Merge branch 'slab/for-5.18/cleanups' into slab/for-linus

Non-trivial SLUB code cleanups, notably refactoring of deactivate_slab().

mm/slub.c

@@ -2348,10 +2348,10 @@ static void init_kmem_cache_cpus(struct kmem_cache *s)
 static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
 			    void *freelist)
 {
-	enum slab_modes { M_NONE, M_PARTIAL, M_FULL, M_FREE };
+	enum slab_modes { M_NONE, M_PARTIAL, M_FULL, M_FREE, M_FULL_NOLIST };
 	struct kmem_cache_node *n = get_node(s, slab_nid(slab));
-	int lock = 0, free_delta = 0;
-	enum slab_modes l = M_NONE, m = M_NONE;
+	int free_delta = 0;
+	enum slab_modes mode = M_NONE;
 	void *nextfree, *freelist_iter, *freelist_tail;
 	int tail = DEACTIVATE_TO_HEAD;
 	unsigned long flags = 0;
@@ -2393,14 +2393,10 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
 	 * Ensure that the slab is unfrozen while the list presence
 	 * reflects the actual number of objects during unfreeze.
 	 *
-	 * We setup the list membership and then perform a cmpxchg
-	 * with the count. If there is a mismatch then the slab
-	 * is not unfrozen but the slab is on the wrong list.
-	 *
-	 * Then we restart the process which may have to remove
-	 * the slab from the list that we just put it on again
-	 * because the number of objects in the slab may have
-	 * changed.
+	 * We first perform cmpxchg holding lock and insert to list
+	 * when it succeed. If there is mismatch then the slab is not
+	 * unfrozen and number of objects in the slab may have changed.
+	 * Then release lock and retry cmpxchg again.
 	 */
 redo:
 
@@ -2419,61 +2415,52 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
 
 	new.frozen = 0;
 
-	if (!new.inuse && n->nr_partial >= s->min_partial)
-		m = M_FREE;
-	else if (new.freelist) {
-		m = M_PARTIAL;
-		if (!lock) {
-			lock = 1;
-			/*
-			 * Taking the spinlock removes the possibility that
-			 * acquire_slab() will see a slab that is frozen
-			 */
-			spin_lock_irqsave(&n->list_lock, flags);
-		}
+	if (!new.inuse && n->nr_partial >= s->min_partial) {
+		mode = M_FREE;
+	} else if (new.freelist) {
+		mode = M_PARTIAL;
+		/*
+		 * Taking the spinlock removes the possibility that
+		 * acquire_slab() will see a slab that is frozen
+		 */
+		spin_lock_irqsave(&n->list_lock, flags);
+	} else if (kmem_cache_debug_flags(s, SLAB_STORE_USER)) {
+		mode = M_FULL;
+		/*
+		 * This also ensures that the scanning of full
+		 * slabs from diagnostic functions will not see
+		 * any frozen slabs.
+		 */
+		spin_lock_irqsave(&n->list_lock, flags);
 	} else {
-		m = M_FULL;
-		if (kmem_cache_debug_flags(s, SLAB_STORE_USER) && !lock) {
-			lock = 1;
-			/*
-			 * This also ensures that the scanning of full
-			 * slabs from diagnostic functions will not see
-			 * any frozen slabs.
-			 */
-			spin_lock_irqsave(&n->list_lock, flags);
-		}
+		mode = M_FULL_NOLIST;
 	}
 
-	if (l != m) {
-		if (l == M_PARTIAL)
-			remove_partial(n, slab);
-		else if (l == M_FULL)
-			remove_full(s, n, slab);
 
-		if (m == M_PARTIAL)
-			add_partial(n, slab, tail);
-		else if (m == M_FULL)
-			add_full(s, n, slab);
-	}
-
-	l = m;
 	if (!cmpxchg_double_slab(s, slab,
 				old.freelist, old.counters,
 				new.freelist, new.counters,
-				"unfreezing slab"))
+				"unfreezing slab")) {
+		if (mode == M_PARTIAL || mode == M_FULL)
+			spin_unlock_irqrestore(&n->list_lock, flags);
 		goto redo;
+	}
 
-	if (lock)
-		spin_unlock_irqrestore(&n->list_lock, flags);
 
-	if (m == M_PARTIAL)
+	if (mode == M_PARTIAL) {
+		add_partial(n, slab, tail);
+		spin_unlock_irqrestore(&n->list_lock, flags);
 		stat(s, tail);
-	else if (m == M_FULL)
-		stat(s, DEACTIVATE_FULL);
-	else if (m == M_FREE) {
+	} else if (mode == M_FREE) {
 		stat(s, DEACTIVATE_EMPTY);
 		discard_slab(s, slab);
 		stat(s, FREE_SLAB);
+	} else if (mode == M_FULL) {
+		add_full(s, n, slab);
+		spin_unlock_irqrestore(&n->list_lock, flags);
+		stat(s, DEACTIVATE_FULL);
+	} else if (mode == M_FULL_NOLIST) {
+		stat(s, DEACTIVATE_FULL);
 	}
 }
 
@@ -4000,15 +3987,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
 	return 1;
 }
 
-static void set_min_partial(struct kmem_cache *s, unsigned long min)
-{
-	if (min < MIN_PARTIAL)
-		min = MIN_PARTIAL;
-	else if (min > MAX_PARTIAL)
-		min = MAX_PARTIAL;
-	s->min_partial = min;
-}
-
 static void set_cpu_partial(struct kmem_cache *s)
 {
 #ifdef CONFIG_SLUB_CPU_PARTIAL
@@ -4212,7 +4190,8 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 	 * The larger the object size is, the more slabs we want on the partial
 	 * list to avoid pounding the page allocator excessively.
 	 */
-	set_min_partial(s, ilog2(s->size) / 2);
+	s->min_partial = min_t(unsigned long, MAX_PARTIAL, ilog2(s->size) / 2);
+	s->min_partial = max_t(unsigned long, MIN_PARTIAL, s->min_partial);
 
 	set_cpu_partial(s);
 
@@ -5391,7 +5370,7 @@ static ssize_t min_partial_store(struct kmem_cache *s, const char *buf,
 	if (err)
 		return err;
 
-	set_min_partial(s, min);
+	s->min_partial = min;
 	return length;
 }
 SLAB_ATTR(min_partial);