mm:add KPF_ZERO_PAGE flag for /proc/kpageflags

Add KPF_ZERO_PAGE flag for zero_page, so that userspace processes can
detect zero_page in /proc/kpageflags, and then do memory analysis more
accurately.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 3 deletions

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 1e3187da1fed..7eee2d8b97d9 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -5,6 +5,7 @@
 #include <linux/ksm.h>
 #include <linux/mm.h>
 #include <linux/mmzone.h>
+#include <linux/huge_mm.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/hugetlb.h>
@@ -121,9 +122,18 @@ u64 stable_page_flags(struct page *page)
          * just checks PG_head/PG_tail, so we need to check PageLRU/PageAnon
          * to make sure a given page is a thp, not a non-huge compound page.
          */
-        else if (PageTransCompound(page) && (PageLRU(compound_head(page)) ||
-                                             PageAnon(compound_head(page))))
-                u |= 1 << KPF_THP;
+        else if (PageTransCompound(page)) {
+                struct page *head = compound_head(page);
+
+                if (PageLRU(head) || PageAnon(head))
+                        u |= 1 << KPF_THP;
+                else if (is_huge_zero_page(head)) {
+                        u |= 1 << KPF_ZERO_PAGE;
+                        u |= 1 << KPF_THP;
+                }
+        } else if (is_zero_pfn(page_to_pfn(page)))
+                u |= 1 << KPF_ZERO_PAGE;
+
 
         /*
          * Caveats on high order pages: page->_count will only be set