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

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Date: Sun, 18 Feb 2024 13:38:51 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Donet Tom <donettom@...ux.ibm.com>
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 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?