Re: [PATCH v2 1/5] mm: memory_hotplug: remove head variable in do_migrate_range()

[David Hildenbrand <david@redhat.com>]

On 17.08.24 10:49, Kefeng Wang wrote:
> Directly use a folio for HugeTLB and THP when calculate the next pfn,
> then remove unused head variable.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>   mm/memory_hotplug.c | 22 ++++++++++++++--------
>   1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index df291f2e509d..dc19b0e28fbc 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1773,7 +1773,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
>   static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   {
>   	unsigned long pfn;
> -	struct page *page, *head;
> +	struct page *page;
>   	LIST_HEAD(source);
>   	static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL,
>   				      DEFAULT_RATELIMIT_BURST);
> @@ -1786,14 +1786,20 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>   			continue;
>   		page = pfn_to_page(pfn);
>   		folio = page_folio(page);
> -		head = &folio->page;
>   
> -		if (PageHuge(page)) {
> -			pfn = page_to_pfn(head) + compound_nr(head) - 1;
> -			isolate_hugetlb(folio, &source);
> -			continue;
> -		} else if (PageTransHuge(page))
> -			pfn = page_to_pfn(head) + thp_nr_pages(page) - 1;
> +		/*
> +		 * The folio hold no reference or lock, it might be changed
> +		 * concurrently(eg, split), folio_nr_pages() may read garbage,
> +		 * but out loop could handle that as it revisits the split
> +		 * folio later.
> +		 */
> +		if (folio_test_large(folio)) {
> +			pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1;
> +			if (folio_test_hugetlb(folio)) {
> +				isolate_hugetlb(folio, &source);
> +				continue;
> +			}
> +		}
>   
>   		/*
>   		 * HWPoison pages have elevated reference counts so the migration would

With the comment cleanup

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

-- 
Cheers,

David / dhildenb