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;
#endif
}
/*
- * If another subsystem starts using the double word pairing for atomic
- * operations on struct page then it must change the #if to ensure
- * proper alignment of the page struct.
+ * The struct page can be forced to be double word aligned so that atomic ops
+ * on double words work. The SLUB allocator can make use of such a feature.
*/
-#if defined(CONFIG_SLUB) && defined(CONFIG_CMPXCHG_LOCAL)
- __attribute__((__aligned__(2*sizeof(unsigned long))))
+#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
+ __aligned(2 * sizeof(unsigned long))
#endif
;