Re: [RFC PATCH 3/3] memcg-v1: remove memcg move locking code

[kernel test robot <lkp@intel.com>]

Hi Shakeel,

[This is a private test report for your RFC patch.]
kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on next-20241025]
[cannot apply to tj-cgroup/for-next brauner-vfs/vfs.all linus/master v6.12-rc4]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Shakeel-Butt/memcg-v1-fully-deprecate-move_charge_at_immigrate/20241025-132623
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20241024065712.1274481-4-shakeel.butt%40linux.dev
patch subject: [RFC PATCH 3/3] memcg-v1: remove memcg move locking code
config: arc-randconfig-002-20241027 (https://download.01.org/0day-ci/archive/20241027/202410271408.tc8QGSge-lkp@intel.com/config)
compiler: arceb-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241027/202410271408.tc8QGSge-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410271408.tc8QGSge-lkp@intel.com/

All warnings (new ones prefixed by >>):

   mm/vmscan.c: In function 'walk_mm':
>> mm/vmscan.c:3652:28: warning: unused variable 'memcg' [-Wunused-variable]
    3652 |         struct mem_cgroup *memcg = lruvec_memcg(lruvec);
         |                            ^~~~~


vim +/memcg +3652 mm/vmscan.c

bd74fdaea14602 Yu Zhao            2022-09-18  3641  
2d823764fafa65 Kinsey Ho          2024-02-14  3642  static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
bd74fdaea14602 Yu Zhao            2022-09-18  3643  {
bd74fdaea14602 Yu Zhao            2022-09-18  3644  	static const struct mm_walk_ops mm_walk_ops = {
bd74fdaea14602 Yu Zhao            2022-09-18  3645  		.test_walk = should_skip_vma,
bd74fdaea14602 Yu Zhao            2022-09-18  3646  		.p4d_entry = walk_pud_range,
49b0638502da09 Suren Baghdasaryan 2023-08-04  3647  		.walk_lock = PGWALK_RDLOCK,
bd74fdaea14602 Yu Zhao            2022-09-18  3648  	};
bd74fdaea14602 Yu Zhao            2022-09-18  3649  
bd74fdaea14602 Yu Zhao            2022-09-18  3650  	int err;
2d823764fafa65 Kinsey Ho          2024-02-14  3651  	struct lruvec *lruvec = walk->lruvec;
bd74fdaea14602 Yu Zhao            2022-09-18 @3652  	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
bd74fdaea14602 Yu Zhao            2022-09-18  3653  
bd74fdaea14602 Yu Zhao            2022-09-18  3654  	walk->next_addr = FIRST_USER_ADDRESS;
bd74fdaea14602 Yu Zhao            2022-09-18  3655  
bd74fdaea14602 Yu Zhao            2022-09-18  3656  	do {
7f63cf2d9b9bbe Kalesh Singh       2023-04-13  3657  		DEFINE_MAX_SEQ(lruvec);
7f63cf2d9b9bbe Kalesh Singh       2023-04-13  3658  
bd74fdaea14602 Yu Zhao            2022-09-18  3659  		err = -EBUSY;
bd74fdaea14602 Yu Zhao            2022-09-18  3660  
7f63cf2d9b9bbe Kalesh Singh       2023-04-13  3661  		/* another thread might have called inc_max_seq() */
cc25bbe10a86a7 Kinsey Ho          2024-02-14  3662  		if (walk->seq != max_seq)
7f63cf2d9b9bbe Kalesh Singh       2023-04-13  3663  			break;
7f63cf2d9b9bbe Kalesh Singh       2023-04-13  3664  
bd74fdaea14602 Yu Zhao            2022-09-18  3665  		/* the caller might be holding the lock for write */
bd74fdaea14602 Yu Zhao            2022-09-18  3666  		if (mmap_read_trylock(mm)) {
bd74fdaea14602 Yu Zhao            2022-09-18  3667  			err = walk_page_range(mm, walk->next_addr, ULONG_MAX, &mm_walk_ops, walk);
bd74fdaea14602 Yu Zhao            2022-09-18  3668  
bd74fdaea14602 Yu Zhao            2022-09-18  3669  			mmap_read_unlock(mm);
bd74fdaea14602 Yu Zhao            2022-09-18  3670  		}
bd74fdaea14602 Yu Zhao            2022-09-18  3671  
bd74fdaea14602 Yu Zhao            2022-09-18  3672  		if (walk->batched) {
bd74fdaea14602 Yu Zhao            2022-09-18  3673  			spin_lock_irq(&lruvec->lru_lock);
2d823764fafa65 Kinsey Ho          2024-02-14  3674  			reset_batch_size(walk);
bd74fdaea14602 Yu Zhao            2022-09-18  3675  			spin_unlock_irq(&lruvec->lru_lock);
bd74fdaea14602 Yu Zhao            2022-09-18  3676  		}
bd74fdaea14602 Yu Zhao            2022-09-18  3677  
bd74fdaea14602 Yu Zhao            2022-09-18  3678  		cond_resched();
bd74fdaea14602 Yu Zhao            2022-09-18  3679  	} while (err == -EAGAIN);
bd74fdaea14602 Yu Zhao            2022-09-18  3680  }
bd74fdaea14602 Yu Zhao            2022-09-18  3681  

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