On Tue, Dec 04, 2018 at 02:45:26PM -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>
> ---
> fs/proc/page.c | 2 +-
> include/linux/page-flags.h | 7 +++++++
> 2 files changed, 8 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..f9a1c50ccefc 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -673,10 +673,17 @@ static inline int TestClearPageDoubleMap(struct page *page)
> #define PG_balloon 0x00000100
> #define PG_kmemcg 0x00000200
> #define PG_table 0x00000400
> +#define PAGE_TYPE_ALL (PG_buddy | PG_balloon | PG_kmemcg | PG_table)
>
> #define PageType(page, flag) \
> ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
>
> +static inline int page_has_type(struct page *page)
> +{
> + return (PageType(page, 0) &&
> + ((page->page_type & PAGE_TYPE_ALL) != PAGE_TYPE_ALL));
> +}
> +
> #define PAGE_TYPE_OPS(uname, lname) \
I think this is a bit complex, and a bit of a pain to update as we add
new page types. How about this?
return (int)page_type < -128;
(I'm open to appropriate #defines to make this more obvious that it's ~0x7F)
