[PATCH] shrink struct page

Reduce the size of the pageframe for NR_CPUS>4, CONFIG_PREEMPT back to the
minimal size by unionising both ->private and ->mapping with the pagetable
lock.

It uses an anonymous struct and hence requires gcc-3.x.

Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 22 insertions, 19 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7ff54242c5d7..df80e63903b5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -223,24 +223,27 @@ struct page {
                                          * & limit reverse map searches.
                                          */
         union {
-                unsigned long private;  /* Mapping-private opaque data:
-                                         * usually used for buffer_heads
-                                         * if PagePrivate set; used for
-                                         * swp_entry_t if PageSwapCache
-                                         * When page is free, this indicates
-                                         * order in the buddy system.
-                                         */
+            struct {
+                unsigned long private;          /* Mapping-private opaque data:
+                                                 * usually used for buffer_heads
+                                                 * if PagePrivate set; used for
+                                                 * swp_entry_t if PageSwapCache.
+                                                 * When page is free, this
+                                                 * indicates order in the buddy
+                                                 * system.
+                                                 */
+                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:
+                                                 * see PAGE_MAPPING_ANON below.
+                                                 */
+            };
 #if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
-                spinlock_t ptl;
+            spinlock_t ptl;
 #endif
-        } u;
-        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:
-                                         * see PAGE_MAPPING_ANON below.
-                                         */
+        };
         pgoff_t index;                  /* Our offset within mapping. */
         struct list_head lru;           /* Pageout list, eg. active_list
                                          * protected by zone->lru_lock !
@@ -261,8 +264,8 @@ struct page {
 #endif /* WANT_PAGE_VIRTUAL */
 };
 
-#define page_private(page)              ((page)->u.private)
-#define set_page_private(page, v)       ((page)->u.private = (v))
+#define page_private(page)              ((page)->private)
+#define set_page_private(page, v)       ((page)->private = (v))
 
 /*
  * FIXME: take this include out, include page-flags.h in
@@ -815,7 +818,7 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
  * overflow into the next struct page (as it might with DEBUG_SPINLOCK).
  * When freeing, reset page->mapping so free_pages_check won't complain.
  */
-#define __pte_lockptr(page)     &((page)->u.ptl)
+#define __pte_lockptr(page)     &((page)->ptl)
 #define pte_lock_init(_page)    do {                                    \
         spin_lock_init(__pte_lockptr(_page));                           \
 } while (0)