mm: improve comment on page->mapping

The comment on page->mapping is terse, and out of date (it does not
mention the possibility of PAGE_MAPPING_MOVABLE).  Instead, point the
interested reader to page-flags.h where there is a much better comment.

Link: http://lkml.kernel.org/r/20171220155552.15884-5-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c2294e6204e80b48eea45531c6775ca9bc13703b..8c3b8cea22ee3c608a5bc1687ee91c23cf2b4bbe 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -50,15 +50,9 @@ struct page {
        unsigned long flags;            /* Atomic flags, some possibly
                                         * updated asynchronously */
        union {
-               struct address_space *mapping;  /* If low bit clear, points to
-                                                * inode address_space, or NULL.
-                                                * If page mapped as anonymous
-                                                * memory, low bit is set, and
-                                                * it points to anon_vma object
-                                                * or KSM private structure. See
-                                                * PAGE_MAPPING_ANON and
-                                                * PAGE_MAPPING_KSM.
-                                                */
+               /* See page-flags.h for the definition of PAGE_MAPPING_FLAGS */
+               struct address_space *mapping;
+
                void *s_mem;                    /* slab first object */
                atomic_t compound_mapcount;     /* first tail page */
                /* page_deferred_list().next     -- second tail page */