/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>

4 files changed, 6 insertions, 7 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;
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 19724e6ebd26..597695523679 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -593,6 +593,8 @@ static inline void __ClearPageBuddy(struct page *page)
         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)
diff --git a/mm/internal.h b/mm/internal.h
index ad9400d759c8..b95952c2faec 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -148,9 +148,6 @@ extern int __isolate_free_page(struct page *page, unsigned int order);
 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
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c46b75d14b6f..c7332a4bc8db 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7152,7 +7152,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 }
 #endif
 
-#ifdef CONFIG_MEMORY_FAILURE
 bool is_free_buddy_page(struct page *page)
 {
         struct zone *zone = page_zone(page);
@@ -7171,4 +7170,3 @@ bool is_free_buddy_page(struct page *page)
 
         return order < MAX_ORDER;
 }
-#endif