[PATCH 1/1] mm/ksm: remove page_stable_node() and use folio_stable_node() directly

[PATCH 1/1] mm/ksm: remove page_stable_node() and use folio_stable_node() directly

[Longlong Xia]

The page_stable_node() function was a trivial wrapper around
folio_stable_node() that had only one call site. Remove this
unnecessary helper and call folio_stable_node(page_folio(page))
directly at that site.There is no functional change.

Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
---
 mm/ksm.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 160787bb121c..eab5348d19a7 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1061,11 +1061,6 @@ struct ksm_stable_node *folio_stable_node(const struct folio *folio)
 	return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
 }
 
-static inline struct ksm_stable_node *page_stable_node(struct page *page)
-{
-	return folio_stable_node(page_folio(page));
-}
-
 static inline void folio_set_stable_node(struct folio *folio,
 					 struct ksm_stable_node *stable_node)
 {
@@ -2233,7 +2228,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 	int err;
 	bool max_page_sharing_bypass = false;
 
-	stable_node = page_stable_node(page);
+	stable_node = folio_stable_node(page_folio(page));
 	if (stable_node) {
 		if (stable_node->head != &migrate_nodes &&
 		    get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
-- 
2.43.0

[PATCH] ksm: Use a folio inside cmp_and_merge_page()

[Matthew Wilcox (Oracle)]

This removes the last call to page_stable_node(), so delete the
wrapper.  It also removes a call to trylock_page() and saves a call to
compound_head(), as well as removing a reference to folio->page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/ksm.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 8583fb91ef13..47655ca8f9a5 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1057,11 +1057,6 @@ struct ksm_stable_node *folio_stable_node(const struct folio *folio)
 	return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
 }
 
-static inline struct ksm_stable_node *page_stable_node(struct page *page)
-{
-	return folio_stable_node(page_folio(page));
-}
-
 static inline void folio_set_stable_node(struct folio *folio,
 					 struct ksm_stable_node *stable_node)
 {
@@ -2221,6 +2216,7 @@ static void stable_tree_append(struct ksm_rmap_item *rmap_item,
  */
 static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item)
 {
+	struct folio *folio = page_folio(page);
 	struct ksm_rmap_item *tree_rmap_item;
 	struct page *tree_page = NULL;
 	struct ksm_stable_node *stable_node;
@@ -2229,7 +2225,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 	int err;
 	bool max_page_sharing_bypass = false;
 
-	stable_node = page_stable_node(page);
+	stable_node = folio_stable_node(folio);
 	if (stable_node) {
 		if (stable_node->head != &migrate_nodes &&
 		    get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
@@ -2268,7 +2264,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 
 	/* Start by searching for the folio in the stable tree */
 	kfolio = stable_tree_search(page);
-	if (&kfolio->page == page && rmap_item->head == stable_node) {
+	if (kfolio == folio && rmap_item->head == stable_node) {
 		folio_put(kfolio);
 		return;
 	}
@@ -2349,10 +2345,11 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 			 * the page is locked, it is better to skip it and
 			 * perhaps try again later.
 			 */
-			if (!trylock_page(page))
+			if (!folio_trylock(folio))
 				return;
 			split_huge_page(page);
-			unlock_page(page);
+			folio = page_folio(page);
+			folio_unlock(folio);
 		}
 	}
 }
-- 
2.47.2

Re: [PATCH] ksm: Use a folio inside cmp_and_merge_page()

[David Hildenbrand]

On 16.09.25 20:11, Matthew Wilcox (Oracle) wrote:
> This removes the last call to page_stable_node(), so delete the
> wrapper.  It also removes a call to trylock_page() and saves a call to
> compound_head(), as well as removing a reference to folio->page.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb

Re: [PATCH] ksm: Use a folio inside cmp_and_merge_page()

[Chengming Zhou]

On 2025/9/17 02:11, Matthew Wilcox (Oracle) wrote:
> This removes the last call to page_stable_node(), so delete the
> wrapper.  It also removes a call to trylock_page() and saves a call to
> compound_head(), as well as removing a reference to folio->page.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>

Thanks.

> ---
>   mm/ksm.c | 15 ++++++---------
>   1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 8583fb91ef13..47655ca8f9a5 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1057,11 +1057,6 @@ struct ksm_stable_node *folio_stable_node(const struct folio *folio)
>   	return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
>   }
>   
> -static inline struct ksm_stable_node *page_stable_node(struct page *page)
> -{
> -	return folio_stable_node(page_folio(page));
> -}
> -
>   static inline void folio_set_stable_node(struct folio *folio,
>   					 struct ksm_stable_node *stable_node)
>   {
> @@ -2221,6 +2216,7 @@ static void stable_tree_append(struct ksm_rmap_item *rmap_item,
>    */
>   static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item)
>   {
> +	struct folio *folio = page_folio(page);
>   	struct ksm_rmap_item *tree_rmap_item;
>   	struct page *tree_page = NULL;
>   	struct ksm_stable_node *stable_node;
> @@ -2229,7 +2225,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
>   	int err;
>   	bool max_page_sharing_bypass = false;
>   
> -	stable_node = page_stable_node(page);
> +	stable_node = folio_stable_node(folio);
>   	if (stable_node) {
>   		if (stable_node->head != &migrate_nodes &&
>   		    get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
> @@ -2268,7 +2264,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
>   
>   	/* Start by searching for the folio in the stable tree */
>   	kfolio = stable_tree_search(page);
> -	if (&kfolio->page == page && rmap_item->head == stable_node) {
> +	if (kfolio == folio && rmap_item->head == stable_node) {
>   		folio_put(kfolio);
>   		return;
>   	}
> @@ -2349,10 +2345,11 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
>   			 * the page is locked, it is better to skip it and
>   			 * perhaps try again later.
>   			 */
> -			if (!trylock_page(page))
> +			if (!folio_trylock(folio))
>   				return;
>   			split_huge_page(page);
> -			unlock_page(page);
> +			folio = page_folio(page);
> +			folio_unlock(folio);
>   		}
>   	}
>   }

Re: [PATCH 1/1] mm/ksm: remove page_stable_node() and use folio_stable_node() directly

[Matthew Wilcox]

On Tue, Sep 16, 2025 at 04:05:33PM +0800, Longlong Xia wrote:
> The page_stable_node() function was a trivial wrapper around
> folio_stable_node() that had only one call site. Remove this
> unnecessary helper and call folio_stable_node(page_folio(page))
> directly at that site.There is no functional change.

I just sent a replacement for this patch as a reply.  I've been sitting
on it since last December as it didn't really feel important nough to
send, but if people are going to try to do this kind of thing, may as
well do it properly.