Re: [PATCH 2/2 v3] mm/compaction: Disable compact_unevictable_allowed on RT

From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH 2/2 v3] mm/compaction: Disable compact_unevictable_allowed on RT
Date: Wed, 4 Mar 2020 09:19:21 +0100	[thread overview]
Message-ID: <bb5bdf8a-67f0-565b-33a1-8cff6f205f2e@suse.cz> (raw)
In-Reply-To: <20200303155635.1955cb90451abd3ef8bfba63@linux-foundation.org>

On 3/4/20 12:56 AM, Andrew Morton wrote:
>> @@ -2572,6 +2577,26 @@ int proc_dointvec(struct ctl_table *table, int write,
>>  	return do_proc_dointvec(table, write, buffer, lenp, ppos, NULL, NULL);
>>  }
>>  
>> +#ifdef CONFIG_COMPACTION
>> +static int proc_dointvec_warn_RT_change(struct ctl_table *table, int write,
>> +					void __user *buffer, size_t *lenp,
>> +					loff_t *ppos)
>> +{
>> +	int ret, old;
>> +
>> +	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write)
>> +		return proc_dointvec(table, write, buffer, lenp, ppos);
>> +
>> +	old = *(int *)table->data;
>> +	ret = proc_dointvec(table, write, buffer, lenp, ppos);
>> +	if (ret)
>> +		return ret;
>> +	WARN_ONCE(old != *(int *)table->data, "sysctl attribute %s changed.",
>> +		  table->procname);
> 
> The WARN will include a stack trace which just isn't interesting.  A
> pr_warn() would be better?

Yeah, the only interesting part of full WARN would possibly be, which process
changed it. That might be useful to print.

>> +	return ret;
>> +}
>> +#endif
> 