Re: [PATCH 3/5] mm, page_owner: copy page owner info during migration

[Joonsoo Kim]

On Wed, Nov 04, 2015 at 04:00:59PM +0100, Vlastimil Babka wrote:
> The page_owner mechanism stores gfp_flags of an allocation and stack trace
> that lead to it. During page migration, the original information is
> essentially replaced by the allocation of free page as the migration target.
> Arguably this is less useful and might lead to all the page_owner info for
> migratable pages gradually converge towards compaction or numa balancing
> migrations. It has also lead to inaccuracies such as one fixed by commit
> e2cfc91120fa ("mm/page_owner: set correct gfp_mask on page_owner").
> 
> This patch thus introduces copying the page_owner info during migration.
> However, since the fact that the page has been migrated from its original
> place might be useful for debugging, the next patch will introduce a way to
> track that information as well.
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  include/linux/page_owner.h | 10 +++++++++-
>  mm/migrate.c               |  2 ++
>  mm/page_owner.c            | 16 ++++++++++++++++
>  3 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
> index 8e2eb15..6440daa 100644
> --- a/include/linux/page_owner.h
> +++ b/include/linux/page_owner.h
> @@ -11,6 +11,7 @@ extern void __reset_page_owner(struct page *page, unsigned int order);
>  extern void __set_page_owner(struct page *page,
>  			unsigned int order, gfp_t gfp_mask);
>  extern gfp_t __get_page_owner_gfp(struct page *page);
> +extern void __copy_page_owner(struct page *oldpage, struct page *newpage);
>  
>  static inline void reset_page_owner(struct page *page, unsigned int order)
>  {
> @@ -32,6 +33,11 @@ static inline gfp_t get_page_owner_gfp(struct page *page)
>  	else
>  		return 0;
>  }
> +static inline void copy_page_owner(struct page *oldpage, struct page *newpage)
> +{
> +	if (static_branch_unlikely(&page_owner_inited))
> +		__copy_page_owner(oldpage, newpage);
> +}
>  #else
>  static inline void reset_page_owner(struct page *page, unsigned int order)
>  {
> @@ -44,6 +50,8 @@ static inline gfp_t get_page_owner_gfp(struct page *page)
>  {
>  	return 0;
>  }
> -
> +static inline void copy_page_owner(struct page *oldpage, struct page *newpage)
> +{
> +}
>  #endif /* CONFIG_PAGE_OWNER */
>  #endif /* __LINUX_PAGE_OWNER_H */
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 1ae0113..9f82e03 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -38,6 +38,7 @@
>  #include <linux/balloon_compaction.h>
>  #include <linux/mmu_notifier.h>
>  #include <linux/page_idle.h>
> +#include <linux/page_owner.h>
>  
>  #include <asm/tlbflush.h>
>  
> @@ -775,6 +776,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,
>  		set_page_memcg(page, NULL);
>  		if (!PageAnon(page))
>  			page->mapping = NULL;
> +		copy_page_owner(page, newpage);
>  	}
>  	return rc;
>  }
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 7664b85..7ebd3d0 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -84,6 +84,22 @@ gfp_t __get_page_owner_gfp(struct page *page)
>  	return page_ext->gfp_mask;
>  }
>  
> +void __copy_page_owner(struct page *oldpage, struct page *newpage)
> +{
> +	struct page_ext *old_ext = lookup_page_ext(oldpage);
> +	struct page_ext *new_ext = lookup_page_ext(newpage);
> +	int i;
> +
> +	new_ext->order = old_ext->order;
> +	new_ext->gfp_mask = old_ext->gfp_mask;
> +	new_ext->nr_entries = old_ext->nr_entries;
> +
> +	for (i = 0; i < ARRAY_SIZE(new_ext->trace_entries); i++)
> +		new_ext->trace_entries[i] = old_ext->trace_entries[i];
> +
> +	__set_bit(PAGE_EXT_OWNER, &new_ext->flags);
> +}
> +

Need to clear PAGE_EXT_OWNER bit in oldppage.

Thanks.

>  static ssize_t
>  print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		struct page *page, struct page_ext *page_ext)
> -- 
> 2.6.2
> 
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