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@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>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> 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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