mm/memcg: alignment memcg_data define condition

From: "Alex Shi (Tencent)" <[email protected]>

commit 21c690a349ba ("mm: introduce slabobj_ext to support slab object extensions") changed the folio/page->memcg_data define condition from MEMCG to SLAB_OBJ_EXT. And selected SLAB_OBJ_EXT for MEMCG, just for SLAB_MATCH(memcg_data, obj_exts), even no other relationship between them.

Above action make memcg_data exposed and include SLAB_OBJ_EXT for !MEMCG. That's incorrect in logcial and pay on code size.

So let's remove SLAB_OBJ_EXT from MEMCG and as Vlastimil Babka suggested, add _unused_slab_obj_ext for SLAB_MATCH for slab.obj_exts while !MEMCG. That could resolve the match issue, clean up the feature logical and save the unnessary code adding.

Signed-off-by Alex Shi (Tencent) <[email protected]>

Cc Randy Dunlap <[email protected]>

Cc Yoann Congal <[email protected]>

Cc Masahiro Yamada <[email protected]>

Cc Petr Mladek <[email protected]>

Cc Suren Baghdasaryan <[email protected]>

Cc Vlastimil Babka <[email protected]>

---
 include/linux/mm_types.h | 8 ++++++--
 init/Kconfig             | 1 -
 mm/slab.h                | 4 ++++
 3 files changed, 10 insertions(+), 3 deletions(-)

include/linux/mm_types.h +6 -2

index ef09c4eef6d3..4ac3abc673d3 100644
@@ -180,8 +180,10 @@ struct page {
 	/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
 	atomic_t _refcount;
 
-#ifdef CONFIG_SLAB_OBJ_EXT
+#ifdef CONFIG_MEMCG
 	unsigned long memcg_data;
+#elif defined(CONFIG_SLAB_OBJ_EXT)
+	unsigned long _unused_slab_obj_ext;
 #endif
 
 	/*

@@ -343,8 +345,10 @@ struct folio {
 			};
 			atomic_t _mapcount;
 			atomic_t _refcount;
-#ifdef CONFIG_SLAB_OBJ_EXT
+#ifdef CONFIG_MEMCG
 			unsigned long memcg_data;
+#elif defined(CONFIG_SLAB_OBJ_EXT)
+			unsigned long _unused_slab_obj_ext;
 #endif
 #if defined(WANT_PAGE_VIRTUAL)
 			void *virtual;

init/Kconfig +0 -1

index 26bf8bb0a7ce..61e43ac9fe75 100644
@@ -965,7 +965,6 @@ config MEMCG
 	bool "Memory controller"
 	select PAGE_COUNTER
 	select EVENTFD
-	select SLAB_OBJ_EXT
 	help
 	  Provides control over the memory footprint of tasks in a cgroup.
 

mm/slab.h +4 -0

index 3586e6183224..8ffdd4f315f8 100644
@@ -98,7 +98,11 @@ SLAB_MATCH(flags, __page_flags);
 SLAB_MATCH(compound_head, slab_cache);	/* Ensure bit 0 is clear */
 SLAB_MATCH(_refcount, __page_refcount);
 #ifdef CONFIG_SLAB_OBJ_EXT
+#ifdef CONFIG_MEMCG
 SLAB_MATCH(memcg_data, obj_exts);
+#else
+SLAB_MATCH(_unused_slab_obj_ext, obj_exts);
+#endif
 #endif
 #undef SLAB_MATCH
 static_assert(sizeof(struct slab) <= sizeof(struct page));