Re: [PATCH v2 2/2] mm/damon/ops-common: factor out damon_putback_folio_list()

[SJ Park]

'get_maintainer.pl --nogit --nogit-fallback' suggests adding below recipients.
I added them.  Please consier using get_maintainer.pl from the next time.

- linux-mm@xxxxxxxxx
- linux-kernel@xxxxxxxxxxxxxxx

On Fri, 24 Jul 2026 14:01:35 +0800 dayou5941@xxxxxxx wrote:

> From: liyouhong <liyouhong@xxxxxxxxxx>
> 
> The putback loop is duplicated in damon_migrate_folio_list() and on the
> invalid-nid path of damon_migrate_pages().  Factor it into a small helper
> for readability.  No functional change.

This is not a hotfix.  I'd suggest sending this separately, not together with
the first patch of this series.  Sending hotfix together with non-hotfix when
they don't really need to be applied together only makes it complicated.

> 
> Signed-off-by: liyouhong <liyouhong@xxxxxxxxxx>
> ---
>  mm/damon/ops-common.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> index f5ded45fabd1..9a1e8aec5444 100644
> --- a/mm/damon/ops-common.c
> +++ b/mm/damon/ops-common.c
> @@ -331,12 +331,22 @@ static unsigned int __damon_migrate_folio_list(
>  	return nr_succeeded;
>  }
>  
> +static void damon_putback_folio_list(struct list_head *folio_list)
> +{
> +	struct folio *folio;
> +
> +	while (!list_empty(folio_list)) {
> +		folio = lru_to_folio(folio_list);
> +		list_del(&folio->lru);
> +		folio_putback_lru(folio);
> +	}
> +}
> +
>  static unsigned int damon_migrate_folio_list(struct list_head *folio_list,
>  						struct pglist_data *pgdat,
>  						int target_nid)
>  {
>  	unsigned int nr_migrated = 0;
> -	struct folio *folio;
>  	LIST_HEAD(ret_folios);
>  	LIST_HEAD(migrate_folios);
>  
> @@ -374,11 +384,7 @@ static unsigned int damon_migrate_folio_list(struct list_head *folio_list,
>  
>  	list_splice(&ret_folios, folio_list);
>  
> -	while (!list_empty(folio_list)) {
> -		folio = lru_to_folio(folio_list);
> -		list_del(&folio->lru);
> -		folio_putback_lru(folio);
> -	}
> +	damon_putback_folio_list(folio_list);
>  
>  	return nr_migrated;
>  }
> @@ -395,12 +401,7 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
>  
>  	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
>  			!node_state(target_nid, N_MEMORY)) {
> -		while (!list_empty(folio_list)) {
> -			struct folio *folio = lru_to_folio(folio_list);
> -
> -			list_del(&folio->lru);
> -			folio_putback_lru(folio);
> -		}
> +		damon_putback_folio_list(folio_list);
>  		return nr_migrated;
>  	}

Looks better.  But, how about further simplifying it by moving the folios
putback from damon_migrate_pages(), and doing that from damon_migrate_pages()?
damon_migrate_pages() would do the putback always before returning, and the
taregt_nid path will 'goto' the path.  E.g.,

--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -391,15 +391,8 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
                return nr_migrated;

        if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
-                       !node_state(target_nid, N_MEMORY)) {
-               while (!list_empty(folio_list)) {
-                       struct folio *folio = lru_to_folio(folio_list);
-
-                       list_del(&folio->lru);
-                       folio_putback_lru(folio);
-               }
-               return nr_migrated;
-       }
+                       !node_state(target_nid, N_MEMORY))
+               goto out;

        noreclaim_flag = memalloc_noreclaim_save();

@@ -424,6 +417,14 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)

        memalloc_noreclaim_restore(noreclaim_flag);

+out:
+
+       while (!list_empty(folio_list)) {
+               struct folio *folio = lru_to_folio(folio_list);
+
+               list_del(&folio->lru);
+               folio_putback_lru(folio);
+       }
        return nr_migrated;
 }

This could be applied to the first patch.  And this patch can simply remove the
redundanty putback.

>  
> -- 
> 2.25.1

[1] https://lore.kernel.org/20260724060707.CE1F81F000E9@xxxxxxxxxxxxxxx


Thanks,
SJ