Re: [PATCH v4 4/7] mm: page_owner: add support for splitting to any order in split page_owner.

[David Hildenbrand <david@xxxxxxxxxx>]

On 13.02.24 22:55, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> It adds a new_order parameter to set new page order in page owner.
> It prepares for upcoming changes to support split huge page to any
> lower order.
>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
>   include/linux/page_owner.h | 10 +++++-----
>   mm/huge_memory.c           |  2 +-
>   mm/page_alloc.c            |  4 ++--
>   mm/page_owner.c            |  9 +++++----
>   4 files changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
> index d7878523adfc..a784ba69f67f 100644
> --- a/include/linux/page_owner.h
> +++ b/include/linux/page_owner.h
> @@ -11,7 +11,7 @@ extern struct page_ext_operations page_owner_ops;
>   extern void __reset_page_owner(struct page *page, unsigned short order);
>   extern void __set_page_owner(struct page *page,
>   			unsigned short order, gfp_t gfp_mask);
> -extern void __split_page_owner(struct page *page, int order);
> +extern void __split_page_owner(struct page *page, int old_order, int new_order);
>   extern void __folio_copy_owner(struct folio *newfolio, struct folio *old);
>   extern void __set_page_owner_migrate_reason(struct page *page, int reason);
>   extern void __dump_page_owner(const struct page *page);
> @@ -31,10 +31,10 @@ static inline void set_page_owner(struct page *page,
>   		__set_page_owner(page, order, gfp_mask);
>   }
>   
> -static inline void split_page_owner(struct page *page, int order)
> +static inline void split_page_owner(struct page *page, int old_order, int new_order)
>   {
>   	if (static_branch_unlikely(&page_owner_inited))
> -		__split_page_owner(page, order);
> +		__split_page_owner(page, old_order, new_order);
>   }
>   static inline void folio_copy_owner(struct folio *newfolio, struct folio *old)
>   {
> @@ -56,11 +56,11 @@ static inline void reset_page_owner(struct page *page, unsigned short order)
>   {
>   }
>   static inline void set_page_owner(struct page *page,
> -			unsigned int order, gfp_t gfp_mask)
> +			unsigned short order, gfp_t gfp_mask)
>   {
>   }
>   static inline void split_page_owner(struct page *page,
> -			int order)
> +			int old_order, int new_order)
>   {
>   }
>   static inline void folio_copy_owner(struct folio *newfolio, struct folio *folio)
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 3d30eccd3a7f..ad7133c97428 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2919,7 +2919,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>   	unlock_page_lruvec(lruvec);
>   	/* Caller disabled irqs, so they are still disabled here */
>   
> -	split_page_owner(head, order);
> +	split_page_owner(head, order, 0);
>   
>   	/* See comment in __split_huge_page_tail() */
>   	if (PageAnon(head)) {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9d4dd41d0647..e0f107b21c98 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2652,7 +2652,7 @@ void split_page(struct page *page, unsigned int order)
>   
>   	for (i = 1; i < (1 << order); i++)
>   		set_page_refcounted(page + i);
> -	split_page_owner(page, order);
> +	split_page_owner(page, order, 0);
>   	split_page_memcg(page, order, 0);
>   }
>   EXPORT_SYMBOL_GPL(split_page);
> @@ -4837,7 +4837,7 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
>   		struct page *page = virt_to_page((void *)addr);
>   		struct page *last = page + nr;
>   
> -		split_page_owner(page, order);
> +		split_page_owner(page, order, 0);
>   		split_page_memcg(page, order, 0);
>   		while (page < --last)
>   			set_page_refcounted(last);
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 1319e402c2cf..ebbffa0501db 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -292,19 +292,20 @@ void __set_page_owner_migrate_reason(struct page *page, int reason)
>   	page_ext_put(page_ext);
>   }
>   
> -void __split_page_owner(struct page *page, int order)
> +void __split_page_owner(struct page *page, int old_order, int new_order)
>   {
>   	int i;
>   	struct page_ext *page_ext = page_ext_get(page);
>   	struct page_owner *page_owner;
> -	unsigned int nr = 1 << order;
> +	unsigned int old_nr = 1 << old_order;
> +	unsigned int new_nr = 1 << new_order;
>   
>   	if (unlikely(!page_ext))
>   		return;
>   
> -	for (i = 0; i < nr; i++) {
> +	for (i = 0; i < old_nr; i += new_nr) {
>   		page_owner = get_page_owner(page_ext);
> -		page_owner->order = 0;
> +		page_owner->order = new_order;
>   		page_ext = page_ext_next(page_ext);

Staring at __set_page_owner_handle(), we do set all 1<<order page_exts 
(corresponding to 1<<order "struct page"s) to have ->order set.

Wouldn't you have to do the same here?

for (i = 0; i < 1 << old_order; i++) {
	page_owner = get_page_owner(page_ext);
	page_owner->order = new_order;
	page_ext = page_ext_next(page_ext);
}

--
Cheers,

David / dhildenb