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Date:   Thu, 24 Nov 2022 20:33:12 +0900
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Pekka Enberg <penberg@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>, patches@lists.linux.dev,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/12] mm, slub: add CONFIG_SLUB_TINY
Message-ID: <Y39WeEpboF4u7pP6@hyeyoo>
References: <20221121171202.22080-1-vbabka@suse.cz>
 <20221121171202.22080-3-vbabka@suse.cz>
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On Mon, Nov 21, 2022 at 06:11:52PM +0100, Vlastimil Babka wrote:
> For tiny systems that have used SLOB until now, SLUB might be
> impractical due to its higher memory usage. To help with that, introduce
> an option CONFIG_SLUB_TINY that modifies SLUB to use less memory.
> This is done by sacrificing scalability, security and debugging
> features, therefore not recommended for any system with more than 16MB
> RAM.
> 
> This commit introduces the option and uses it to set other related
> options in a way that reduces memory usage.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/Kconfig       | 21 +++++++++++++++++----
>  mm/Kconfig.debug |  2 +-
>  2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 57e1d8c5b505..5941cb34e30d 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -230,6 +230,19 @@ config SLOB
>  
>  endchoice
>  
> +config SLUB_TINY
> +	bool "Configure SLUB for minimal memory footprint"
> +	depends on SLUB && EXPERT
> +	select SLAB_MERGE_DEFAULT
> +	help
> +	   Configures the SLUB allocator in a way to achieve minimal memory
> +	   footprint, sacrificing scalability, debugging and other features.
> +	   This is intended only for the smallest system that had used the
> +	   SLOB allocator and is not recommended for systems with more than
> +	   16MB RAM.
> +
> +	   If unsure, say N.
> +
>  config SLAB_MERGE_DEFAULT
>  	bool "Allow slab caches to be merged"
>  	default y
> @@ -247,7 +260,7 @@ config SLAB_MERGE_DEFAULT
>  
>  config SLAB_FREELIST_RANDOM
>  	bool "Randomize slab freelist"
> -	depends on SLAB || SLUB
> +	depends on SLAB || SLUB && !SLUB_TINY
>  	help
>  	  Randomizes the freelist order used on creating new pages. This
>  	  security feature reduces the predictability of the kernel slab
> @@ -255,7 +268,7 @@ config SLAB_FREELIST_RANDOM
>  
>  config SLAB_FREELIST_HARDENED
>  	bool "Harden slab freelist metadata"
> -	depends on SLAB || SLUB
> +	depends on SLAB || SLUB && !SLUB_TINY
>  	help
>  	  Many kernel heap attacks try to target slab cache metadata and
>  	  other infrastructure. This options makes minor performance
> @@ -267,7 +280,7 @@ config SLAB_FREELIST_HARDENED
>  config SLUB_STATS
>  	default n
>  	bool "Enable SLUB performance statistics"
> -	depends on SLUB && SYSFS
> +	depends on SLUB && SYSFS && !SLUB_TINY
>  	help
>  	  SLUB statistics are useful to debug SLUBs allocation behavior in
>  	  order find ways to optimize the allocator. This should never be
> @@ -279,7 +292,7 @@ config SLUB_STATS
>  
>  config SLUB_CPU_PARTIAL
>  	default y
> -	depends on SLUB && SMP
> +	depends on SLUB && SMP && !SLUB_TINY
>  	bool "SLUB per cpu partial cache"
>  	help
>  	  Per cpu partial caches accelerate objects allocation and freeing
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index ce8dded36de9..fca699ad1fb0 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -56,7 +56,7 @@ config DEBUG_SLAB
>  config SLUB_DEBUG
>  	default y
>  	bool "Enable SLUB debugging support" if EXPERT
> -	depends on SLUB && SYSFS
> +	depends on SLUB && SYSFS && !SLUB_TINY
>  	select STACKDEPOT if STACKTRACE_SUPPORT
>  	help
>  	  SLUB has extensive debug support features. Disabling these can
> -- 
> 2.38.1

Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

small comment:
SLAB || (SLUB && !SLUB_TINY) would be easier to interpret than
SLAB || SLUB && !SLUB_TINY

-- 
Thanks,
Hyeonggon