/proc/kpageflags: return KPF_BUDDY for "tail" buddy pages

Currently /proc/kpageflags returns nothing for "tail" buddy pages, which
is inconvenient when grasping how free pages are distributed.  This
patch sets KPF_BUDDY for such pages.

With this patch:

  $ grep MemFree /proc/meminfo ; tools/vm/page-types -b buddy
  MemFree:         3134992 kB
               flags      page-count       MB  symbolic-flags                     long-symbolic-flags
  0x0000000000000400          779272     3044  __________B_______________________________ buddy
  0x0000000000000c00            4385       17  __________BM______________________________ buddy,mmap
               total          783657     3061

783657 pages is 3134628 kB (roughly consistent with the global counter,)
so it's OK.

[akpm@linux-foundation.org: update comment, per Naoya]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>>
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, 4 insertions, 2 deletions

diff --git a/fs/proc/page.c b/fs/proc/page.c
index b2855eea5405..0be626d85331 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -103,9 +103,9 @@ u64 stable_page_flags(struct page *page)
          * pseudo flags for the well known (anonymous) memory mapped pages
          *
          * Note that page->_mapcount is overloaded in SLOB/SLUB/SLQB, so the
-         * simple test in page_mapcount() is not enough.
+         * simple test in page_mapped() is not enough.
          */
-        if (!PageSlab(page) && page_mapcount(page))
+        if (!PageSlab(page) && page_mapped(page))
                 u |= 1 << KPF_MMAP;
         if (PageAnon(page))
                 u |= 1 << KPF_ANON;
@@ -148,6 +148,8 @@ u64 stable_page_flags(struct page *page)
          */
         if (PageBuddy(page))
                 u |= 1 << KPF_BUDDY;
+        else if (page_count(page) == 0 && is_free_buddy_page(page))
+                u |= 1 << KPF_BUDDY;
 
         if (PageBalloon(page))
                 u |= 1 << KPF_BALLOON;