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Subject: Re: [PATCH 03/10] mm, page_alloc: Remove unnecessary taking of a
 seqlock when cpusets are disabled
To: David Rientjes <rientjes@google.com>,
        Mel Gorman <mgorman@techsingularity.net>
References: <1442832762-7247-1-git-send-email-mgorman@techsingularity.net>
 <1442832762-7247-4-git-send-email-mgorman@techsingularity.net>
 <alpine.DEB.2.10.1509301521380.23324@chino.kir.corp.google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Rik van Riel <riel@redhat.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Michal Hocko <mhocko@kernel.org>,
        Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <560CE255.80303@suse.cz>
Date: Thu, 1 Oct 2015 09:35:49 +0200
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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