Re: [PATCH v2 5/5] mm: memory_hotplug: unify Huge/LRU/non-LRU movable folio isolation

[Miaohe Lin <linmiaohe@huawei.com>]

On 2024/8/17 16:49, Kefeng Wang wrote:
> Use the isolate_folio_to_list() to unify hugetlb/LRU/non-LRU
> folio isolation, which cleanup code a bit and save a few calls
> to compound_head().
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  mm/memory_hotplug.c | 45 +++++++++++++++++----------------------------
>  1 file changed, 17 insertions(+), 28 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 02a0d4fbc3fe..cc9c16db2f8c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1773,14 +1773,14 @@ 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;
>  	LIST_HEAD(source);
> +	struct folio *folio;
>  	static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL,
>  				      DEFAULT_RATELIMIT_BURST);
>  
>  	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> -		struct folio *folio;
> -		bool isolated;
> +		struct page *page;
> +		bool huge;
>  
>  		if (!pfn_valid(pfn))
>  			continue;
> @@ -1812,34 +1812,22 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>  			continue;
>  		}
>  
> -		if (folio_test_hugetlb(folio)) {
> -			isolate_hugetlb(folio, &source);
> -			continue;
> +		huge = folio_test_hugetlb(folio);
> +		if (!huge) {
> +			folio = folio_get_nontail_page(page);
> +			if (!folio)
> +				continue;
>  		}
>  
> -		if (!get_page_unless_zero(page))

Does page always equal to head? Page is used in most cases in this function and head is only used to calculate pfn.
If not, folio can not simply replace page?

> -			continue;
> -		/*
> -		 * We can skip free pages. And we can deal with pages on
> -		 * LRU and non-lru movable pages.
> -		 */
> -		if (PageLRU(page))

I think this check is incorrect. We should check __PageMovable(page) instead. So this patch
fixes this issue too.

Thanks.
.