mm/zsmalloc: remove get_zspage_mapping()

Actually we seldom use the class_idx returned from get_zspage_mapping(),
only the zspage->fullness is useful, just use zspage->fullness to remove
this helper.

Note zspage->fullness is not stable outside pool->lock, remove redundant
"VM_BUG_ON(fullness != ZS_INUSE_RATIO_0)" in async_free_zspage() since we
already have the same VM_BUG_ON() in __free_zspage(), which is safe to
access zspage->fullness with pool->lock held.

Link: https://lkml.kernel.org/r/20240220-b4-zsmalloc-cleanup-v1-3-5c5ee4ccdd87@bytedance.comSigned-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/zsmalloc.c

@@ -470,16 +470,6 @@ static inline void set_freeobj(struct zspage *zspage, unsigned int obj)
 	zspage->freeobj = obj;
 }
 
-static void get_zspage_mapping(struct zspage *zspage,
-			       unsigned int *class_idx,
-			       int *fullness)
-{
-	BUG_ON(zspage->magic != ZSPAGE_MAGIC);
-
-	*fullness = zspage->fullness;
-	*class_idx = zspage->class;
-}
-
 static struct size_class *zspage_class(struct zs_pool *pool,
 				       struct zspage *zspage)
 {
@@ -708,12 +698,10 @@ static void remove_zspage(struct size_class *class, struct zspage *zspage)
  */
 static int fix_fullness_group(struct size_class *class, struct zspage *zspage)
 {
-	int class_idx;
-	int currfg, newfg;
+	int newfg;
 
-	get_zspage_mapping(zspage, &class_idx, &currfg);
 	newfg = get_fullness_group(class, zspage);
-	if (newfg == currfg)
+	if (newfg == zspage->fullness)
 		goto out;
 
 	remove_zspage(class, zspage);
@@ -835,15 +823,11 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
 				struct zspage *zspage)
 {
 	struct page *page, *next;
-	int fg;
-	unsigned int class_idx;
-
-	get_zspage_mapping(zspage, &class_idx, &fg);
 
 	assert_spin_locked(&pool->lock);
 
 	VM_BUG_ON(get_zspage_inuse(zspage));
-	VM_BUG_ON(fg != ZS_INUSE_RATIO_0);
+	VM_BUG_ON(zspage->fullness != ZS_INUSE_RATIO_0);
 
 	next = page = get_first_page(zspage);
 	do {
@@ -1857,8 +1841,6 @@ static void async_free_zspage(struct work_struct *work)
 {
 	int i;
 	struct size_class *class;
-	unsigned int class_idx;
-	int fullness;
 	struct zspage *zspage, *tmp;
 	LIST_HEAD(free_pages);
 	struct zs_pool *pool = container_of(work, struct zs_pool,
@@ -1879,10 +1861,8 @@ static void async_free_zspage(struct work_struct *work)
 		list_del(&zspage->list);
 		lock_zspage(zspage);
 
-		get_zspage_mapping(zspage, &class_idx, &fullness);
-		VM_BUG_ON(fullness != ZS_INUSE_RATIO_0);
-		class = pool->size_class[class_idx];
 		spin_lock(&pool->lock);
+		class = zspage_class(pool, zspage);
 		__free_zspage(pool, class, zspage);
 		spin_unlock(&pool->lock);
 	}