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Subject: Re: [PATCH] mm, slub: remove slub_memcg_sysfs boot param and
 CONFIG_SLUB_MEMCG_SYSFS_ON
To:     Vlastimil Babka <vbabka@suse.cz>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Roman Gushchin <guro@fb.com>
References: <20210127124745.7928-1-vbabka@suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <8f989256-9e43-1747-4de5-fa46db0d7f7e@redhat.com>
Date:   Wed, 27 Jan 2021 14:59:12 +0100
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On 27.01.21 13:47, Vlastimil Babka wrote:
> The boot param and config determine the value of memcg_sysfs_enabled, which is
> unused since commit 10befea91b61 ("mm: memcg/slab: use a single set of
> kmem_caches for all allocations") as there are no per-memcg kmem caches
> anymore.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>   Documentation/admin-guide/kernel-parameters.txt |  8 --------
>   init/Kconfig                                    | 14 --------------
>   mm/slub.c                                       | 16 ----------------
>   3 files changed, 38 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f4497faef266..7dc351da0005 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4892,14 +4892,6 @@
>   			last alloc / free. For more information see
>   			Documentation/vm/slub.rst.
>   
> -	slub_memcg_sysfs=	[MM, SLUB]
> -			Determines whether to enable sysfs directories for
> -			memory cgroup sub-caches. 1 to enable, 0 to disable.
> -			The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
> -			Enabling this can lead to a very high number of	debug
> -			directories and files being created under
> -			/sys/kernel/slub.
> -
>   	slub_max_order= [MM, SLUB]
>   			Determines the maximum allowed order for slabs.
>   			A high setting may cause OOMs due to memory
> diff --git a/init/Kconfig b/init/Kconfig
> index e4e2932da237..af454a51f3c5 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1851,20 +1851,6 @@ config SLUB_DEBUG
>   	  SLUB sysfs support. /sys/slab will not exist and there will be
>   	  no support for cache validation etc.
>   
> -config SLUB_MEMCG_SYSFS_ON
> -	default n
> -	bool "Enable memcg SLUB sysfs support by default" if EXPERT
> -	depends on SLUB && SYSFS && MEMCG
> -	help
> -	  SLUB creates a directory under /sys/kernel/slab for each
> -	  allocation cache to host info and debug files. If memory
> -	  cgroup is enabled, each cache can have per memory cgroup
> -	  caches. SLUB can create the same sysfs directories for these
> -	  caches under /sys/kernel/slab/CACHE/cgroup but it can lead
> -	  to a very high number of debug files being created. This is
> -	  controlled by slub_memcg_sysfs boot parameter and this
> -	  config option determines the parameter's default value.
> -
>   config COMPAT_BRK
>   	bool "Disable heap randomization"
>   	default y
> diff --git a/mm/slub.c b/mm/slub.c
> index 1b5148747c64..88782727412c 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5040,22 +5040,6 @@ enum slab_stat_type {
>   #define SO_OBJECTS	(1 << SL_OBJECTS)
>   #define SO_TOTAL	(1 << SL_TOTAL)
>   
> -#ifdef CONFIG_MEMCG
> -static bool memcg_sysfs_enabled = IS_ENABLED(CONFIG_SLUB_MEMCG_SYSFS_ON);
> -
> -static int __init setup_slub_memcg_sysfs(char *str)
> -{
> -	int v;
> -
> -	if (get_option(&str, &v) > 0)
> -		memcg_sysfs_enabled = v;
> -
> -	return 1;
> -}
> -
> -__setup("slub_memcg_sysfs=", setup_slub_memcg_sysfs);
> -#endif
> -
>   static ssize_t show_slab_objects(struct kmem_cache *s,
>   				 char *buf, unsigned long flags)
>   {
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb