linux-kernel - Re: [PATCH 03/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

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Date:	Thu, 1 Oct 2015 09:35:49 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/10] mm, page_alloc: Remove unnecessary taking of a
 seqlock when cpusets are disabled

On 10/01/2015 12:22 AM, David Rientjes wrote:
> On Mon, 21 Sep 2015, Mel Gorman wrote:
>> @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
>>    */
>>   static inline bool read_mems_allowed_retry(unsigned int seq)
>>   {
>> +	if (!cpusets_enabled())
>> +		return false;
>> +
>>   	return read_seqcount_retry(&current->mems_allowed_seq, seq);
>>   }
>>
>
> I thought this was going to test nr_cpusets() <= 1?

That was another patch in prior iteration of the series, but turns out 
it was unnecessary, because cpusets_enabled() is already only true when 
nr_cpusets() > 1 - see https://lkml.org/lkml/2015/8/25/300
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