linux-kernel - Re: [PATCH v3 11/26] x86/numa: use get_pfn_range_for

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Message-ID: <66b1302ce5fd3_c1448294d3@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 5 Aug 2024 13:03:56 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Mike Rapoport <rppt@...nel.org>, <linux-kernel@...r.kernel.org>
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Subject: Re: [PATCH v3 11/26] x86/numa: use get_pfn_range_for_nid to verify
 that node spans memory

Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> Instead of looping over numa_meminfo array to detect node's start and
> end addresses use get_pfn_range_for_init().
> 
> This is shorter and make it easier to lift numa_memblks to generic code.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> Tested-by: Zi Yan <ziy@...dia.com> # for x86_64 and arm64
> ---
>  arch/x86/mm/numa.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index edfc38803779..cfe7e5477cf8 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -521,17 +521,10 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
>  
>  	/* Finally register nodes. */
>  	for_each_node_mask(nid, node_possible_map) {
> -		u64 start = PFN_PHYS(max_pfn);
> -		u64 end = 0;
> +		unsigned long start_pfn, end_pfn;
>  
> -		for (i = 0; i < mi->nr_blks; i++) {
> -			if (nid != mi->blk[i].nid)
> -				continue;
> -			start = min(mi->blk[i].start, start);
> -			end = max(mi->blk[i].end, end);
> -		}
> -
> -		if (start >= end)
> +		get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
> +		if (start_pfn >= end_pfn)

Assuming I understand why this works, would it be worth a comment like:

"Note, get_pfn_range_for_nid() depends on memblock_set_node() having
 already happened"

...at least that context was not part of the diff so took me second to
figure out how this works.