Merge branch 'slab/for-6.2/fit_rcu_head' into slab/for-next

A series by myself to reorder fields in struct slab to allow the
embedded rcu_head to grow (for debugging purposes). Requires changes to
isolate_movable_page() to skip slab pages which can otherwise become
false-positive __PageMovable due to its use of low bits in
page->mapping.

1 files changed, 32 insertions, 22 deletions

diff --git a/mm/slab.h b/mm/slab.h
index 19e1baac807c..8c4aafb00bd6 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -11,37 +11,43 @@ struct slab {
 
 #if defined(CONFIG_SLAB)
 
+	struct kmem_cache *slab_cache;
 	union {
-		struct list_head slab_list;
+		struct {
+			struct list_head slab_list;
+			void *freelist;	/* array of free object indexes */
+			void *s_mem;	/* first object */
+		};
 		struct rcu_head rcu_head;
 	};
-	struct kmem_cache *slab_cache;
-	void *freelist;	/* array of free object indexes */
-	void *s_mem;	/* first object */
 	unsigned int active;
 
 #elif defined(CONFIG_SLUB)
 
-	union {
-		struct list_head slab_list;
-		struct rcu_head rcu_head;
-#ifdef CONFIG_SLUB_CPU_PARTIAL
-		struct {
-			struct slab *next;
-			int slabs;	/* Nr of slabs left */
-		};
-#endif
-	};
 	struct kmem_cache *slab_cache;
-	/* Double-word boundary */
-	void *freelist;		/* first free object */
 	union {
-		unsigned long counters;
 		struct {
-			unsigned inuse:16;
-			unsigned objects:15;
-			unsigned frozen:1;
+			union {
+				struct list_head slab_list;
+#ifdef CONFIG_SLUB_CPU_PARTIAL
+				struct {
+					struct slab *next;
+					int slabs;	/* Nr of slabs left */
+				};
+#endif
+			};
+			/* Double-word boundary */
+			void *freelist;		/* first free object */
+			union {
+				unsigned long counters;
+				struct {
+					unsigned inuse:16;
+					unsigned objects:15;
+					unsigned frozen:1;
+				};
+			};
 		};
+		struct rcu_head rcu_head;
 	};
 	unsigned int __unused;
 
@@ -66,9 +72,10 @@ struct slab {
 #define SLAB_MATCH(pg, sl)						\
 	static_assert(offsetof(struct page, pg) == offsetof(struct slab, sl))
 SLAB_MATCH(flags, __page_flags);
-SLAB_MATCH(compound_head, slab_list);	/* Ensure bit 0 is clear */
 #ifndef CONFIG_SLOB
-SLAB_MATCH(rcu_head, rcu_head);
+SLAB_MATCH(compound_head, slab_cache);	/* Ensure bit 0 is clear */
+#else
+SLAB_MATCH(compound_head, slab_list);	/* Ensure bit 0 is clear */
 #endif
 SLAB_MATCH(_refcount, __page_refcount);
 #ifdef CONFIG_MEMCG
@@ -76,6 +83,9 @@ SLAB_MATCH(memcg_data, memcg_data);
 #endif
 #undef SLAB_MATCH
 static_assert(sizeof(struct slab) <= sizeof(struct page));
+#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && defined(CONFIG_SLUB)
+static_assert(IS_ALIGNED(offsetof(struct slab, freelist), 2*sizeof(void *)));
+#endif
 
 /**
  * folio_slab - Converts from folio to slab.