Re: [PATCH -next v2 1/2] mm: compaction: convert to use a folio in isolate_migratepages_block()

[Baolin Wang]

Hi

On 6/19/2023 7:07 PM, Kefeng Wang wrote:
> Directly use a folio instead of page_folio() when page successfully
> isolated (hugepage and movable page) and after folio_get_nontail_page(),
> which removes several calls to compound_head().
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
> v2:
> - update comments and use node_stat_mod_folio, per Matthew Wilcox
> - add missed PageLRU conversion and rebase on next-20230619
>
>   mm/compaction.c | 84 ++++++++++++++++++++++++++-----------------------
>   1 file changed, 44 insertions(+), 40 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 6149a2d324be..0334eefe4bfa 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -795,6 +795,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>   	struct lruvec *lruvec;
>   	unsigned long flags = 0;
>   	struct lruvec *locked = NULL;
> +	struct folio *folio = NULL;
>   	struct page *page = NULL, *valid_page = NULL;
>   	struct address_space *mapping;
>   	unsigned long start_pfn = low_pfn;
> @@ -891,7 +892,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>   		if (!valid_page && pageblock_aligned(low_pfn)) {
>   			if (!isolation_suitable(cc, page)) {
>   				low_pfn = end_pfn;
> -				page = NULL;
> +				folio = NULL;
>   				goto isolate_abort;
>   			}
>   			valid_page = page;
> @@ -923,7 +924,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>   				 * Hugepage was successfully isolated and placed
>   				 * on the cc->migratepages list.
>   				 */
> -				low_pfn += compound_nr(page) - 1;
> +				folio = page_folio(page);
> +				low_pfn += folio_nr_pages(folio) - 1;
>   				goto isolate_success_no_list;
>   			}
>   
> @@ -991,8 +993,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>   					locked = NULL;
>   				}
>   
> -				if (isolate_movable_page(page, mode))
> +				if (isolate_movable_page(page, mode)) {
> +					folio = page_folio(page);
>   					goto isolate_success;
> +				}
>   			}
>   
>   			goto isolate_fail;
> @@ -1003,7 +1007,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>   		 * sure the page is not being freed elsewhere -- the
>   		 * page release code relies on it.
>   		 */
> -		if (unlikely(!get_page_unless_zero(page)))
> +		folio = folio_get_nontail_page(page);

I'm just curious, how can you make sure the 'page' is not a tail page? 
Since the validation is lockless.