Re: [PATCH V2 2/2] block: try to make aligned bio in case of big chunk IO

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

Hi Ming,

kernel test robot noticed the following build warnings:

[auto build test WARNING on axboe-block/for-next]
[also build test WARNING on linus/master v6.6 next-20231109]
[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/Ming-Lei/block-don-t-call-into-iov_iter_revert-if-nothing-is-left/20231109-190100
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/20231109082827.2276696-3-ming.lei%40redhat.com
patch subject: [PATCH V2 2/2] block: try to make aligned bio in case of big chunk IO
config: arm-davinci_all_defconfig (https://download.01.org/0day-ci/archive/20231110/202311100354.HYfqOQ7o-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231110/202311100354.HYfqOQ7o-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/202311100354.HYfqOQ7o-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> block/bio.c:1228:21: warning: variable 'size' is uninitialized when used here [-Wuninitialized]
    1228 |                 return UINT_MAX - size;
         |                                   ^~~~
   block/bio.c:1221:19: note: initialize the variable 'size' to silence this warning
    1221 |         unsigned int size, predicted_space, max_bytes;
         |                          ^
         |                           = 0
   1 warning generated.

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for PINCTRL_SINGLE
   Depends on [n]: PINCTRL [=n] && OF [=y] && HAS_IOMEM [=y]
   Selected by [y]:
   - ARCH_DAVINCI [=y] && ARCH_MULTI_V5 [=y] && CPU_LITTLE_ENDIAN [=y]


vim +/size +1228 block/bio.c

  1212	
  1213	/*
  1214	 * Figure out max_size hint of iov_iter_extract_pages() for minimizing
  1215	 * bio & iov iter revert so that bio can be aligned with max io size.
  1216	 */
  1217	static unsigned int bio_get_buffer_size_hint(const struct bio *bio,
  1218			unsigned int left)
  1219	{
  1220		unsigned int nr_bvecs = bio->bi_max_vecs - bio->bi_vcnt;
  1221		unsigned int size, predicted_space, max_bytes;
  1222		unsigned int space = nr_bvecs << PAGE_SHIFT;
  1223		unsigned int align_deviation;
  1224	
  1225		/* If we have enough space really, just try to get all pages */
  1226		if (!bio->bi_bdev || nr_bvecs >= (bio->bi_max_vecs / 4) ||
  1227				!bio->bi_vcnt || left <= space)
> 1228			return UINT_MAX - size;
  1229	
  1230		max_bytes = bdev_max_io_bytes(bio->bi_bdev);
  1231		size = bio->bi_iter.bi_size;
  1232	
  1233		/*
  1234		 * One bvec can hold physically continuous page frames with
  1235		 * multipage bvec and bytes in these pages can be pretty big, so
  1236		 * predict the available space by averaging bytes on all bvecs
  1237		 */
  1238		predicted_space = size * nr_bvecs / bio->bi_vcnt;
  1239		/*
  1240		 * If predicted space is bigger than max io bytes and at least two
  1241		 * vectors left, ask for all pages
  1242		 */
  1243		if (predicted_space > max_bytes && nr_bvecs > 2)
  1244			return UINT_MAX - size;
  1245	
  1246		/*
  1247		 * This bio is close to be full, and stop to add pages if it is
  1248		 * basically aligned, otherwise just get & add pages if the bio
  1249		 * can be kept as aligned, so that we can minimize bio & iov iter
  1250		 * revert
  1251		 */
  1252		align_deviation = max_t(unsigned int, 16U * 1024, max_bytes / 16);
  1253		if ((size & (max_bytes - 1)) > align_deviation) {
  1254			unsigned aligned_bytes = max_bytes - (size & (max_bytes - 1));
  1255	
  1256			/* try to keep bio aligned if we have enough data and space */
  1257			if (aligned_bytes <= left && aligned_bytes <= predicted_space)
  1258				return aligned_bytes;
  1259		}
  1260	
  1261		return 0;
  1262	}
  1263	

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