Re: [PATCH v7 6/6] fs/dcache: Allow deconfiguration of negative dentry code to reduce kernel size

From: kbuild test robot
Date: Mon Jul 16 2018 - 21:15:12 EST

Hi Waiman,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.18-rc4]
[cannot apply to next-20180713]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Waiman-Long/fs-dcache-Track-report-number-of-negative-dentries/20180714-161258
config: h8300-h8300h-sim_defconfig (attached as .config)
compiler: h8300-linux-gcc (GCC) 8.1.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
GCC_VERSION=8.1.0 make.cross ARCH=h8300
:::::: branch date: 65 minutes ago
:::::: commit date: 65 minutes ago

All errors (new ones prefixed by >>):

fs/dcache.c: In function 'neg_dentry_inc_slowpath':
>> fs/dcache.c:374:8: error: implicit declaration of function 'get_nr_dentry_neg'; did you mean 'get_nr_dirty_inodes'? [-Werror=implicit-function-declaration]
cnt = get_nr_dentry_neg();
^~~~~~~~~~~~~~~~~
get_nr_dirty_inodes
cc1: some warnings being treated as errors

# https://github.com/0day-ci/linux/commit/ca68ee513a450445b269248c2859302c8931a294
git remote add linux-review https://github.com/0day-ci/linux
git remote update linux-review
git checkout ca68ee513a450445b269248c2859302c8931a294
vim +374 fs/dcache.c

