[rfc 13/18] slub: Add functions to manage per cpu freelists

[Christoph Lameter <cl@linux.com>]

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Add a couple of functions that will be used later to manage the per cpu
freelists.

Signed-off-by: Christoph Lameter <cl@linux.com>


---
 mm/slub.c |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2011-11-10 13:50:40.250719277 -0600
+++ linux-2.6/mm/slub.c	2011-11-10 13:56:05.602531668 -0600
@@ -2111,6 +2111,58 @@ static inline void *new_slab_objects(str
 }
 
 /*
+ * Retrieve pointer to the current freelist and
+ * zap the per cpu object list.
+ *
+ * Returns NULL if there was no object on the freelist.
+ */
+void *get_cpu_objects(struct kmem_cache *s)
+{
+	void *freelist;
+	unsigned long tid;
+
+	do {
+		struct kmem_cache_cpu *c = this_cpu_ptr(s->cpu_slab);
+
+		tid = c->tid;
+		barrier();
+		freelist = c->freelist;
+		if (!freelist)
+			return NULL;
+
+	} while (!this_cpu_cmpxchg_double(s->cpu_slab->freelist, s->cpu_slab->tid,
+			freelist, tid,
+			NULL, next_tid(tid)));
+
+	return freelist;
+}
+
+/*
+ * Set the per cpu object list to the freelist. The page must
+ * be frozen.
+ *
+ * Page will be unfrozen (and the freelist object put onto the pages freelist)
+ * if the per cpu freelist has been used in the meantime.
+ */
+static inline void put_cpu_objects(struct kmem_cache *s,
+				struct page *page, void *freelist)
+{
+	unsigned long tid;
+
+	tid = this_cpu_read(s->cpu_slab->tid);
+	barrier();
+
+	VM_BUG_ON(!page->frozen);
+	if (!irqsafe_cpu_cmpxchg_double(s->cpu_slab->freelist, s->cpu_slab->tid,
+		NULL, tid, freelist, next_tid(tid)))
+
+		/*
+		 * There was an intervening free or alloc. Cannot free to the
+		 * per cpu queue. Must unfreeze page.
+		 */
+		deactivate_slab(s, page, freelist);
+}
+/*
  * Check the page->freelist of a page and either transfer the freelist to the per cpu freelist
  * or deactivate the page.
  *

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