linux-kernel - Re: [PATCH v13 9/9] lib/nodemask: Optimize node_random for nodemask with single NUMA node

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Message-ID: <51770b88-fbf1-52e7-6d40-666e1fcfb0f2@linux.ibm.com>
Date:   Tue, 9 Aug 2022 11:13:15 +0530
From:   Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com
Subject: Re: [PATCH v13 9/9] lib/nodemask: Optimize node_random for nodemask
 with single NUMA node

On 8/9/22 8:43 AM, Huang, Ying wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
> 
>> The most common case for certain node_random usage (demotion nodemask) is with
>> nodemask weight 1. We can avoid calling get_random_init() in that case and
>> always return the only node set in the nodemask.
> 
> I think that this patch can sit between [5/9] and [6/9], just after it
> is used.
> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
>> ---
>>  lib/nodemask.c | 15 ++++++++++++---
>>  1 file changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/nodemask.c b/lib/nodemask.c
>> index e22647f5181b..c91a6b0404a5 100644
>> --- a/lib/nodemask.c
>> +++ b/lib/nodemask.c
>> @@ -20,12 +20,21 @@ EXPORT_SYMBOL(__next_node_in);
>>   */
>>  int node_random(const nodemask_t *maskp)
>>  {
>> -	int w, bit = NUMA_NO_NODE;
>> +	int w, bit;
>>  
>>  	w = nodes_weight(*maskp);
>> -	if (w)
>> +	switch (w) {
>> +	case 0:
>> +		bit = NUMA_NO_NODE;
>> +		break;
>> +	case 1:
>> +		bit = __first_node(maskp);
> 
> Per my understanding, first_node() is the formal API and we should use
> that?  Just like we use nodes_weight() instead of __nodes_weight().
> 

updated.

-aneesh