linux-kernel - Re: [PATCH 1/3] mm/mempolicy: Use the already fetched local variable

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Date: Mon, 19 Feb 2024 14:04:23 +0530
From: Donet Tom <donettom@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Aneesh Kumar <aneesh.kumar@...nel.org>,
        Huang Ying <ying.huang@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Mel Gorman <mgorman@...e.de>, Ben Widawsky <ben.widawsky@...el.com>,
        Feng Tang <feng.tang@...el.com>, Michal Hocko <mhocko@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>, Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Kravetz
 <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH 1/3] mm/mempolicy: Use the already fetched local variable


On 2/19/24 03:08, Andrew Morton wrote:
> On Sat, 17 Feb 2024 01:31:33 -0600 Donet Tom <donettom@...ux.ibm.com> wrote:
>
>> Avoid doing a per cpu read and use the local variable thisnid. IMHO
>> this also makes the code more readable.
>>
>> ...
>>
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -2526,7 +2526,7 @@ int mpol_misplaced(struct folio *folio, struct vm_area_struct *vma,
>>   		if (node_isset(curnid, pol->nodes))
>>   			goto out;
>>   		z = first_zones_zonelist(
>> -				node_zonelist(numa_node_id(), GFP_HIGHUSER),
>> +				node_zonelist(thisnid, GFP_HIGHUSER),
>>   				gfp_zone(GFP_HIGHUSER),
>>   				&pol->nodes);
>>   		polnid = zone_to_nid(z->zone);
> 	int thisnid = cpu_to_node(thiscpu);
>
> Is there any dofference between numa_node_id() and
> cpu_to_node(raw_smp_processor_id())?  And it it explicable that we're
> using one here and not the other?

Hi Andrew

Both numa_node_id() and cpu_to_node(raw_smp_processor_id()) return the current execution node id,
Since the current execution node is already fetched at the beginning (thisnid) we can reuse it instead of getting it again.

Thanks
Donet Tom

>