> Signed-off-by: Maíra Canal <mcanal@igalia.com>
> ---
>   Documentation/admin-guide/kernel-parameters.txt | 10 ++++------
>   mm/Kconfig                                      |  7 +++----
>   2 files changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 902ecd92a29f..924bb8ddd8a8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4170,13 +4170,11 @@
>   
>   	page_alloc.shuffle=
>   			[KNL] Boolean flag to control whether the page allocator
> -			should randomize its free lists. The randomization may
> -			be automatically enabled if the kernel detects it is
> -			running on a platform with a direct-mapped memory-side
> -			cache, and this parameter can be used to
> -			override/disable that behavior. The state of the flag
> -			can be read from sysfs at:
> +			should randomize its free lists. This parameter can be
> +			used to enable/disable page randomization. The state of
> +			the flag can be read from sysfs at:
>   			/sys/module/page_alloc/parameters/shuffle.
> +			This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y.
>   
>   	page_owner=	[KNL,EARLY] Boot-time page_owner enabling option.
>   			Storage of the information about who allocated
> diff --git a/mm/Kconfig b/mm/Kconfig
> index b1448aa81e15..f30a18a0e37d 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -333,10 +333,9 @@ config SHUFFLE_PAGE_ALLOCATOR
>   
>   	  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.
> +	  this reason, by default, the randomization is not enabled even
> +	  if SHUFFLE_PAGE_ALLOCATOR=y. The randomization may be force enabled
> +	  with the 'page_alloc.shuffle' kernel command line parameter.
>   
>   	  Say Y if unsure.
>   
Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb