Re: [PATCH v3 11/14] mm, page_owner: copy page owner info during migration

[Michal Hocko]

On Fri 18-12-15 10:03:23, 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
> practically 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>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  include/linux/page_owner.h | 10 +++++++++-
>  mm/migrate.c               |  3 +++
>  mm/page_owner.c            | 25 +++++++++++++++++++++++++
>  3 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
> index 8e2eb153c7b9..6440daab4ef8 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 b1034f9c77e7..863a0f1fe23f 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>
>  
> @@ -578,6 +579,8 @@ void migrate_page_copy(struct page *newpage, struct page *page)
>  	 */
>  	if (PageWriteback(newpage))
>  		end_page_writeback(newpage);
> +
> +	copy_page_owner(page, newpage);
>  }
>  
>  /************************************************************
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index c8ea1361146e..a390d2665df2 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -84,6 +84,31 @@ 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];
> +
> +	/*
> +	 * We don't clear the bit on the oldpage as it's going to be freed
> +	 * after migration. Until then, the info can be useful in case of
> +	 * a bug, and the overal stats will be off a bit only temporarily.
> +	 * Also, migrate_misplaced_transhuge_page() can still fail the
> +	 * migration and then we want the oldpage to retain the info. But
> +	 * in that case we also don't need to explicitly clear the info from
> +	 * the new page, which will be freed.
> +	 */
> +	__set_bit(PAGE_EXT_OWNER, &new_ext->flags);
> +}
> +
>  static ssize_t
>  print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  		struct page *page, struct page_ext *page_ext)
> -- 
> 2.6.3

-- 
Michal Hocko
SUSE Labs
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