linux-kernel - Re: [PATCH v2 3/5] mm/memory_hotplug: use nth_page() in place of direct struct page manipulation.

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Message-ID: <6dfbc043-c969-f78d-1e56-5434026246ea@redhat.com>
Date:   Wed, 6 Sep 2023 19:17:02 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>, stable@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v2 3/5] mm/memory_hotplug: use nth_page() in place of
 direct struct page manipulation.

On 06.09.23 17:03, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>

Subject talks about "nth_page()" but that's not what this patch does.

> 
> When dealing with hugetlb pages, manipulating struct page pointers
> directly can get to wrong struct page, since struct page is not guaranteed
> to be contiguous on SPARSEMEM without VMEMMAP. Use nth_page() to handle
> it properly.

^ dito

> 
> Fixes: eeb0efd071d8 ("mm,memory_hotplug: fix scan_movable_pages() for gigantic hugepages")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Muchun Song <songmuchun@...edance.com>
> ---
>   mm/memory_hotplug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1b03f4ec6fd2..3b301c4023ff 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1689,7 +1689,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
>   		 */
>   		if (HPageMigratable(head))
>   			goto found;
> -		skip = compound_nr(head) - (page - head);
> +		skip = compound_nr(head) - (pfn - page_to_pfn(head));
>   		pfn += skip - 1;
>   	}
>   	return -ENOENT;

I suspect systems without VMEMMAP also don't usually support gigantic 
pages AND hotunplug :)

With the subject+description fixed

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb