mm/slub: Convert detached_freelist to use a struct slab

This gives us a little bit of extra typesafety as we know that nobody
called virt_to_page() instead of virt_to_head_page().

[ vbabka@suse.cz: Use folio as intermediate step when filtering out
  large kmalloc pages ]
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NRoman Gushchin <guro@fb.com>

mm/slub.c

@@ -3532,7 +3532,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
 EXPORT_SYMBOL(kmem_cache_free);
 
 struct detached_freelist {
-	struct page *page;
+	struct slab *slab;
 	void *tail;
 	void *freelist;
 	int cnt;
@@ -3554,8 +3554,8 @@ static inline void free_nonslab_page(struct page *page, void *object)
 /*
  * This function progressively scans the array with free objects (with
  * a limited look ahead) and extract objects belonging to the same
- * page.  It builds a detached freelist directly within the given
- * page/objects.  This can happen without any need for
+ * slab.  It builds a detached freelist directly within the given
+ * slab/objects.  This can happen without any need for
  * synchronization, because the objects are owned by running process.
  * The freelist is build up as a single linked list in the objects.
  * The idea is, that this detached freelist can then be bulk
@@ -3570,10 +3570,11 @@ int build_detached_freelist(struct kmem_cache *s, size_t size,
 	size_t first_skipped_index = 0;
 	int lookahead = 3;
 	void *object;
-	struct page *page;
+	struct folio *folio;
+	struct slab *slab;
 
 	/* Always re-init detached_freelist */
-	df->page = NULL;
+	df->slab = NULL;
 
 	do {
 		object = p[--size];
@@ -3583,17 +3584,19 @@ int build_detached_freelist(struct kmem_cache *s, size_t size,
 	if (!object)
 		return 0;
 
-	page = virt_to_head_page(object);
+	folio = virt_to_folio(object);
 	if (!s) {
 		/* Handle kalloc'ed objects */
-		if (unlikely(!PageSlab(page))) {
-			free_nonslab_page(page, object);
+		if (unlikely(!folio_test_slab(folio))) {
+			free_nonslab_page(folio_page(folio, 0), object);
 			p[size] = NULL; /* mark object processed */
 			return size;
 		}
 		/* Derive kmem_cache from object */
-		df->s = page->slab_cache;
+		slab = folio_slab(folio);
+		df->s = slab->slab_cache;
 	} else {
+		slab = folio_slab(folio);
 		df->s = cache_from_obj(s, object); /* Support for memcg */
 	}
 
@@ -3605,7 +3608,7 @@ int build_detached_freelist(struct kmem_cache *s, size_t size,
 	}
 
 	/* Start new detached freelist */
-	df->page = page;
+	df->slab = slab;
 	set_freepointer(df->s, object, NULL);
 	df->tail = object;
 	df->freelist = object;
@@ -3617,8 +3620,8 @@ int build_detached_freelist(struct kmem_cache *s, size_t size,
 		if (!object)
 			continue; /* Skip processed objects */
 
-		/* df->page is always set at this point */
-		if (df->page == virt_to_head_page(object)) {
+		/* df->slab is always set at this point */
+		if (df->slab == virt_to_slab(object)) {
 			/* Opportunity build freelist */
 			set_freepointer(df->s, object, df->freelist);
 			df->freelist = object;
@@ -3650,10 +3653,10 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
 		struct detached_freelist df;
 
 		size = build_detached_freelist(s, size, p, &df);
-		if (!df.page)
+		if (!df.slab)
 			continue;
 
-		slab_free(df.s, df.page, df.freelist, df.tail, df.cnt, _RET_IP_);
+		slab_free(df.s, slab_page(df.slab), df.freelist, df.tail, df.cnt, _RET_IP_);
 	} while (likely(size));
 }
 EXPORT_SYMBOL(kmem_cache_free_bulk);