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-rw-r--r--include/linux/mm_types.h87
1 files changed, 59 insertions, 28 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index e5fb2a7..3d76a43 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -30,24 +30,60 @@ struct address_space;
* moment. Note that we have no way to track which tasks are using
* a page, though if it is a pagecache page, rmap structures can tell us
* who is mapping it.
+ *
+ * The objects in struct page are organized in double word blocks in
+ * order to allows us to use atomic double word operations on portions
+ * of struct page. That is currently only used by slub but the arrangement
+ * allows the use of atomic double word operations on the flags/mapping
+ * and lru list pointers also.
*/
struct page {
+ /* First double word block */
unsigned long flags; /* Atomic flags, some possibly
* updated asynchronously */
- atomic_t _count; /* Usage count, see below. */
+ 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.
+ */
+ /* Second double word */
union {
- atomic_t _mapcount; /* Count of ptes mapped in mms,
- * to show when page is mapped
- * & limit reverse map searches.
+ struct {
+ pgoff_t index; /* Our offset within mapping. */
+ atomic_t _mapcount; /* Count of ptes mapped in mms,
+ * to show when page is mapped
+ * & limit reverse map searches.
+ */
+ atomic_t _count; /* Usage count, see below. */
+ };
+
+ struct { /* SLUB cmpxchg_double area */
+ void *freelist;
+ union {
+ unsigned long counters;
+ struct {
+ unsigned inuse:16;
+ unsigned objects:15;
+ unsigned frozen:1;
+ /*
+ * Kernel may make use of this field even when slub
+ * uses the rest of the double word!
*/
- struct { /* SLUB */
- unsigned inuse:16;
- unsigned objects:15;
- unsigned frozen:1;
+ atomic_t _count;
+ };
+ };
};
};
+
+ /* Third double word block */
+ struct list_head lru; /* Pageout list, eg. active_list
+ * protected by zone->lru_lock !
+ */
+
+ /* Remainder is not double word aligned */
union {
- struct {
unsigned long private; /* Mapping-private opaque data:
* usually used for buffer_heads
* if PagePrivate set; used for
@@ -55,27 +91,13 @@ struct page {
* indicates order in the buddy
* system if PG_buddy is set.
*/
- 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 USE_SPLIT_PTLOCKS
- spinlock_t ptl;
+ spinlock_t ptl;
#endif
- struct kmem_cache *slab; /* SLUB: Pointer to slab */
- struct page *first_page; /* Compound tail pages */
+ struct kmem_cache *slab; /* SLUB: Pointer to slab */
+ struct page *first_page; /* Compound tail pages */
};
- union {
- pgoff_t index; /* Our offset within mapping. */
- void *freelist; /* SLUB: freelist req. slab lock */
- };
- struct list_head lru; /* Pageout list, eg. active_list
- * protected by zone->lru_lock !
- */
+
/*
* On machines where all RAM is mapped into kernel address space,
* we can simply calculate the virtual address. On machines with
@@ -101,7 +123,16 @@ struct page {
*/
void *shadow;
#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.
+ */
+#if defined(CONFIG_SLUB) && defined(CONFIG_CMPXCHG_LOCAL)
+ __attribute__((__aligned__(2*sizeof(unsigned long))))
+#endif
+;
typedef unsigned long __nocast vm_flags_t;
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