bcc9ba8b Waiman Long 2018-07-12 311
2ccdd02c Waiman Long 2018-07-12 312 static noinline int neg_dentry_inc_slowpath(struct dentry *dentry)
bcc9ba8b Waiman Long 2018-07-12 313 {
bcc9ba8b Waiman Long 2018-07-12 314 long cnt = 0, *pcnt;
2aa8bf46 Waiman Long 2018-07-12 315 unsigned long current_time;
bcc9ba8b Waiman Long 2018-07-12 316
bcc9ba8b Waiman Long 2018-07-12 317 /*
bcc9ba8b Waiman Long 2018-07-12 318 * Try to move some negative dentry quota from the global free
bcc9ba8b Waiman Long 2018-07-12 319 * pool to the percpu count to allow more negative dentries to
bcc9ba8b Waiman Long 2018-07-12 320 * be added to the LRU.
bcc9ba8b Waiman Long 2018-07-12 321 */
bcc9ba8b Waiman Long 2018-07-12 322 pcnt = get_cpu_ptr(&nr_dentry_neg);
bcc9ba8b Waiman Long 2018-07-12 323 if ((READ_ONCE(ndblk.nfree) > 0) &&
bcc9ba8b Waiman Long 2018-07-12 324 (*pcnt > neg_dentry_percpu_limit)) {
bcc9ba8b Waiman Long 2018-07-12 325 cnt = __neg_dentry_nfree_dec(*pcnt - neg_dentry_percpu_limit);
bcc9ba8b Waiman Long 2018-07-12 326 *pcnt -= cnt;
bcc9ba8b Waiman Long 2018-07-12 327 }
bcc9ba8b Waiman Long 2018-07-12 328 put_cpu_ptr(&nr_dentry_neg);
bcc9ba8b Waiman Long 2018-07-12 329
2aa8bf46 Waiman Long 2018-07-12 330 if (cnt)
2aa8bf46 Waiman Long 2018-07-12 331 goto out;
2aa8bf46 Waiman Long 2018-07-12 332
bcc9ba8b Waiman Long 2018-07-12 333 /*
2ccdd02c Waiman Long 2018-07-12 334 * Kill the dentry by setting the DCACHE_KILL_NEGATIVE flag and
2ccdd02c Waiman Long 2018-07-12 335 * dec the negative dentry count if the enforcing option is on.
2ccdd02c Waiman Long 2018-07-12 336 */
2ccdd02c Waiman Long 2018-07-12 337 if (neg_dentry_enforce) {
2ccdd02c Waiman Long 2018-07-12 338 dentry->d_flags |= DCACHE_KILL_NEGATIVE;
2ccdd02c Waiman Long 2018-07-12 339 this_cpu_dec(nr_dentry_neg);
2ccdd02c Waiman Long 2018-07-12 340
2ccdd02c Waiman Long 2018-07-12 341 /*
2ccdd02c Waiman Long 2018-07-12 342 * When the dentry is not put into the LRU, we
2ccdd02c Waiman Long 2018-07-12 343 * need to keep the reference count to 1 to
2ccdd02c Waiman Long 2018-07-12 344 * avoid problem when killing it.
2ccdd02c Waiman Long 2018-07-12 345 */
2ccdd02c Waiman Long 2018-07-12 346 WARN_ON_ONCE(dentry->d_lockref.count);
2ccdd02c Waiman Long 2018-07-12 347 dentry->d_lockref.count = 1;
2ccdd02c Waiman Long 2018-07-12 348 return -1; /* Kill the dentry now */
2ccdd02c Waiman Long 2018-07-12 349 }
2ccdd02c Waiman Long 2018-07-12 350
2ccdd02c Waiman Long 2018-07-12 351 /*
2aa8bf46 Waiman Long 2018-07-12 352 * Put out a warning every minute or so if there are just too many
2aa8bf46 Waiman Long 2018-07-12 353 * negative dentries.
bcc9ba8b Waiman Long 2018-07-12 354 */
2aa8bf46 Waiman Long 2018-07-12 355 current_time = jiffies;
bcc9ba8b Waiman Long 2018-07-12 356
2aa8bf46 Waiman Long 2018-07-12 357 if (current_time < ndblk.warn_jiffies + NEG_WARN_PERIOD)
2aa8bf46 Waiman Long 2018-07-12 358 goto out;
2aa8bf46 Waiman Long 2018-07-12 359 /*
2aa8bf46 Waiman Long 2018-07-12 360 * Update the time in ndblk.warn_jiffies and print a warning
2aa8bf46 Waiman Long 2018-07-12 361 * if time update is successful.
2aa8bf46 Waiman Long 2018-07-12 362 */
2aa8bf46 Waiman Long 2018-07-12 363 raw_spin_lock(&ndblk.nfree_lock);
2aa8bf46 Waiman Long 2018-07-12 364 if (current_time < ndblk.warn_jiffies + NEG_WARN_PERIOD) {
2aa8bf46 Waiman Long 2018-07-12 365 raw_spin_unlock(&ndblk.nfree_lock);
2aa8bf46 Waiman Long 2018-07-12 366 goto out;
2aa8bf46 Waiman Long 2018-07-12 367 }
2aa8bf46 Waiman Long 2018-07-12 368 ndblk.warn_jiffies = current_time;
2aa8bf46 Waiman Long 2018-07-12 369 raw_spin_unlock(&ndblk.nfree_lock);
2aa8bf46 Waiman Long 2018-07-12 370
2aa8bf46 Waiman Long 2018-07-12 371 /*
2aa8bf46 Waiman Long 2018-07-12 372 * Get the current negative dentry count & print a warning.
2aa8bf46 Waiman Long 2018-07-12 373 */
2aa8bf46 Waiman Long 2018-07-12 @374 cnt = get_nr_dentry_neg();
2aa8bf46 Waiman Long 2018-07-12 375 pr_warn("Warning: Too many negative dentries (%ld). "
2ccdd02c Waiman Long 2018-07-12 376 "This warning can be disabled by writing 0 to \"fs/neg-dentry-limit\", increasing the limit or writing 1 to \"fs/neg-dentry-enforce\".\n",
2aa8bf46 Waiman Long 2018-07-12 377 cnt);
2aa8bf46 Waiman Long 2018-07-12 378 out:
2ccdd02c Waiman Long 2018-07-12 379 return 0;
bcc9ba8b Waiman Long 2018-07-12 380 }
bcc9ba8b Waiman Long 2018-07-12 381

:::::: The code at line 374 was first introduced by commit
:::::: 2aa8bf4658af0dbc07ae9ea07d04937a347e3ef4 fs/dcache: Print negative dentry warning every min until turned off by user

:::::: TO: Waiman Long <longman@xxxxxxxxxx>
:::::: CC: 0day robot <lkp@xxxxxxxxx>

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