Merge branch 'linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci

[~andy/linux] / include / linux / mm_types.h

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3e01a19a91e8025f6f6f7499369071af53aef947..5b42f1b34eb74b59964f9a717d436cad44481c05 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -62,10 +62,23 @@ struct page {
                        struct {
 
                                union {
-                                       atomic_t _mapcount;     /* Count of ptes mapped in mms,
-                                                        * to show when page is mapped
-                                                        * & limit reverse map searches.
-                                                        */
+                                       /*
+                                        * Count of ptes mapped in
+                                        * mms, to show when page is
+                                        * mapped & limit reverse map
+                                        * searches.
+                                        *
+                                        * Used also for tail pages
+                                        * refcounting instead of
+                                        * _count. Tail pages cannot
+                                        * be mapped and keeping the
+                                        * tail page _count zero at
+                                        * all times guarantees
+                                        * get_page_unless_zero() will
+                                        * never succeed on tail
+                                        * pages.
+                                        */
+                                       atomic_t _mapcount;
 
                                        struct {
                                                unsigned inuse:16;