linux-kernel - Re: [PATCH] ksm: Use a folio inside cmp_and_merge

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Message-ID: <3ee62dcf-c016-4da1-b93e-ca173654a7af@linux.dev>
Date: Wed, 17 Sep 2025 20:21:29 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 akpm@...ux-foundation.org, david@...hat.com, xu.xin16@....com.cn,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Longlong Xia <xialonglong@...inos.cn>
Subject: Re: [PATCH] ksm: Use a folio inside cmp_and_merge_page()

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@...radead.org>

Reviewed-by: Chengming Zhou <chengming.zhou@...ux.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);
>   		}
>   	}
>   }