linux-kernel - Re: [PATCH V4 7/8] mm/slab: save memory by allocating slabobj

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Message-ID: <202512231042.EEBUajQY-lkp@intel.com>
Date: Tue, 23 Dec 2025 09:40:39 +0800
From: kernel test robot <lkp@...el.com>
To: Harry Yoo <harry.yoo@...cle.com>, akpm@...ux-foundation.org,
	vbabka@...e.cz
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	andreyknvl@...il.com, cl@...two.org, dvyukov@...gle.com,
	glider@...gle.com, hannes@...xchg.org, linux-mm@...ck.org,
	mhocko@...nel.org, muchun.song@...ux.dev, rientjes@...gle.com,
	roman.gushchin@...ux.dev, ryabinin.a.a@...il.com,
	shakeel.butt@...ux.dev, surenb@...gle.com,
	vincenzo.frascino@....com, yeoreum.yun@....com,
	harry.yoo@...cle.com, tytso@....edu, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, hao.li@...ux.dev
Subject: Re: [PATCH V4 7/8] mm/slab: save memory by allocating slabobj_ext
 array from leftover

Hi Harry,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Harry-Yoo/mm-slab-use-unsigned-long-for-orig_size-to-ensure-proper-metadata-align/20251222-191144
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20251222110843.980347-8-harry.yoo%40oracle.com
patch subject: [PATCH V4 7/8] mm/slab: save memory by allocating slabobj_ext array from leftover
config: x86_64-buildonly-randconfig-001-20251223 (https://download.01.org/0day-ci/archive/20251223/202512231042.EEBUajQY-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251223/202512231042.EEBUajQY-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512231042.EEBUajQY-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/slub.c:2140:33: error: passing 'union codetag_ref' to parameter of incompatible type 'union codetag_ref *'; take the address with &
    2140 |                 if (unlikely(is_codetag_empty(ext->ref))) {
         |                                               ^~~~~~~~
         |                                               &
   include/linux/compiler.h:47:41: note: expanded from macro 'unlikely'
      47 | #  define unlikely(x)   (__branch_check__(x, 0, __builtin_constant_p(x)))
         |                                           ^
   include/linux/compiler.h:32:34: note: expanded from macro '__branch_check__'
      32 |                         ______r = __builtin_expect(!!(x), expect);      \
         |                                                       ^
   include/linux/alloc_tag.h:52:56: note: passing argument to parameter 'ref' here
      52 | static inline bool is_codetag_empty(union codetag_ref *ref)
         |                                                        ^
   mm/slub.c:2140:33: error: passing 'union codetag_ref' to parameter of incompatible type 'union codetag_ref *'; take the address with &
    2140 |                 if (unlikely(is_codetag_empty(ext->ref))) {
         |                                               ^~~~~~~~
         |                                               &
   include/linux/compiler.h:47:68: note: expanded from macro 'unlikely'
      47 | #  define unlikely(x)   (__branch_check__(x, 0, __builtin_constant_p(x)))
         |                                                                      ^
   include/linux/compiler.h:34:19: note: expanded from macro '__branch_check__'
      34 |                                              expect, is_constant);      \
         |                                                      ^~~~~~~~~~~
   include/linux/alloc_tag.h:52:56: note: passing argument to parameter 'ref' here
      52 | static inline bool is_codetag_empty(union codetag_ref *ref)
         |                                                        ^
>> mm/slub.c:2326:16: error: use of undeclared identifier 'MEMCG_DATA_OBJEXTS'
    2326 |                         obj_exts |= MEMCG_DATA_OBJEXTS;
         |                                     ^
   3 errors generated.


vim +/MEMCG_DATA_OBJEXTS +2326 mm/slub.c

  2302	
  2303	/*
  2304	 * Try to allocate slabobj_ext array from unused space.
  2305	 * This function must be called on a freshly allocated slab to prevent
  2306	 * concurrency problems.
  2307	 */
  2308	static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab)
  2309	{
  2310		void *addr;
  2311		unsigned long obj_exts;
  2312	
  2313		if (!need_slab_obj_exts(s))
  2314			return;
  2315	
  2316		if (obj_exts_fit_within_slab_leftover(s, slab)) {
  2317			addr = slab_address(slab) + obj_exts_offset_in_slab(s, slab);
  2318			addr = kasan_reset_tag(addr);
  2319			obj_exts = (unsigned long)addr;
  2320	
  2321			get_slab_obj_exts(obj_exts);
  2322			memset(addr, 0, obj_exts_size_in_slab(slab));
  2323			put_slab_obj_exts(obj_exts);
  2324	
  2325			if (IS_ENABLED(CONFIG_MEMCG))
> 2326				obj_exts |= MEMCG_DATA_OBJEXTS;
  2327			slab->obj_exts = obj_exts;
  2328			slab_set_stride(slab, sizeof(struct slabobj_ext));
  2329		}
  2330	}
  2331	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki