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

From: Luis Chamberlain <mcgrof@kernel.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Shakeel Butt <shakeelb@google.com>,
	Muchun Song <muchun.song@linux.dev>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
	Yu Zhao <yuzhao@google.com>, Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	"T.J. Mercier" <tjmercier@google.com>,
	Greg Thelen <gthelen@google.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	cgroups@vger.kernel.org
Subject: Re: [RFC PATCH 7/8] memcg: add sysctl and config option to control memory recharging
Date: Thu, 20 Jul 2023 11:30:49 -0700	[thread overview]
Message-ID: <ZLl9WfMgZSeKtyX7@bombadil.infradead.org> (raw)
In-Reply-To: <CAJD7tkbsZ5rAn5nNUvhuN9uUb4qPcsGZ8pcwCHzbqbajXKP9=g@mail.gmail.com>

On Thu, Jul 20, 2023 at 11:24:20AM -0700, Yosry Ahmed wrote:
> On Thu, Jul 20, 2023 at 11:13 AM Luis Chamberlain <mcgrof@kernel.org> wrote:
> >
> > 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@google.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.
> 
> Thanks for pointing this out, I definitely missed it. Will do that in
> the next version. I guess this will also reduce the reviewer churn if
> I won't be touching kernel/sysctl.c?

Right, it means I don't have to care anymore about random sysctl knobs.
Let people knob it all up.

  Luis