linux-kernel - Re: [PATCH v2 3/3] mm/memcg: introduce mem_cgroup_early

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Message-ID: <xp52maa4uvkgfurxpfbu2bxcajqvlmu4xk7bj7qpiipjtx7sha@vqc6r7lzmley>
Date: Thu, 24 Apr 2025 18:30:55 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Huan Yang <link@...o.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, Petr Mladek <pmladek@...e.com>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Francesco Valla <francesco@...la.it>, 
	Huang Shijie <shijie@...amperecomputing.com>, KP Singh <kpsingh@...nel.org>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	"Uladzislau Rezki (Sony)" <urezki@...il.com>, Guo Weikang <guoweikang.kernel@...il.com>, 
	Raul E Rangel <rrangel@...omium.org>, cgroups@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, Paul Moore <paul@...l-moore.com>, 
	"Mike Rapoport (Microsoft)" <rppt@...nel.org>, opensource.kernel@...o.com
Subject: Re: [PATCH v2 3/3] mm/memcg: introduce mem_cgroup_early_init

On Fri, Apr 25, 2025 at 09:11:01AM +0800, Huan Yang wrote:
> Hi Shakeel
> 
> 在 2025/4/25 07:00, Shakeel Butt 写道:
> > On Thu, Apr 24, 2025 at 09:00:01AM -0700, Shakeel Butt wrote:
> > > On Thu, Apr 24, 2025 at 08:09:29PM +0800, Huan Yang wrote:
> > > > When cgroup_init() creates root_mem_cgroup through css_online callback,
> > > > some critical resources might not be fully initialized, forcing later
> > > > operations to perform conditional checks for resource availability.
> > > > 
> > > > This patch introduces mem_cgroup_early_init() to address the init order,
> > > > it invoke before cgroup_init, so, compare mem_cgroup_init which invoked
> > > > by initcall, mem_cgroup_early_init can use to prepare some key resources
> > > > before root_mem_cgroup alloc.
> > > > 
> > > > Signed-off-by: Huan Yang <link@...o.com>
> > > > Suggested-by: Shakeel Butt <shakeel.butt@...ux.dev>
> > > Please move this patch as the first patch of the series and also remove
> > > the "early" from the function name as it has a different meaning in the
> > > context of cgroup init. Something like either memcg_init() or
> > > memcg_kmem_caches_init().
> > BTW I think just putting this kmem cache creation in mem_cgroup_init()
> > and explicitly calling it before cgroup_init() would be fine. In that
> > case there would be a single memcg init function.
> 
> Maybe someone also need init something after cgroup init done?
> 
> Currently no, but for furture may need?

If that is needed in future then that can be done in future. I would say
simply call mem_cgroup_init() before cgroup_init() for now.