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Subject: Re: [PATCH 3/5] mm/vmalloc.c: correct lazy_max_pages() return value
To: David Rientjes <rientjes@google.com>
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 <alpine.DEB.2.10.1609211418480.20971@chino.kir.corp.google.com>
Cc: zijun_hu@htc.com, Andrew Morton <akpm@linux-foundation.org>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org, tj@kernel.org,
        mingo@kernel.org, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net
From: zijun_hu <zijun_hu@zoho.com>
Message-ID: <3ef46c24-769d-701a-938b-826f4249bf0b@zoho.com>
Date: Thu, 22 Sep 2016 07:30:05 +0800
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On 2016/9/22 5:21, David Rientjes wrote:
> On Wed, 21 Sep 2016, zijun_hu wrote:
> 
>> From: zijun_hu <zijun_hu@htc.com>
>>
>> correct lazy_max_pages() return value if the number of online
>> CPUs is power of 2
>>
>> Signed-off-by: zijun_hu <zijun_hu@htc.com>
>> ---
>>  mm/vmalloc.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index a125ae8..2804224 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -594,7 +594,9 @@ static unsigned long lazy_max_pages(void)
>>  {
>>  	unsigned int log;
>>  
>> -	log = fls(num_online_cpus());
>> +	log = num_online_cpus();
>> +	if (log > 1)
>> +		log = (unsigned int)get_count_order(log);
>>  
>>  	return log * (32UL * 1024 * 1024 / PAGE_SIZE);
>>  }
> 
> The implementation of lazy_max_pages() is somewhat arbitrarily defined, 
> the existing approximation has been around for eight years and 
> num_online_cpus() isn't intended to be rounded up to the next power of 2.  
> I'd be inclined to just leave it as it is.
> 
do i understand the intent in current code logic as below ?
[8, 15) roundup to 16?
[32, 63) roundup to 64?