Re: [PATCH v5 1/2] btrfs: always uses root memcgroup for filemap_add_folio()

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

Hi Qu,

kernel test robot noticed the following build errors:

[auto build test ERROR on kdave/for-next]
[also build test ERROR on linus/master v6.10 next-20240719]
[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/Qu-Wenruo/btrfs-always-uses-root-memcgroup-for-filemap_add_folio/20240719-125131
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git for-next
patch link:    https://lore.kernel.org/r/d408a1b35307101e82a6845e26af4a122c8e5a25.1721363035.git.wqu%40suse.com
patch subject: [PATCH v5 1/2] btrfs: always uses root memcgroup for filemap_add_folio()
config: x86_64-buildonly-randconfig-002-20240719 (https://download.01.org/0day-ci/archive/20240719/202407192346.BjAEmrYl-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240719/202407192346.BjAEmrYl-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/202407192346.BjAEmrYl-lkp@intel.com/

All errors (new ones prefixed by >>):

>> fs/btrfs/extent_io.c:2992:31: error: use of undeclared identifier 'root_mem_cgroup'; did you mean 'parent_mem_cgroup'?
    2992 |         old_memcg = set_active_memcg(root_mem_cgroup);
         |                                      ^~~~~~~~~~~~~~~
         |                                      parent_mem_cgroup
   include/linux/memcontrol.h:1288:34: note: 'parent_mem_cgroup' declared here
    1288 | static inline struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
         |                                  ^
   1 error generated.


vim +2992 fs/btrfs/extent_io.c

  2971	
  2972		struct btrfs_fs_info *fs_info = eb->fs_info;
  2973		struct address_space *mapping = fs_info->btree_inode->i_mapping;
  2974		struct mem_cgroup *old_memcg;
  2975		const unsigned long index = eb->start >> PAGE_SHIFT;
  2976		struct folio *existing_folio = NULL;
  2977		int ret;
  2978	
  2979		ASSERT(found_eb_ret);
  2980	
  2981		/* Caller should ensure the folio exists. */
  2982		ASSERT(eb->folios[i]);
  2983	
  2984	retry:
  2985		/*
  2986		 * Btree inode is a btrfs internal inode, and not exposed to any
  2987		 * user.
  2988		 * Furthermore we do not want any cgroup limits on this inode.
  2989		 * So we always use root_mem_cgroup as our active memcg when attaching
  2990		 * the folios.
  2991		 */
> 2992		old_memcg = set_active_memcg(root_mem_cgroup);
  2993		ret = filemap_add_folio(mapping, eb->folios[i], index + i,
  2994					GFP_NOFS | __GFP_NOFAIL);
  2995		set_active_memcg(old_memcg);
  2996		if (!ret)
  2997			goto finish;
  2998	
  2999		existing_folio = filemap_lock_folio(mapping, index + i);
  3000		/* The page cache only exists for a very short time, just retry. */
  3001		if (IS_ERR(existing_folio)) {
  3002			existing_folio = NULL;
  3003			goto retry;
  3004		}
  3005	
  3006		/* For now, we should only have single-page folios for btree inode. */
  3007		ASSERT(folio_nr_pages(existing_folio) == 1);
  3008	
  3009		if (folio_size(existing_folio) != eb->folio_size) {
  3010			folio_unlock(existing_folio);
  3011			folio_put(existing_folio);
  3012			return -EAGAIN;
  3013		}
  3014	
  3015	finish:
  3016		spin_lock(&mapping->i_private_lock);
  3017		if (existing_folio && fs_info->nodesize < PAGE_SIZE) {
  3018			/* We're going to reuse the existing page, can drop our folio now. */
  3019			__free_page(folio_page(eb->folios[i], 0));
  3020			eb->folios[i] = existing_folio;
  3021		} else if (existing_folio) {
  3022			struct extent_buffer *existing_eb;
  3023	
  3024			existing_eb = grab_extent_buffer(fs_info,
  3025							 folio_page(existing_folio, 0));
  3026			if (existing_eb) {
  3027				/* The extent buffer still exists, we can use it directly. */
  3028				*found_eb_ret = existing_eb;
  3029				spin_unlock(&mapping->i_private_lock);
  3030				folio_unlock(existing_folio);
  3031				folio_put(existing_folio);
  3032				return 1;
  3033			}
  3034			/* The extent buffer no longer exists, we can reuse the folio. */
  3035			__free_page(folio_page(eb->folios[i], 0));
  3036			eb->folios[i] = existing_folio;
  3037		}
  3038		eb->folio_size = folio_size(eb->folios[i]);
  3039		eb->folio_shift = folio_shift(eb->folios[i]);
  3040		/* Should not fail, as we have preallocated the memory. */
  3041		ret = attach_extent_buffer_folio(eb, eb->folios[i], prealloc);
  3042		ASSERT(!ret);
  3043		/*
  3044		 * To inform we have an extra eb under allocation, so that
  3045		 * detach_extent_buffer_page() won't release the folio private when the
  3046		 * eb hasn't been inserted into radix tree yet.
  3047		 *
  3048		 * The ref will be decreased when the eb releases the page, in
  3049		 * detach_extent_buffer_page().  Thus needs no special handling in the
  3050		 * error path.
  3051		 */
  3052		btrfs_folio_inc_eb_refs(fs_info, eb->folios[i]);
  3053		spin_unlock(&mapping->i_private_lock);
  3054		return 0;
  3055	}
  3056	

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