From: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx> Subject: /proc/kpagecount: return 0 for special pages that are never mapped 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. [anthony.yznaga@xxxxxxxxxx: incorporate feedback from Matthew Wilcox] Link: http://lkml.kernel.org/r/1544481313-27318-1-git-send-email-anthony.yznaga@xxxxxxxxxx Link: http://lkml.kernel.org/r/1543963526-27917-1-git-send-email-anthony.yznaga@xxxxxxxxxx Signed-off-by: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Acked-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Miles Chen <miles.chen@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/fs/proc/page.c~proc-kpagecount-return-0-for-special-pages-that-are-never-mapped +++ a/fs/proc/page.c @@ -46,7 +46,7 @@ static ssize_t kpagecount_read(struct fi 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); --- a/include/linux/page-flags.h~proc-kpagecount-return-0-for-special-pages-that-are-never-mapped +++ a/include/linux/page-flags.h @@ -669,6 +669,7 @@ PAGEFLAG_FALSE(DoubleMap) #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 @@ PAGEFLAG_FALSE(DoubleMap) #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) \ { \ _
