linux-kernel - Re: [RFC PATCH 10/30] mm: enable page allocation tagging for __get_free_pages and alloc

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Date:   Wed, 31 Aug 2022 11:11:03 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, kent.overstreet@...ux.dev,
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Subject: Re: [RFC PATCH 10/30] mm: enable page allocation tagging for
 __get_free_pages and alloc_pages

On Tue, Aug 30, 2022 at 02:48:59PM -0700, Suren Baghdasaryan wrote:
> Redefine alloc_pages, __get_free_pages to record allocations done by
> these functions. Instrument deallocation hooks to record object freeing.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> +#ifdef CONFIG_PAGE_ALLOC_TAGGING
> +
>  #include <linux/alloc_tag.h>
>  #include <linux/page_ext.h>
>  
> @@ -25,4 +27,37 @@ static inline void pgalloc_tag_dec(struct page *page, unsigned int order)
>  		alloc_tag_sub(get_page_tag_ref(page), PAGE_SIZE << order);
>  }
>  
> +/*
> + * Redefinitions of the common page allocators/destructors
> + */
> +#define pgtag_alloc_pages(gfp, order)					\
> +({									\
> +	struct page *_page = _alloc_pages((gfp), (order));		\
> +									\
> +	if (_page)							\
> +		alloc_tag_add(get_page_tag_ref(_page), PAGE_SIZE << (order));\
> +	_page;								\
> +})
> +

Instead of renaming alloc_pages, why is the tagging not done in
__alloc_pages()? At least __alloc_pages_bulk() is also missed. The branch
can be guarded with IS_ENABLED.

> +#define pgtag_get_free_pages(gfp_mask, order)				\
> +({									\
> +	struct page *_page;						\
> +	unsigned long _res = _get_free_pages((gfp_mask), (order), &_page);\
> +									\
> +	if (_res)							\
> +		alloc_tag_add(get_page_tag_ref(_page), PAGE_SIZE << (order));\
> +	_res;								\
> +})
> +

Similar, the tagging could happen in a core function instead of a wrapper.

> +#else /* CONFIG_PAGE_ALLOC_TAGGING */
> +
> +#define pgtag_alloc_pages(gfp, order) _alloc_pages(gfp, order)
> +
> +#define pgtag_get_free_pages(gfp_mask, order) \
> +	_get_free_pages((gfp_mask), (order), NULL)
> +
> +#define pgalloc_tag_dec(__page, __size)		do {} while (0)
> +
> +#endif /* CONFIG_PAGE_ALLOC_TAGGING */
> +
>  #endif /* _LINUX_PGALLOC_TAG_H */
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index b73d3248d976..f7e6d9564a49 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2249,7 +2249,7 @@ EXPORT_SYMBOL(vma_alloc_folio);
>   * flags are used.
>   * Return: The page on success or NULL if allocation fails.
>   */
> -struct page *alloc_pages(gfp_t gfp, unsigned order)
> +struct page *_alloc_pages(gfp_t gfp, unsigned int order)
>  {
>  	struct mempolicy *pol = &default_policy;
>  	struct page *page;
> @@ -2273,7 +2273,7 @@ struct page *alloc_pages(gfp_t gfp, unsigned order)
>  
>  	return page;
>  }
> -EXPORT_SYMBOL(alloc_pages);
> +EXPORT_SYMBOL(_alloc_pages);
>  
>  struct folio *folio_alloc(gfp_t gfp, unsigned order)
>  {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e5486d47406e..165daba19e2a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -763,6 +763,7 @@ static inline bool pcp_allowed_order(unsigned int order)
>  
>  static inline void free_the_page(struct page *page, unsigned int order)
>  {
> +
>  	if (pcp_allowed_order(order))		/* Via pcp? */
>  		free_unref_page(page, order);
>  	else

Spurious wide-space change.

-- 
Mel Gorman
SUSE Labs