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

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Date: Mon, 19 Feb 2024 17:21:30 -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 Mon, 19 Feb 2024 14:04:23 +0530 Donet Tom <donettom@...ux.ibm.com> wrote:

> >> --- 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.

Sure, but mine was a broader thought: why do we have both?  Is one
preferable and if so why?