In the future, we will separate slab, folio and page from each other
and calling virt_to_folio() on an address allocated from slab will
return NULL.  Delay the conversion from struct page to struct slab
until we know we're not dealing with a large kmalloc allocation.
There's a minor win for large kmalloc allocations as we avoid the
compound_head() hidden in virt_to_folio().

This deprecates calling ksize() on memory allocated by alloc_pages().
Today it becomes a warning and support will be removed entirely in
the future.

Introduce large_kmalloc_size() to abstract how we represent the size
of a large kmalloc allocation.  For now, this is the same as
page_size(), but it will change with separately allocated memdescs.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/page-flags.h |  2 +-
 mm/slab.h                  | 10 ++++++++++
 mm/slab_common.c           | 23 ++++++++++++-----------
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 6d5e44968eab..f7a0e4af0c73 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1064,7 +1064,7 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
  * Serialized with zone lock.
  */
 PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted)
-FOLIO_TYPE_OPS(large_kmalloc, large_kmalloc)
+PAGE_TYPE_OPS(LargeKmalloc, large_kmalloc, large_kmalloc)
 
 /**
  * PageHuge - Determine if the page belongs to hugetlbfs
diff --git a/mm/slab.h b/mm/slab.h
index 18cdb8e85273..0422f2acf8c6 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -603,6 +603,16 @@ static inline size_t slab_ksize(const struct kmem_cache *s)
 	return s->size;
 }
 
+static inline unsigned int large_kmalloc_order(const struct page *page)
+{
+	return page[1].flags.f & 0xff;
+}
+
+static inline size_t large_kmalloc_size(const struct page *page)
+{
+	return PAGE_SIZE << large_kmalloc_order(page);
+}
+
 #ifdef CONFIG_SLUB_DEBUG
 void dump_unreclaimable_slab(void);
 #else
diff --git a/mm/slab_common.c b/mm/slab_common.c
index d2824daa98cf..236b4e25fce0 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -997,26 +997,27 @@ void __init create_kmalloc_caches(void)
  */
 size_t __ksize(const void *object)
 {
-	struct folio *folio;
+	const struct page *page;
+	const struct slab *slab;
 
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return 0;
 
-	folio = virt_to_folio(object);
+	page = virt_to_page(object);
 
-	if (unlikely(!folio_test_slab(folio))) {
-		if (WARN_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE))
-			return 0;
-		if (WARN_ON(object != folio_address(folio)))
-			return 0;
-		return folio_size(folio);
-	}
+	if (unlikely(PageLargeKmalloc(page)))
+		return large_kmalloc_size(page);
+
+	slab = page_slab(page);
+	/* Delete this after we're sure there are no users */
+	if (WARN_ON(!slab))
+		return page_size(page);
 
 #ifdef CONFIG_SLUB_DEBUG
-	skip_orig_size_check(folio_slab(folio)->slab_cache, object);
+	skip_orig_size_check(slab->slab_cache, object);
 #endif
 
-	return slab_ksize(folio_slab(folio)->slab_cache);
+	return slab_ksize(slab->slab_cache);
 }
 
 gfp_t kmalloc_fix_flags(gfp_t flags)
-- 
2.47.2