slab: Remove folio references from kvfree_rcu_cb()

Remove conversions from folio to page and folio to slab.  This is
preparation for separately allocated struct slab from struct page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20251113000932.1589073-8-willy@infradead.org
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: Matthew Wilcox (Oracle)

mm/slub.c

@@ -6771,7 +6771,7 @@ static void free_large_kmalloc(struct page *page, void *object)
 void kvfree_rcu_cb(struct rcu_head *head)
 {
 	void *obj = head;
-	struct folio *folio;
+	struct page *page;
 	struct slab *slab;
 	struct kmem_cache *s;
 	void *slab_addr;
@@ -6782,20 +6782,20 @@ void kvfree_rcu_cb(struct rcu_head *head)
 		return;
 	}
 
-	folio = virt_to_folio(obj);
-	if (!folio_test_slab(folio)) {
+	page = virt_to_page(obj);
+	slab = page_slab(page);
+	if (!slab) {
 		/*
 		 * rcu_head offset can be only less than page size so no need to
-		 * consider folio order
+		 * consider allocation order
 		 */
 		obj = (void *) PAGE_ALIGN_DOWN((unsigned long)obj);
-		free_large_kmalloc(&folio->page, obj);
+		free_large_kmalloc(page, obj);
 		return;
 	}
 
-	slab = folio_slab(folio);
 	s = slab->slab_cache;
-	slab_addr = folio_address(folio);
+	slab_addr = slab_address(slab);
 
 	if (is_kfence_address(obj)) {
 		obj = kfence_object_start(obj);