linux-kernel - Re: [RFC PATCH 7/8] memcg: add sysctl and config option to control memory recharging

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Message-ID: <ZLl5XA25BIlYyngD@bombadil.infradead.org>
Date:   Thu, 20 Jul 2023 11:13:48 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Yu Zhao <yuzhao@...gle.com>, Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        "T.J. Mercier" <tjmercier@...gle.com>,
        Greg Thelen <gthelen@...gle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH 7/8] memcg: add sysctl and config option to control
 memory recharging

On Thu, Jul 20, 2023 at 07:08:24AM +0000, Yosry Ahmed wrote:
> Add a sysctl to enable/disable memory recharging for offline memcgs. Add
> a config option to control whether or not it is enabled by default.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
>  include/linux/memcontrol.h |  2 ++
>  kernel/sysctl.c            | 11 +++++++++++
>  mm/Kconfig                 | 12 ++++++++++++
>  mm/memcontrol.c            |  9 ++++++++-
>  4 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 59b653d4a76e..ae9f09ee90cb 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -60,6 +60,8 @@ struct mem_cgroup_reclaim_cookie {
>  
>  #ifdef CONFIG_MEMCG
>  
> +extern int sysctl_recharge_offline_memcgs;
> +
>  #define MEM_CGROUP_ID_SHIFT	16
>  #define MEM_CGROUP_ID_MAX	USHRT_MAX
>  
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 354a2d294f52..1735d1d95652 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2249,6 +2249,17 @@ static struct ctl_table vm_table[] = {
>  		.extra2		= (void *)&mmap_rnd_compat_bits_max,
>  	},
>  #endif
> +#ifdef CONFIG_MEMCG
> +	{
> +		.procname	= "recharge_offline_memcgs",
> +		.data		= &sysctl_recharge_offline_memcgs,
> +		.maxlen		= sizeof(sysctl_recharge_offline_memcgs),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= SYSCTL_ONE,
> +	},
> +#endif /* CONFIG_MEMCG */
>  	{ }
>  };

Please don't add any more sysctls to kernel/sysctl.c, git log that file
for a series of cleanups which show how to use your own and why we have
been doing that cleanup.

  Luis