Re: [PATCH] dcache: add fs.dentry-limit sysctl with negative-first reaper

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

Hi Horst,

kernel test robot noticed the following build errors:

[auto build test ERROR on 5d6919055dec134de3c40167a490f33c74c12581]

url:    https://github.com/intel-lab-lkp/linux/commits/Horst-Birthelmer/dcache-add-fs-dentry-limit-sysctl-with-negative-first-reaper/20260515-154600
base:   5d6919055dec134de3c40167a490f33c74c12581
patch link:    https://lore.kernel.org/r/20260514-limit-dentries-cache-v1-1-431b9eb0c530%40ddn.com
patch subject: [PATCH] dcache: add fs.dentry-limit sysctl with negative-first reaper
config: s390-randconfig-002-20260515 (https://download.01.org/0day-ci/archive/20260515/202605152329.WHnEvZt7-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 5bac06718f502014fade905512f1d26d578a18f3)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260515/202605152329.WHnEvZt7-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/202605152329.WHnEvZt7-lkp@intel.com/

All errors (new ones prefixed by >>):

>> fs/dcache.c:1474:7: error: call to undeclared function 'get_nr_dentry'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    1474 |         nr = get_nr_dentry();
         |              ^
   fs/dcache.c:1474:7: note: did you mean 'retain_dentry'?
   fs/dcache.c:835:20: note: 'retain_dentry' declared here
     835 | static inline bool retain_dentry(struct dentry *dentry, bool locked)
         |                    ^
   fs/dcache.c:1519:6: error: call to undeclared function 'get_nr_dentry'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    1519 |         if (get_nr_dentry() <= (long)limit)
         |             ^
   2 errors generated.


vim +/get_nr_dentry +1474 fs/dcache.c

  1463	
  1464	static void dentry_limit_worker_fn(struct work_struct *work)
  1465	{
  1466		struct dentry_limit_ctx ctx;
  1467		unsigned long limit = READ_ONCE(sysctl_dentry_limit);
  1468		unsigned int ms;
  1469		long nr;
  1470	
  1471		if (!limit)
  1472			return;
  1473	
> 1474		nr = get_nr_dentry();
  1475		if (nr <= (long)limit)
  1476			return;
  1477	
  1478		ctx.over = nr - (long)limit;
  1479	
  1480		/* Phase 1: drain negative dentries across every superblock. */
  1481		ctx.isolate = dentry_lru_isolate_negative;
  1482		iterate_supers(dentry_limit_prune_sb, &ctx);
  1483	
  1484		/* Phase 2: still over? Apply the ordinary LRU policy. */
  1485		if (ctx.over > 0) {
  1486			ctx.isolate = dentry_lru_isolate;
  1487			iterate_supers(dentry_limit_prune_sb, &ctx);
  1488		}
  1489	
  1490		/*
  1491		 * Re-arm while still above the limit. Re-read the sysctls in
  1492		 * case the admin raised the cap or disabled the feature during
  1493		 * the walk.
  1494		 */
  1495		limit = READ_ONCE(sysctl_dentry_limit);
  1496		if (!limit || get_nr_dentry() <= (long)limit)
  1497			return;
  1498	
  1499		ms = READ_ONCE(sysctl_dentry_limit_interval_ms);
  1500		queue_delayed_work(system_unbound_wq, &dentry_limit_work,
  1501				   msecs_to_jiffies(ms));
  1502	}
  1503	

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