Re: [PATCH mm-unstable 5/5] mm/mempolicy: Convert migrate_page_add() to migrate_folio_add()

["Yin, Fengwei" <fengwei.yin@intel.com>]

On 1/19/2023 7:22 AM, Vishal Moola (Oracle) wrote:
> Replace migrate_page_add() with migrate_folio_add().
> migrate_folio_add() does the same a migrate_page_add() but takes in a
> folio instead of a page. This removes a couple of calls to
> compound_head().
> 
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
> ---
>  mm/mempolicy.c | 34 +++++++++++++++-------------------
>  1 file changed, 15 insertions(+), 19 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 0a3690ecab7d..253ce368cf16 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -414,7 +414,7 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
>  	},
>  };
>  
> -static int migrate_page_add(struct page *page, struct list_head *pagelist,
> +static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
>  				unsigned long flags);
>  
>  struct queue_pages {
> @@ -476,7 +476,7 @@ static int queue_folios_pmd(pmd_t *pmd, spinlock_t *ptl, unsigned long addr,
>  	/* go to folio migration */
>  	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
>  		if (!vma_migratable(walk->vma) ||
> -		    migrate_page_add(&folio->page, qp->pagelist, flags)) {
> +		    migrate_folio_add(folio, qp->pagelist, flags)) {
>  			ret = 1;
>  			goto unlock;
>  		}
> @@ -544,7 +544,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
>  			 * temporary off LRU pages in the range.  Still
>  			 * need migrate other LRU pages.
>  			 */
> -			if (migrate_page_add(&folio->page, qp->pagelist, flags))
> +			if (migrate_folio_add(folio, qp->pagelist, flags))
>  				has_unmovable = true;
>  		} else
>  			break;
> @@ -1022,27 +1022,23 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
>  }
>  
>  #ifdef CONFIG_MIGRATION
> -/*
> - * page migration, thp tail pages can be passed.
> - */
> -static int migrate_page_add(struct page *page, struct list_head *pagelist,
> +static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
>  				unsigned long flags)
>  {
> -	struct page *head = compound_head(page);
>  	/*
> -	 * Avoid migrating a page that is shared with others.
> +	 * Avoid migrating a folio that is shared with others.
>  	 */
> -	if ((flags & MPOL_MF_MOVE_ALL) || page_mapcount(head) == 1) {
> -		if (!isolate_lru_page(head)) {
> -			list_add_tail(&head->lru, pagelist);
> -			mod_node_page_state(page_pgdat(head),
> -				NR_ISOLATED_ANON + page_is_file_lru(head),
> -				thp_nr_pages(head));
> +	if ((flags & MPOL_MF_MOVE_ALL) || folio_mapcount(folio) == 1) {
One question to the page_mapcount -> folio_mapcount here.

For a large folio with 0 entire mapcount, if the first sub-page and any
other sub-page are mapped, page_mapcount(head) == 1 is true while
folio_mapcount(folio) == 1 is not.

Regards
Yin, Fengwei

> +		if (!folio_isolate_lru(folio)) {
> +			list_add_tail(&folio->lru, foliolist);
> +			node_stat_mod_folio(folio,
> +				NR_ISOLATED_ANON + folio_is_file_lru(folio),
> +				folio_nr_pages(folio));
>  		} else if (flags & MPOL_MF_STRICT) {
>  			/*
> -			 * Non-movable page may reach here.  And, there may be
> -			 * temporary off LRU pages or non-LRU movable pages.
> -			 * Treat them as unmovable pages since they can't be
> +			 * Non-movable folio may reach here.  And, there may be
> +			 * temporary off LRU folios or non-LRU movable folios.
> +			 * Treat them as unmovable folios since they can't be
>  			 * isolated, so they can't be moved at the moment.  It
>  			 * should return -EIO for this case too.
>  			 */
> @@ -1234,7 +1230,7 @@ static struct page *new_page(struct page *page, unsigned long start)
>  }
>  #else
>  
> -static int migrate_page_add(struct page *page, struct list_head *pagelist,
> +static int migrate_folio_add(struct folio *folio, struct list_head *foliolist,
>  				unsigned long flags)
>  {
>  	return -EIO;