On Mon, Dec 10, 2018 at 02:35:13PM -0800, Anthony Yznaga wrote:
> Certain pages that are never mapped to userspace have a type
> indicated in the page_type field of their struct pages (e.g. PG_buddy).
> page_type overlaps with _mapcount so set the count to 0 and avoid
> calling page_mapcount() for these pages.
>
> Signed-off-by: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx>
> Acked-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Looks good to me.
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> ---
> v2 - incorporated feedback from Matthew Wilcox
>
> fs/proc/page.c | 2 +-
> include/linux/page-flags.h | 6 ++++++
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 6c517b11acf8..40b05e0d4274 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -46,7 +46,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
> ppage = pfn_to_page(pfn);
> else
> ppage = NULL;
> - if (!ppage || PageSlab(ppage))
> + if (!ppage || PageSlab(ppage) || page_has_type(ppage))
> pcount = 0;
> else
> pcount = page_mapcount(ppage);
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 50ce1bddaf56..39b4494e29f1 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -669,6 +669,7 @@ static inline int TestClearPageDoubleMap(struct page *page)
>
> #define PAGE_TYPE_BASE 0xf0000000
> /* Reserve 0x0000007f to catch underflows of page_mapcount */
> +#define PAGE_MAPCOUNT_RESERVE -128
> #define PG_buddy 0x00000080
> #define PG_balloon 0x00000100
> #define PG_kmemcg 0x00000200
> @@ -677,6 +678,11 @@ static inline int TestClearPageDoubleMap(struct page *page)
> #define PageType(page, flag) \
> ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
>
> +static inline int page_has_type(struct page *page)
> +{
> + return (int)page->page_type < PAGE_MAPCOUNT_RESERVE;
> +}
> +
> #define PAGE_TYPE_OPS(uname, lname) \
> static __always_inline int Page##uname(struct page *page) \
> { \
> --
> 1.8.3.1
>
>
