Re: [PATCH v3 1/2] mm/vmscan: Skip memcg with !usage in shrink_node_memcgs()

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

Hi Waiman,

kernel test robot noticed the following build errors:

[auto build test ERROR on tj-cgroup/for-next]
[also build test ERROR on akpm-mm/mm-everything linus/master v6.14 next-20250404]
[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/Waiman-Long/mm-vmscan-Skip-memcg-with-usage-in-shrink_node_memcgs/20250406-104208
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20250406024010.1177927-2-longman%40redhat.com
patch subject: [PATCH v3 1/2] mm/vmscan: Skip memcg with !usage in shrink_node_memcgs()
config: arc-randconfig-002-20250406 (https://download.01.org/0day-ci/archive/20250406/202504061257.GMkEJUOs-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 11.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250406/202504061257.GMkEJUOs-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/202504061257.GMkEJUOs-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/vmscan.c: In function 'shrink_node_memcgs':
>> mm/vmscan.c:5929:46: error: invalid use of undefined type 'struct mem_cgroup'
    5929 |                 if (!page_counter_read(&memcg->memory))
         |                                              ^~


vim +5929 mm/vmscan.c

  5890	
  5891	static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
  5892	{
  5893		struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
  5894		struct mem_cgroup_reclaim_cookie reclaim = {
  5895			.pgdat = pgdat,
  5896		};
  5897		struct mem_cgroup_reclaim_cookie *partial = &reclaim;
  5898		struct mem_cgroup *memcg;
  5899	
  5900		/*
  5901		 * In most cases, direct reclaimers can do partial walks
  5902		 * through the cgroup tree, using an iterator state that
  5903		 * persists across invocations. This strikes a balance between
  5904		 * fairness and allocation latency.
  5905		 *
  5906		 * For kswapd, reliable forward progress is more important
  5907		 * than a quick return to idle. Always do full walks.
  5908		 */
  5909		if (current_is_kswapd() || sc->memcg_full_walk)
  5910			partial = NULL;
  5911	
  5912		memcg = mem_cgroup_iter(target_memcg, NULL, partial);
  5913		do {
  5914			struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
  5915			unsigned long reclaimed;
  5916			unsigned long scanned;
  5917	
  5918			/*
  5919			 * This loop can become CPU-bound when target memcgs
  5920			 * aren't eligible for reclaim - either because they
  5921			 * don't have any reclaimable pages, or because their
  5922			 * memory is explicitly protected. Avoid soft lockups.
  5923			 */
  5924			cond_resched();
  5925	
  5926			mem_cgroup_calculate_protection(target_memcg, memcg);
  5927	
  5928			/* Skip memcg with no usage */
> 5929			if (!page_counter_read(&memcg->memory))
  5930				continue;
  5931	
  5932			if (mem_cgroup_below_min(target_memcg, memcg)) {
  5933				/*
  5934				 * Hard protection.
  5935				 * If there is no reclaimable memory, OOM.
  5936				 */
  5937				continue;
  5938			} else if (mem_cgroup_below_low(target_memcg, memcg)) {
  5939				/*
  5940				 * Soft protection.
  5941				 * Respect the protection only as long as
  5942				 * there is an unprotected supply
  5943				 * of reclaimable memory from other cgroups.
  5944				 */
  5945				if (!sc->memcg_low_reclaim) {
  5946					sc->memcg_low_skipped = 1;
  5947					continue;
  5948				}
  5949				memcg_memory_event(memcg, MEMCG_LOW);
  5950			}
  5951	
  5952			reclaimed = sc->nr_reclaimed;
  5953			scanned = sc->nr_scanned;
  5954	
  5955			shrink_lruvec(lruvec, sc);
  5956	
  5957			shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
  5958				    sc->priority);
  5959	
  5960			/* Record the group's reclaim efficiency */
  5961			if (!sc->proactive)
  5962				vmpressure(sc->gfp_mask, memcg, false,
  5963					   sc->nr_scanned - scanned,
  5964					   sc->nr_reclaimed - reclaimed);
  5965	
  5966			/* If partial walks are allowed, bail once goal is reached */
  5967			if (partial && sc->nr_reclaimed >= sc->nr_to_reclaim) {
  5968				mem_cgroup_iter_break(target_memcg, memcg);
  5969				break;
  5970			}
  5971		} while ((memcg = mem_cgroup_iter(target_memcg, memcg, partial)));
  5972	}
  5973	

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