Re: [PATCH 4/6] mm: migrate_device: use more folio in migrate_device_finalize()

[Alistair Popple <apopple@nvidia.com>]

Kefeng Wang <wangkefeng.wang@huawei.com> writes:

> Saves a couple of calls to compound_head() and remove last two callers
> of putback_lru_page().
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  mm/migrate_device.c | 41 ++++++++++++++++++++++-------------------
>  1 file changed, 22 insertions(+), 19 deletions(-)
>
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index b49f4956617a..6ea3d055f520 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -815,42 +815,45 @@ void migrate_device_finalize(unsigned long *src_pfns,
>  	unsigned long i;
>  
>  	for (i = 0; i < npages; i++) {
> -		struct folio *dst, *src;
> +		struct folio *dst = NULL, *src = NULL;
>  		struct page *newpage = migrate_pfn_to_page(dst_pfns[i]);
>  		struct page *page = migrate_pfn_to_page(src_pfns[i]);

We could probably simplify this even further with a
migrate_pfn_to_folio() function. I'm still working on extending
ZONE_DEVICE to support higher order folios though (held up fixing
refcounts) so this can wait until then.

Reviewed-by: Alistair Popple <apopple@nvidia.com>

>  
> +		if (newpage)
> +			dst = page_folio(newpage);
> +
>  		if (!page) {
> -			if (newpage) {
> -				unlock_page(newpage);
> -				put_page(newpage);
> +			if (dst) {
> +				folio_unlock(dst);
> +				folio_put(dst);
>  			}
>  			continue;
>  		}
>  
> -		if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
> -			if (newpage) {
> -				unlock_page(newpage);
> -				put_page(newpage);
> +		src = page_folio(page);
> +
> +		if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE) || !dst) {
> +			if (dst) {
> +				folio_unlock(dst);
> +				folio_put(dst);
>  			}
> -			newpage = page;
> +			dst = src;
>  		}
>  
> -		src = page_folio(page);
> -		dst = page_folio(newpage);
>  		remove_migration_ptes(src, dst, false);
>  		folio_unlock(src);
>  
> -		if (is_zone_device_page(page))
> -			put_page(page);
> +		if (folio_is_zone_device(src))
> +			folio_put(src);
>  		else
> -			putback_lru_page(page);
> +			folio_putback_lru(src);
>  
> -		if (newpage != page) {
> -			unlock_page(newpage);
> -			if (is_zone_device_page(newpage))
> -				put_page(newpage);
> +		if (dst != src) {
> +			folio_unlock(dst);
> +			if (folio_is_zone_device(dst))
> +				folio_put(dst);
>  			else
> -				putback_lru_page(newpage);
> +				folio_putback_lru(dst);
>  		}
>  	}
>  }