SLUB: Define functions for cpu slab handling instead of using PageActive

Use inline functions to access the per cpu bit.  Intoduce the notion of
"freezing" a slab to make things more understandable.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 19 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 022c1b4d74d4..ce96d485a88f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -78,10 +78,18 @@
  *
  * Overloading of page flags that are otherwise used for LRU management.
  *
- * PageActive           The slab is used as a cpu cache. Allocations
- *                      may be performed from the slab. The slab is not
- *                      on any slab list and cannot be moved onto one.
- *                      The cpu slab may be equipped with an additioanl
+ * PageActive           The slab is frozen and exempt from list processing.
+ *                      This means that the slab is dedicated to a purpose
+ *                      such as satisfying allocations for a specific
+ *                      processor. Objects may be freed in the slab while
+ *                      it is frozen but slab_free will then skip the usual
+ *                      list operations. It is up to the processor holding
+ *                      the slab to integrate the slab into the slab lists
+ *                      when the slab is no longer needed.
+ *
+ *                      One use of this flag is to mark slabs that are
+ *                      used for allocations. Then such a slab becomes a cpu
+ *                      slab. The cpu slab may be equipped with an additional
  *                      lockless_freelist that allows lockless access to
  *                      free objects in addition to the regular freelist
  *                      that requires the slab lock.
@@ -91,6 +99,21 @@
  *                      the fast path and disables lockless freelists.
  */
 
+static inline int SlabFrozen(struct page *page)
+{
+        return PageActive(page);
+}
+
+static inline void SetSlabFrozen(struct page *page)
+{
+        SetPageActive(page);
+}
+
+static inline void ClearSlabFrozen(struct page *page)
+{
+        ClearPageActive(page);
+}
+
 static inline int SlabDebug(struct page *page)
 {
 #ifdef CONFIG_SLUB_DEBUG
@@ -1135,11 +1158,12 @@ static void remove_partial(struct kmem_cache *s,
  *
  * Must hold list_lock.
  */
-static int lock_and_del_slab(struct kmem_cache_node *n, struct page *page)
+static inline int lock_and_freeze_slab(struct kmem_cache_node *n, struct page *page)
 {
         if (slab_trylock(page)) {
                 list_del(&page->lru);
                 n->nr_partial--;
+                SetSlabFrozen(page);
                 return 1;
         }
         return 0;
@@ -1163,7 +1187,7 @@ static struct page *get_partial_node(struct kmem_cache_node *n)
 
         spin_lock(&n->list_lock);
         list_for_each_entry(page, &n->partial, lru)
-                if (lock_and_del_slab(n, page))
+                if (lock_and_freeze_slab(n, page))
                         goto out;
         page = NULL;
 out:
@@ -1242,10 +1266,11 @@ static struct page *get_partial(struct kmem_cache *s, gfp_t flags, int node)
  *
  * On exit the slab lock will have been dropped.
  */
-static void putback_slab(struct kmem_cache *s, struct page *page)
+static void unfreeze_slab(struct kmem_cache *s, struct page *page)
 {
         struct kmem_cache_node *n = get_node(s, page_to_nid(page));
 
+        ClearSlabFrozen(page);
         if (page->inuse) {
 
                 if (page->freelist)
@@ -1296,9 +1321,7 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page, int cpu)
                 page->inuse--;
         }
         s->cpu_slab[cpu] = NULL;
-        ClearPageActive(page);
-
-        putback_slab(s, page);
+        unfreeze_slab(s, page);
 }
 
 static void flush_slab(struct kmem_cache *s, struct page *page, int cpu)
@@ -1389,9 +1412,7 @@ another_slab:
 new_slab:
         page = get_partial(s, gfpflags, node);
         if (page) {
-have_slab:
                 s->cpu_slab[cpu] = page;
-                SetPageActive(page);
                 goto load_freelist;
         }
 
@@ -1421,7 +1442,9 @@ have_slab:
                         flush_slab(s, s->cpu_slab[cpu], cpu);
                 }
                 slab_lock(page);
-                goto have_slab;
+                SetSlabFrozen(page);
+                s->cpu_slab[cpu] = page;
+                goto load_freelist;
         }
         return NULL;
 debug:
@@ -1508,11 +1531,7 @@ checks_ok:
         page->freelist = object;
         page->inuse--;
 
-        if (unlikely(PageActive(page)))
-                /*
-                 * Cpu slabs are never on partial lists and are
-                 * never freed.
-                 */
+        if (unlikely(SlabFrozen(page)))
                 goto out_unlock;
 
         if (unlikely(!page->inuse))
@@ -1544,7 +1563,7 @@ slab_empty:
 debug:
         if (!free_object_checks(s, page, x))
                 goto out_unlock;
-        if (!PageActive(page) && !page->freelist)
+        if (!SlabFrozen(page) && !page->freelist)
                 remove_full(s, page);
         if (s->flags & SLAB_STORE_USER)
                 set_track(s, x, TRACK_FREE, addr);