linux-kernel - Re: [PATCH v4 3/4] mm/page_owner: Print memcg information

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Message-ID: <YfvOp5VXrxy9IW1w@dhcp22.suse.cz>
Date:   Thu, 3 Feb 2022 13:46:31 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Ira Weiny <ira.weiny@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <guro@...com>, Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH v4 3/4] mm/page_owner: Print memcg information

On Wed 02-02-22 15:30:35, Waiman Long wrote:
[...]
> +#ifdef CONFIG_MEMCG
> +	unsigned long memcg_data;
> +	struct mem_cgroup *memcg;
> +	bool online;
> +	char name[80];
> +
> +	rcu_read_lock();
> +	memcg_data = READ_ONCE(page->memcg_data);
> +	if (!memcg_data)
> +		goto out_unlock;
> +
> +	if (memcg_data & MEMCG_DATA_OBJCGS)
> +		ret += scnprintf(kbuf + ret, count - ret,
> +				"Slab cache page\n");
> +
> +	memcg = page_memcg_check(page);
> +	if (!memcg)
> +		goto out_unlock;
> +
> +	online = (memcg->css.flags & CSS_ONLINE);
> +	cgroup_name(memcg->css.cgroup, name, sizeof(name));

Is there any specific reason to use another buffer allocated on the
stack? Also 80B seems too short to cover NAME_MAX.

Nothing else jumped at me.
-- 
Michal Hocko
SUSE Labs