Re: [PATCH v3 4/4] btrfs: avoid allocating unnecessary page pointers

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

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Hi Qu,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kdave/for-next]
[also build test WARNING on next-20200826]
[cannot apply to btrfs/next v5.9-rc2]
[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]

url:    https://github.com/0day-ci/linux/commits/Qu-Wenruo/btrfs-basic-refactor-of-btrfs_buffered_write/20200825-135114
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git for-next
config: riscv-randconfig-r033-20200826 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 7cfcecece0e0430937cf529ce74d3a071a4dedc6)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=riscv 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> fs/btrfs/file.c:1571:13: warning: comparison of distinct pointer types ('typeof (nr_pages) *' (aka 'int *') and 'typeof (65536 / ((1UL) << (12))) *' (aka 'unsigned long *')) [-Wcompare-distinct-pointer-types]
           nr_pages = min(nr_pages, SZ_64K / PAGE_SIZE);
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/kernel.h:883:19: note: expanded from macro 'min'
   #define min(x, y)       __careful_cmp(x, y, <)
                           ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/kernel.h:874:24: note: expanded from macro '__careful_cmp'
           __builtin_choose_expr(__safe_cmp(x, y), \
                                 ^~~~~~~~~~~~~~~~
   include/linux/kernel.h:864:4: note: expanded from macro '__safe_cmp'
                   (__typecheck(x, y) && __no_side_effects(x, y))
                    ^~~~~~~~~~~~~~~~~
   include/linux/kernel.h:850:29: note: expanded from macro '__typecheck'
                   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                              ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
   1 warning generated.

# https://github.com/0day-ci/linux/commit/a73ab37ebab960522a0b353a6f20c8094ab911c5
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Qu-Wenruo/btrfs-basic-refactor-of-btrfs_buffered_write/20200825-135114
git checkout a73ab37ebab960522a0b353a6f20c8094ab911c5
vim +1571 fs/btrfs/file.c

  1548	
  1549	/* Helper to get how many pages we should alloc for the batch */
  1550	static int calc_nr_pages(loff_t pos, struct iov_iter *iov)
  1551	{
  1552		int nr_pages;
  1553	
  1554		/*
  1555		 * Try to cover the full iov range, as btrfs metadata/data reserve
  1556		 * and release can be pretty slow, thus the more pages we process in
  1557		 * one batch the better.
  1558		 */
  1559		nr_pages = (round_up(pos + iov_iter_count(iov), PAGE_SIZE) -
  1560			    round_down(pos, PAGE_SIZE)) / PAGE_SIZE;
  1561	
  1562		nr_pages = min(nr_pages, current->nr_dirtied_pause -
  1563					 current->nr_dirtied);
  1564	
  1565		/*
  1566		 * Limit the batch to 64K, too large batch may lead to higher memory
  1567		 * pressure and increase the possibility of short-copy.
  1568		 * With more and more short-copy, the benefit of batch copy would be
  1569		 * hugely reduced, as we will fall back to page-by-page copy.
  1570		 */
> 1571		nr_pages = min(nr_pages, SZ_64K / PAGE_SIZE);
  1572		return nr_pages;
  1573	}
  1574	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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