slab: Remove folio references from kfree_rcu_sheaf()

In preparation for splitting struct slab from struct page and struct
folio, remove mentions of struct folio from this function.  Since
we don't need to handle large kmalloc objects specially here, we
can just use virt_to_slab().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20251113000932.1589073-12-willy@infradead.org
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: Matthew Wilcox (Oracle)

mm/slab_common.c

@@ -1615,17 +1615,15 @@ static void kfree_rcu_work(struct work_struct *work)
 static bool kfree_rcu_sheaf(void *obj)
 {
 	struct kmem_cache *s;
-	struct folio *folio;
 	struct slab *slab;
 
 	if (is_vmalloc_addr(obj))
 		return false;
 
-	folio = virt_to_folio(obj);
-	if (unlikely(!folio_test_slab(folio)))
+	slab = virt_to_slab(obj);
+	if (unlikely(!slab))
 		return false;
 
-	slab = folio_slab(folio);
 	s = slab->slab_cache;
 	if (s->cpu_sheaves) {
 		if (likely(!IS_ENABLED(CONFIG_NUMA) ||