Re: [PATCH v2] workingset: ensure memcg is valid for recency check

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

Hi Nhat,

kernel test robot noticed the following build errors:

[auto build test ERROR on linus/master]
[also build test ERROR on v6.5-rc6 next-20230817]
[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/Nhat-Pham/workingset-ensure-memcg-is-valid-for-recency-check/20230818-030311
base:   linus/master
patch link:    https://lore.kernel.org/r/20230817190126.3155299-1-nphamcs%40gmail.com
patch subject: [PATCH v2] workingset: ensure memcg is valid for recency check
config: loongarch-allnoconfig (https://download.01.org/0day-ci/archive/20230818/202308181116.FsJVPmJZ-lkp@intel.com/config)
compiler: loongarch64-linux-gcc (GCC) 12.3.0
reproduce: (https://download.01.org/0day-ci/archive/20230818/202308181116.FsJVPmJZ-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/202308181116.FsJVPmJZ-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/workingset.c: In function 'unpack_shadow':
>> mm/workingset.c:245:22: error: implicit declaration of function 'css_tryget'; did you mean 'wb_tryget'? [-Werror=implicit-function-declaration]
     245 |         if (memcg && css_tryget(&memcg->css))
         |                      ^~~~~~~~~~
         |                      wb_tryget
   mm/workingset.c:245:39: error: invalid use of undefined type 'struct mem_cgroup'
     245 |         if (memcg && css_tryget(&memcg->css))
         |                                       ^~
   cc1: some warnings being treated as errors


vim +245 mm/workingset.c

   208	
   209	/*
   210	 * Unpacks the stored fields of a shadow entry into the given pointers.
   211	 *
   212	 * The memcg pointer is only populated if the memcg recorded in the shadow
   213	 * entry is valid. In this case, a reference to the memcg will be acquired,
   214	 * and a corresponding mem_cgroup_put() will be needed when we no longer
   215	 * need the memcg.
   216	 */
   217	static void unpack_shadow(void *shadow, struct mem_cgroup **memcgp,
   218				pg_data_t **pgdat, unsigned long *evictionp, bool *workingsetp)
   219	{
   220		unsigned long entry = xa_to_value(shadow);
   221		struct mem_cgroup *memcg;
   222		int memcgid, nid;
   223		bool workingset;
   224	
   225		workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
   226		entry >>= WORKINGSET_SHIFT;
   227		nid = entry & ((1UL << NODES_SHIFT) - 1);
   228		entry >>= NODES_SHIFT;
   229		memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
   230		entry >>= MEM_CGROUP_ID_SHIFT;
   231	
   232		/*
   233		 * Look up the memcg associated with the stored ID. It might
   234		 * have been deleted since the folio's eviction.
   235		 *
   236		 * Note that in rare events the ID could have been recycled
   237		 * for a new cgroup that refaults a shared folio. This is
   238		 * impossible to tell from the available data. However, this
   239		 * should be a rare and limited disturbance, and activations
   240		 * are always speculative anyway. Ultimately, it's the aging
   241		 * algorithm's job to shake out the minimum access frequency
   242		 * for the active cache.
   243		 */
   244		memcg = mem_cgroup_from_id(memcgid);
 > 245		if (memcg && css_tryget(&memcg->css))
   246			*memcgp = memcg;
   247		else
   248			*memcgp = NULL;
   249	
   250		*pgdat = NODE_DATA(nid);
   251		*evictionp = entry;
   252		*workingsetp = workingset;
   253	}
   254	

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