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Date: Tue, 2 May 2023 13:50:08 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: wenyang.linux@foxmail.com, Oscar Salvador <osalvador@suse.de>, William
 Lam <william.lam@bytedance.com>, Pintu Kumar <pintu@codeaurora.org>, Fu Wei
 <wefu@redhat.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm: compaction: optimize compact_memory to comply
 with the admin-guide
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On Fri, 28 Apr 2023 11:58:48 +0100 Mel Gorman <mgorman@techsingularity.net> wrote:

> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -1736,6 +1736,7 @@ static int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNE
> >   */
> >  static unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
> >  static int sysctl_extfrag_threshold = 500;
> > +static int sysctl_compact_memory;
> >  
> 
> __read_mostly but that aside, it's only used in
> sysctl_compaction_handler so could also be declared as static within
> that function. That way if CONFIG_SYSCTL is not set, it should be
> guaranteed that the compiler does not save storage for it.

but

static struct ctl_table vm_compaction[] = {
	{
		.procname	= "compact_memory",
		.data		= &sysctl_compact_memory,
		.maxlen		= sizeof(int),
		.mode		= 0200,
		.proc_handler	= sysctl_compaction_handler,
	},


I'll add the __read_mostly, thanks.