linux-kernel - Re: [PATCH v2] mm/compaction: remove unused variable sysctl_compact

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Date:   Thu, 4 Mar 2021 11:57:35 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Pintu Kumar <pintu@...eaurora.org>, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, iamjoonsoo.kim@....com,
        sh_def@....com, mateusznosek0@...il.com, bhe@...hat.com,
        nigupta@...dia.com, yzaikin@...gle.com, keescook@...omium.org,
        mcgrof@...nel.org, mgorman@...hsingularity.net
Cc:     pintu.ping@...il.com
Subject: Re: [PATCH v2] mm/compaction: remove unused variable
 sysctl_compact_memory

On 3/4/21 11:03 AM, Pintu Kumar wrote:
> The sysctl_compact_memory is mostly unused in mm/compaction.c
> It just acts as a place holder for sysctl to store .data.
> 
> But the .data itself is not needed here.
> So we can get ride of this variable completely and make .data as NULL.
> This will also eliminate the extern declaration from header file.
> No functionality is broken or changed this way.
> 
> Signed-off-by: Pintu Kumar <pintu@...eaurora.org>
> Signed-off-by: Pintu Agarwal <pintu.ping@...il.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
> v2: completely get rid of this variable and set .data to NULL
>     Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> 
>  include/linux/compaction.h | 1 -
>  kernel/sysctl.c            | 2 +-
>  mm/compaction.c            | 3 ---
>  3 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index ed4070e..4221888 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -81,7 +81,6 @@ static inline unsigned long compact_gap(unsigned int order)
>  }
>  
>  #ifdef CONFIG_COMPACTION
> -extern int sysctl_compact_memory;
>  extern unsigned int sysctl_compaction_proactiveness;
>  extern int sysctl_compaction_handler(struct ctl_table *table, int write,
>  			void *buffer, size_t *length, loff_t *ppos);
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index c9fbdd8..07ef240 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2856,7 +2856,7 @@ static struct ctl_table vm_table[] = {
>  #ifdef CONFIG_COMPACTION
>  	{
>  		.procname	= "compact_memory",
> -		.data		= &sysctl_compact_memory,
> +		.data		= NULL,
>  		.maxlen		= sizeof(int),
>  		.mode		= 0200,
>  		.proc_handler	= sysctl_compaction_handler,
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 190ccda..ede2886 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2650,9 +2650,6 @@ static void compact_nodes(void)
>  		compact_node(nid);
>  }
>  
> -/* The written value is actually unused, all memory is compacted */
> -int sysctl_compact_memory;
> -
>  /*
>   * Tunable for proactive compaction. It determines how
>   * aggressively the kernel should compact memory in the
>