commit 832fc1de01aea28255cb11d270679b7f1273f0d7
author Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Thu Mar 17 14:17:41 2016 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Thu Mar 17 15:09:34 2016 -0700
tree ef020cb2a44d1fee4df1359fbb3fc11a08de733b
parent 12580e4b54ba8a1b22ec977c200be0174ca42348

/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>

fs/proc/page.c

diff --git a/fs/proc/page.c b/fs/proc/page.c
index b2855ee..0be626d 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -103,9 +103,9 @@
 	 * 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 @@
 	 */
 	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;

include/linux/page-flags.h

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 19724e6..5976955 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -593,6 +593,8 @@
 	atomic_set(&page->_mapcount, -1);
 }
 
+extern bool is_free_buddy_page(struct page *page);
+
 #define PAGE_BALLOON_MAPCOUNT_VALUE (-256)
 
 static inline int PageBalloon(struct page *page)

mm/internal.h

diff --git a/mm/internal.h b/mm/internal.h
index ad9400d..b95952c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -148,9 +148,6 @@
 extern void __free_pages_bootmem(struct page *page, unsigned long pfn,
 					unsigned int order);
 extern void prep_compound_page(struct page *page, unsigned int order);
-#ifdef CONFIG_MEMORY_FAILURE
-extern bool is_free_buddy_page(struct page *page);
-#endif
 extern int user_min_free_kbytes;
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA

mm/page_alloc.c

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c46b75d..c7332a4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7152,7 +7152,6 @@
 }
 #endif
 
-#ifdef CONFIG_MEMORY_FAILURE
 bool is_free_buddy_page(struct page *page)
 {
 	struct zone *zone = page_zone(page);
@@ -7171,4 +7170,3 @@
 
 	return order < MAX_ORDER;
 }
-#endif