Re: [PATCH mm-unstable v4 6/6] mm/mempolicy: convert migrate_page_add() to migrate_folio_add()

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

On 1/31/2023 4:18 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>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>

Regards
Yin, Fengwei

> ---
>  mm/mempolicy.c | 39 ++++++++++++++++++++-------------------
>  1 file changed, 20 insertions(+), 19 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 6a68dbce3b70..0919c7a719d4 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;
> @@ -1021,27 +1021,28 @@ 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.
> +	 * We try to migrate only unshared folios. If it is shared it
> +	 * is likely not worth migrating.
> +	 *
> +	 * To check if the folio is shared, ideally we want to make sure
> +	 * every page is mapped to the same process. Doing that is very
> +	 * expensive, so check the estimated mapcount of the folio instead.
>  	 */
> -	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_estimated_sharers(folio) == 1) {
> +		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.
>  			 */
> @@ -1235,7 +1236,7 @@ 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;