Re: [PATCH -next 2/2] memcg: remove mem_cgroup_size()

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

Hi Chen,

kernel test robot noticed the following build errors:

[auto build test ERROR on next-20251209]

url:    https://github.com/intel-lab-lkp/linux/commits/Chen-Ridong/memcg-move-mem_cgroup_usage-memcontrol-v1-c/20251209-211854
base:   next-20251209
patch link:    https://lore.kernel.org/r/20251209130251.1988615-3-chenridong%40huaweicloud.com
patch subject: [PATCH -next 2/2] memcg: remove mem_cgroup_size()
config: i386-allnoconfig (https://download.01.org/0day-ci/archive/20251210/202512100924.LqJqXM7P-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251210/202512100924.LqJqXM7P-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/202512100924.LqJqXM7P-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/vmscan.c: In function 'apply_proportional_protection':
>> mm/vmscan.c:2488:63: error: invalid use of undefined type 'struct mem_cgroup'
    2488 |                 unsigned long usage = page_counter_read(&memcg->memory);
         |                                                               ^~


vim +2488 mm/vmscan.c

  2450	
  2451	static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
  2452			struct scan_control *sc, unsigned long scan)
  2453	{
  2454		unsigned long min, low;
  2455	
  2456		mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
  2457	
  2458		if (min || low) {
  2459			/*
  2460			 * Scale a cgroup's reclaim pressure by proportioning
  2461			 * its current usage to its memory.low or memory.min
  2462			 * setting.
  2463			 *
  2464			 * This is important, as otherwise scanning aggression
  2465			 * becomes extremely binary -- from nothing as we
  2466			 * approach the memory protection threshold, to totally
  2467			 * nominal as we exceed it.  This results in requiring
  2468			 * setting extremely liberal protection thresholds. It
  2469			 * also means we simply get no protection at all if we
  2470			 * set it too low, which is not ideal.
  2471			 *
  2472			 * If there is any protection in place, we reduce scan
  2473			 * pressure by how much of the total memory used is
  2474			 * within protection thresholds.
  2475			 *
  2476			 * There is one special case: in the first reclaim pass,
  2477			 * we skip over all groups that are within their low
  2478			 * protection. If that fails to reclaim enough pages to
  2479			 * satisfy the reclaim goal, we come back and override
  2480			 * the best-effort low protection. However, we still
  2481			 * ideally want to honor how well-behaved groups are in
  2482			 * that case instead of simply punishing them all
  2483			 * equally. As such, we reclaim them based on how much
  2484			 * memory they are using, reducing the scan pressure
  2485			 * again by how much of the total memory used is under
  2486			 * hard protection.
  2487			 */
> 2488			unsigned long usage = page_counter_read(&memcg->memory);
  2489			unsigned long protection;
  2490	
  2491			/* memory.low scaling, make sure we retry before OOM */
  2492			if (!sc->memcg_low_reclaim && low > min) {
  2493				protection = low;
  2494				sc->memcg_low_skipped = 1;
  2495			} else {
  2496				protection = min;
  2497			}
  2498	
  2499			/* Avoid TOCTOU with earlier protection check */
  2500			usage = max(usage, protection);
  2501	
  2502			scan -= scan * protection / (usage + 1);
  2503	
  2504			/*
  2505			 * Minimally target SWAP_CLUSTER_MAX pages to keep
  2506			 * reclaim moving forwards, avoiding decrementing
  2507			 * sc->priority further than desirable.
  2508			 */
  2509			scan = max(scan, SWAP_CLUSTER_MAX);
  2510		}
  2511		return scan;
  2512	}
  2513	

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