linux-kernel - Re: [PATCH v6 20/37] mm: fix non-compound multi-order memory accounting in __free

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Date: Thu, 21 Mar 2024 16:48:53 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Suren Baghdasaryan <surenb@...gle.com>
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Subject: Re: [PATCH v6 20/37] mm: fix non-compound multi-order memory
 accounting in __free_pages

On Thu, Mar 21, 2024 at 09:36:42AM -0700, Suren Baghdasaryan wrote:
>  static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
>  				   unsigned int nr) {}
>  static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}
>  static inline void pgalloc_tag_split(struct page *page, unsigned int nr) {}
> +static inline struct alloc_tag *pgalloc_tag_get(struct page *page) { return NULL; }
> +static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) {}
>  
>  #endif /* CONFIG_MEM_ALLOC_PROFILING */
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fd1cc5b80a56..00e0ae4cbf2d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4700,12 +4700,15 @@ void __free_pages(struct page *page, unsigned int order)
>  {
>  	/* get PageHead before we drop reference */
>  	int head = PageHead(page);
> +	struct alloc_tag *tag = pgalloc_tag_get(page);
>  
>  	if (put_page_testzero(page))
>  		free_the_page(page, order);
> -	else if (!head)
> +	else if (!head) {
> +		pgalloc_tag_sub_pages(tag, (1 << order) - 1);
>  		while (order-- > 0)
>  			free_the_page(page + (1 << order), order);
> +	}

Why do you need these new functions instead of just:

+	else if (!head) {
+		pgalloc_tag_sub(page, (1 << order) - 1);
		while (order-- > 0)
			free_the_page(page + (1 << order), order);
+	}