Re: [PATCH v3 10/14] mm, page_owner: convert page_owner_inited to static key

[Michal Hocko <mhocko@kernel.org>]

On Fri 18-12-15 10:03:22, Vlastimil Babka wrote:
> CONFIG_PAGE_OWNER attempts to impose negligible runtime overhead when enabled
> during compilation, but not actually enabled during runtime by boot param
> page_owner=on. This overhead can be further reduced using the static key
> mechanism, which this patch does.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Sasha Levin <sasha.levin@oracle.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Michal Hocko <mhocko@suse.cz>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  Documentation/vm/page_owner.txt |  9 +++++----
>  include/linux/page_owner.h      | 22 ++++++++++------------
>  mm/page_owner.c                 |  9 +++++----
>  mm/vmstat.c                     |  2 +-
>  4 files changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/Documentation/vm/page_owner.txt b/Documentation/vm/page_owner.txt
> index 8f3ce9b3aa11..ffff1439076a 100644
> --- a/Documentation/vm/page_owner.txt
> +++ b/Documentation/vm/page_owner.txt
> @@ -28,10 +28,11 @@ with page owner and page owner is disabled in runtime due to no enabling
>  boot option, runtime overhead is marginal. If disabled in runtime, it
>  doesn't require memory to store owner information, so there is no runtime
>  memory overhead. And, page owner inserts just two unlikely branches into
> -the page allocator hotpath and if it returns false then allocation is
> -done like as the kernel without page owner. These two unlikely branches
> -would not affect to allocation performance. Following is the kernel's
> -code size change due to this facility.
> +the page allocator hotpath and if not enabled, then allocation is done
> +like as the kernel without page owner. These two unlikely branches should
> +not affect to allocation performance, especially if the static keys jump
> +label patching functionality is available. Following is the kernel's code
> +size change due to this facility.
>  
>  - Without page owner
>     text    data     bss     dec     hex filename
> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
> index cacaabea8a09..8e2eb153c7b9 100644
> --- a/include/linux/page_owner.h
> +++ b/include/linux/page_owner.h
> @@ -1,8 +1,10 @@
>  #ifndef __LINUX_PAGE_OWNER_H
>  #define __LINUX_PAGE_OWNER_H
>  
> +#include <linux/jump_label.h>
> +
>  #ifdef CONFIG_PAGE_OWNER
> -extern bool page_owner_inited;
> +extern struct static_key_false page_owner_inited;
>  extern struct page_ext_operations page_owner_ops;
>  
>  extern void __reset_page_owner(struct page *page, unsigned int order);
> @@ -12,27 +14,23 @@ extern gfp_t __get_page_owner_gfp(struct page *page);
>  
>  static inline void reset_page_owner(struct page *page, unsigned int order)
>  {
> -	if (likely(!page_owner_inited))
> -		return;
> -
> -	__reset_page_owner(page, order);
> +	if (static_branch_unlikely(&page_owner_inited))
> +		__reset_page_owner(page, order);
>  }
>  
>  static inline void set_page_owner(struct page *page,
>  			unsigned int order, gfp_t gfp_mask)
>  {
> -	if (likely(!page_owner_inited))
> -		return;
> -
> -	__set_page_owner(page, order, gfp_mask);
> +	if (static_branch_unlikely(&page_owner_inited))
> +		__set_page_owner(page, order, gfp_mask);
>  }
>  
>  static inline gfp_t get_page_owner_gfp(struct page *page)
>  {
> -	if (likely(!page_owner_inited))
> +	if (static_branch_unlikely(&page_owner_inited))
> +		return __get_page_owner_gfp(page);
> +	else
>  		return 0;
> -
> -	return __get_page_owner_gfp(page);
>  }
>  #else
>  static inline void reset_page_owner(struct page *page, unsigned int order)
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 5392195fca61..c8ea1361146e 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -5,10 +5,11 @@
>  #include <linux/bootmem.h>
>  #include <linux/stacktrace.h>
>  #include <linux/page_owner.h>
> +#include <linux/jump_label.h>
>  #include "internal.h"
>  
>  static bool page_owner_disabled = true;
> -bool page_owner_inited __read_mostly;
> +DEFINE_STATIC_KEY_FALSE(page_owner_inited);
>  
>  static void init_early_allocated_pages(void);
>  
> @@ -37,7 +38,7 @@ static void init_page_owner(void)
>  	if (page_owner_disabled)
>  		return;
>  
> -	page_owner_inited = true;
> +	static_branch_enable(&page_owner_inited);
>  	init_early_allocated_pages();
>  }
>  
> @@ -147,7 +148,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  	struct page *page;
>  	struct page_ext *page_ext;
>  
> -	if (!page_owner_inited)
> +	if (!static_branch_unlikely(&page_owner_inited))
>  		return -EINVAL;
>  
>  	page = NULL;
> @@ -295,7 +296,7 @@ static int __init pageowner_init(void)
>  {
>  	struct dentry *dentry;
>  
> -	if (!page_owner_inited) {
> +	if (!static_branch_unlikely(&page_owner_inited)) {
>  		pr_info("page_owner is disabled\n");
>  		return 0;
>  	}
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 475d154411f0..649680698afe 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1120,7 +1120,7 @@ static void pagetypeinfo_showmixedcount(struct seq_file *m, pg_data_t *pgdat)
>  #ifdef CONFIG_PAGE_OWNER
>  	int mtype;
>  
> -	if (!page_owner_inited)
> +	if (!static_branch_unlikely(&page_owner_inited))
>  		return;
>  
>  	drain_all_pages(NULL);
> -- 
> 2.6.3

-- 
Michal Hocko
SUSE Labs

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