mm/slab.c use list_first_entry_or_null()

Simplify the code with list_first_entry_or_null().
Signed-off-by: NGeliang Tang <geliangtang@163.com>
Acked-by: NChristoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/slab.c

@@ -2791,18 +2791,18 @@ static void *cache_alloc_refill(struct kmem_cache *cachep, gfp_t flags,
 	}
 
 	while (batchcount > 0) {
-		struct list_head *entry;
 		struct page *page;
 		/* Get slab alloc is to come from. */
-		entry = n->slabs_partial.next;
-		if (entry == &n->slabs_partial) {
+		page = list_first_entry_or_null(&n->slabs_partial,
+				struct page, lru);
+		if (!page) {
 			n->free_touched = 1;
-			entry = n->slabs_free.next;
-			if (entry == &n->slabs_free)
+			page = list_first_entry_or_null(&n->slabs_free,
+					struct page, lru);
+			if (!page)
 				goto must_grow;
 		}
 
-		page = list_entry(entry, struct page, lru);
 		check_spinlock_acquired(cachep);
 
 		/*
@@ -3085,7 +3085,6 @@ static void *fallback_alloc(struct kmem_cache *cache, gfp_t flags)
 static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
 				int nodeid)
 {
-	struct list_head *entry;
 	struct page *page;
 	struct kmem_cache_node *n;
 	void *obj;
@@ -3098,15 +3097,16 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
 retry:
 	check_irq_off();
 	spin_lock(&n->list_lock);
-	entry = n->slabs_partial.next;
-	if (entry == &n->slabs_partial) {
+	page = list_first_entry_or_null(&n->slabs_partial,
+			struct page, lru);
+	if (!page) {
 		n->free_touched = 1;
-		entry = n->slabs_free.next;
-		if (entry == &n->slabs_free)
+		page = list_first_entry_or_null(&n->slabs_free,
+				struct page, lru);
+		if (!page)
 			goto must_grow;
 	}
 
-	page = list_entry(entry, struct page, lru);
 	check_spinlock_acquired_node(cachep, nodeid);
 
 	STATS_INC_NODEALLOCS(cachep);