slab: objext: introduce objext_flags as extension to page_memcg_data_flags

Introduce objext_flags to store additional objext flags unrelated to memcg.

Link: https://lkml.kernel.org/r/20240321163705.3067592-10-surenb@google.comSigned-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Kees Cook <keescook@chromium.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alex Gaynor <alex.gaynor@gmail.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andreas Hindborg <a.hindborg@samsung.com>
Cc: Benno Lossin <benno.lossin@proton.me>
Cc: "Björn Roy Baron" <bjorn3_gh@protonmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Gary Guo <gary@garyguo.net>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -357,7 +357,22 @@ enum page_memcg_data_flags {
 	__NR_MEMCG_DATA_FLAGS  = (1UL << 2),
 };
 
-#define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1)
+#define __FIRST_OBJEXT_FLAG	__NR_MEMCG_DATA_FLAGS
+
+#else /* CONFIG_MEMCG */
+
+#define __FIRST_OBJEXT_FLAG	(1UL << 0)
+
+#endif /* CONFIG_MEMCG */
+
+enum objext_flags {
+	/* the next bit after the last actual flag */
+	__NR_OBJEXTS_FLAGS  = __FIRST_OBJEXT_FLAG,
+};
+
+#define OBJEXTS_FLAGS_MASK (__NR_OBJEXTS_FLAGS - 1)
+
+#ifdef CONFIG_MEMCG
 
 static inline bool folio_memcg_kmem(struct folio *folio);
 
@@ -391,7 +406,7 @@ static inline struct mem_cgroup *__folio_memcg(struct folio *folio)
 	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJEXTS, folio);
 	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_KMEM, folio);
 
-	return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+	return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
 }
 
 /*
@@ -412,7 +427,7 @@ static inline struct obj_cgroup *__folio_objcg(struct folio *folio)
 	VM_BUG_ON_FOLIO(memcg_data & MEMCG_DATA_OBJEXTS, folio);
 	VM_BUG_ON_FOLIO(!(memcg_data & MEMCG_DATA_KMEM), folio);
 
-	return (struct obj_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+	return (struct obj_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
 }
 
 /*
@@ -469,11 +484,11 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
 	if (memcg_data & MEMCG_DATA_KMEM) {
 		struct obj_cgroup *objcg;
 
-		objcg = (void *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+		objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
 		return obj_cgroup_memcg(objcg);
 	}
 
-	return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+	return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
 }
 
 /*
@@ -512,11 +527,11 @@ static inline struct mem_cgroup *folio_memcg_check(struct folio *folio)
 	if (memcg_data & MEMCG_DATA_KMEM) {
 		struct obj_cgroup *objcg;
 
-		objcg = (void *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+		objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
 		return obj_cgroup_memcg(objcg);
 	}
 
-	return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
+	return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
 }
 
 static inline struct mem_cgroup *page_memcg_check(struct page *page)

mm/slab.h

@@ -554,11 +554,8 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
 	VM_BUG_ON_PAGE(obj_exts && !(obj_exts & MEMCG_DATA_OBJEXTS),
 							slab_page(slab));
 	VM_BUG_ON_PAGE(obj_exts & MEMCG_DATA_KMEM, slab_page(slab));
-
-	return (struct slabobj_ext *)(obj_exts & ~MEMCG_DATA_FLAGS_MASK);
-#else
-	return (struct slabobj_ext *)obj_exts;
 #endif
+	return (struct slabobj_ext *)(obj_exts & ~OBJEXTS_FLAGS_MASK);
 }
 
 #else /* CONFIG_SLAB_OBJ_EXT */