mm: Convert __ksize() to struct slab

In SLUB, use folios, and struct slab to access slab_cache field.
In SLOB, use folios to properly resolve pointers beyond
PAGE_SIZE offset of the object.

[ vbabka@suse.cz: use folios, and only convert folio_test_slab() == true
  folios to struct slab ]
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <guro@fb.com>

mm/slob.c

@@ -570,7 +570,7 @@ EXPORT_SYMBOL(kfree);
 /* can't use ksize for kmem_cache_alloc memory, only kmalloc */
 size_t __ksize(const void *block)
 {
-	struct page *sp;
+	struct folio *folio;
 	int align;
 	unsigned int *m;
 
@@ -578,9 +578,9 @@ size_t __ksize(const void *block)
 	if (unlikely(block == ZERO_SIZE_PTR))
 		return 0;
 
-	sp = virt_to_page(block);
-	if (unlikely(!PageSlab(sp)))
-		return page_size(sp);
+	folio = virt_to_folio(block);
+	if (unlikely(!folio_test_slab(folio)))
+		return folio_size(folio);
 
 	align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
 	m = (unsigned int *)(block - align);

mm/slub.c

@@ -4527,19 +4527,17 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 
 size_t __ksize(const void *object)
 {
-	struct page *page;
+	struct folio *folio;
 
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return 0;
 
-	page = virt_to_head_page(object);
+	folio = virt_to_folio(object);
 
-	if (unlikely(!PageSlab(page))) {
-		WARN_ON(!PageCompound(page));
-		return page_size(page);
-	}
+	if (unlikely(!folio_test_slab(folio)))
+		return folio_size(folio);
 
-	return slab_ksize(page->slab_cache);
+	return slab_ksize(folio_slab(folio)->slab_cache);
 }
 EXPORT_SYMBOL(__ksize);