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Date:   Tue, 8 Aug 2023 09:29:54 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Roman Gushchin <roman.gushchin@linux.dev>
Cc:     xiongwei.song@windriver.com, hannes@cmpxchg.org,
        shakeelb@google.com, muchun.song@linux.dev,
        akpm@linux-foundation.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/memcontrol: add tips for kmem.slabinfo
Message-ID: <ZNHu8m3h3ckn+HeI@dhcp22.suse.cz>
References: <20230808022229.1560559-1-xiongwei.song@windriver.com>
 <ZNG9vwg1K6fn1SvN@P9FQF9L96D>
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On Mon 07-08-23 20:59:59, Roman Gushchin wrote:
> On Tue, Aug 08, 2023 at 10:22:29AM +0800, xiongwei.song@windriver.com wrote:
> > From: Xiongwei Song <xiongwei.song@windriver.com>
> > 
> > No any output from kmem.slabinfo, which is not friendly. Adding
> > tips for it.
> > 
> > Signed-off-by: Xiongwei Song <xiongwei.song@windriver.com>
> > ---
> >  mm/memcontrol.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index e8ca4bdcb03c..58d3bd93890b 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -5002,10 +5002,8 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
> >  #if defined(CONFIG_MEMCG_KMEM) && (defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG))
> >  static int mem_cgroup_slab_show(struct seq_file *m, void *p)
> >  {
> > -	/*
> > -	 * Deprecated.
> > -	 * Please, take a look at tools/cgroup/memcg_slabinfo.py .
> > -	 */
> > +	seq_puts(m, "This file is deprecated.\n"
> > +		"Please use tools/cgroup/memcg_slabinfo.py, which is in kernel source.\n");
> 
> It'll break the ABI.

Agreed

> The only possible option here is to use WARN_ON_ONCE(), which will print once to dmesg.
> But honestly I'm not sure we need it.

There are systems with panic_on_warn configured. I do not think we want
those to go down just becasue some random tool tries to read this file.
-- 
Michal Hocko
SUSE Labs