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Subject[PATCH] /proc/kpagecount: return 0 for special pages that are never mapped
Date
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@oracle.com>
---
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) \
static __always_inline int Page##uname(struct page *page) \
{ \
--
1.8.3.1
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