linux-kernel - Re: [PATCH v2] mm: compaction: optimize compact

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Message-Id: <20230502135008.cb8cc8475971d190d32e699a@linux-foundation.org>
Date:   Tue, 2 May 2023 13:50:08 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     wenyang.linux@...mail.com, Oscar Salvador <osalvador@...e.de>,
        William Lam <william.lam@...edance.com>,
        Pintu Kumar <pintu@...eaurora.org>, Fu Wei <wefu@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: compaction: optimize compact_memory to comply
 with the admin-guide

On Fri, 28 Apr 2023 11:58:48 +0100 Mel Gorman <mgorman@...hsingularity.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.