Re: [PATCH v2] Increase page and bit waitqueue hash size

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

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Hi Nicholas,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linux/master]
[also build test WARNING on linus/master hnaz-linux-mm/master v5.12-rc3 next-20210317]
[cannot apply to tip/sched/core]
[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/Nicholas-Piggin/Increase-page-and-bit-waitqueue-hash-size/20210317-155619
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a74e6a014c9d4d4161061f770c9b4f98372ac778
config: x86_64-randconfig-a015-20210317 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 8ef111222a3dd12a9175f69c3bff598c46e8bdf7)
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 x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://github.com/0day-ci/linux/commit/d741b0903849631440ae34fb070178e9743c6928
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Nicholas-Piggin/Increase-page-and-bit-waitqueue-hash-size/20210317-155619
        git checkout d741b0903849631440ae34fb070178e9743c6928
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 

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 >>):

>> mm/filemap.c:997:42: warning: variable length arrays are a C99 feature [-Wvla-extension]
   static wait_queue_head_t page_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
                                            ^~~~~~~~~~~~~~~~~~~~
   mm/filemap.c:994:30: note: expanded from macro 'PAGE_WAIT_TABLE_SIZE'
   #define PAGE_WAIT_TABLE_SIZE (1 << page_wait_table_bits)
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/filemap.c:1018:8: error: passing 'const unsigned int *' to parameter of type 'unsigned int *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
                                                           &page_wait_table_bits,
                                                           ^~~~~~~~~~~~~~~~~~~~~
   include/linux/memblock.h:579:24: note: passing argument to parameter '_hash_shift' here
                                        unsigned int *_hash_shift,
                                                      ^
   mm/filemap.c:1013:19: error: array type 'wait_queue_head_t [16]' is not assignable
                   page_wait_table = alloc_large_system_hash("page waitqueue hash",
                   ~~~~~~~~~~~~~~~ ^
   1 warning and 2 errors generated.
--
>> kernel/sched/wait_bit.c:11:41: warning: variable length arrays are a C99 feature [-Wvla-extension]
   static wait_queue_head_t bit_wait_table[BIT_WAIT_TABLE_SIZE] __cacheline_aligned;
                                           ^~~~~~~~~~~~~~~~~~~
   kernel/sched/wait_bit.c:8:29: note: expanded from macro 'BIT_WAIT_TABLE_SIZE'
   #define BIT_WAIT_TABLE_SIZE (1 << bit_wait_table_bits)
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~
   kernel/sched/wait_bit.c:260:8: error: passing 'const unsigned int *' to parameter of type 'unsigned int *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
                                                           &bit_wait_table_bits,
                                                           ^~~~~~~~~~~~~~~~~~~~
   include/linux/memblock.h:579:24: note: passing argument to parameter '_hash_shift' here
                                        unsigned int *_hash_shift,
                                                      ^
   kernel/sched/wait_bit.c:255:18: error: array type 'wait_queue_head_t [8]' is not assignable
                   bit_wait_table = alloc_large_system_hash("bit waitqueue hash",
                   ~~~~~~~~~~~~~~ ^
   1 warning and 2 errors generated.


vim +997 mm/filemap.c

44110fe385af23 Paul Jackson    2006-03-24   983  
^1da177e4c3f41 Linus Torvalds  2005-04-16   984  /*
^1da177e4c3f41 Linus Torvalds  2005-04-16   985   * In order to wait for pages to become available there must be
^1da177e4c3f41 Linus Torvalds  2005-04-16   986   * waitqueues associated with pages. By using a hash table of
^1da177e4c3f41 Linus Torvalds  2005-04-16   987   * waitqueues where the bucket discipline is to maintain all
^1da177e4c3f41 Linus Torvalds  2005-04-16   988   * waiters on the same queue and wake all when any of the pages
^1da177e4c3f41 Linus Torvalds  2005-04-16   989   * become available, and for the woken contexts to check to be
^1da177e4c3f41 Linus Torvalds  2005-04-16   990   * sure the appropriate page became available, this saves space
^1da177e4c3f41 Linus Torvalds  2005-04-16   991   * at a cost of "thundering herd" phenomena during rare hash
^1da177e4c3f41 Linus Torvalds  2005-04-16   992   * collisions.
^1da177e4c3f41 Linus Torvalds  2005-04-16   993   */
d741b090384963 Nicholas Piggin 2021-03-17   994  #define PAGE_WAIT_TABLE_SIZE (1 << page_wait_table_bits)
d741b090384963 Nicholas Piggin 2021-03-17   995  #if CONFIG_BASE_SMALL
d741b090384963 Nicholas Piggin 2021-03-17   996  static const unsigned int page_wait_table_bits = 4;
62906027091f1d Nicholas Piggin 2016-12-25  @997  static wait_queue_head_t page_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
d741b090384963 Nicholas Piggin 2021-03-17   998  #else
d741b090384963 Nicholas Piggin 2021-03-17   999  static unsigned int page_wait_table_bits __ro_after_init;
d741b090384963 Nicholas Piggin 2021-03-17  1000  static wait_queue_head_t *page_wait_table __ro_after_init;
d741b090384963 Nicholas Piggin 2021-03-17  1001  #endif
62906027091f1d Nicholas Piggin 2016-12-25  1002  

---
0-DAY CI Kernel Test Service, Intel Corporation
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