Re: [PATCH WIP v1 17/20] mm/rmap_id: reduce atomic RMW operations when we are the exclusive writer

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

Hi David,

kernel test robot noticed the following build errors:

[auto build test ERROR on b85ea95d086471afb4ad062012a4d73cd328fa86]

url:    https://github.com/intel-lab-lkp/linux/commits/David-Hildenbrand/mm-rmap-factor-out-adding-folio-range-into-__folio_add_rmap_range/20231124-213038
base:   b85ea95d086471afb4ad062012a4d73cd328fa86
patch link:    https://lore.kernel.org/r/20231124132626.235350-18-david%40redhat.com
patch subject: [PATCH WIP v1 17/20] mm/rmap_id: reduce atomic RMW operations when we are the exclusive writer
config: riscv-randconfig-r071-20231125 (https://download.01.org/0day-ci/archive/20231125/202311250405.RJLLR5GA-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/20231125/202311250405.RJLLR5GA-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/202311250405.RJLLR5GA-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from mm/filemap.c:40:
>> include/linux/rmap.h:304:3: error: call to undeclared function 'prefetchw'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     304 |                 prefetchw(&folio->_rmap_val0);
         |                 ^
   1 error generated.
--
   In file included from mm/mremap.c:15:
   In file included from include/linux/ksm.h:14:
>> include/linux/rmap.h:304:3: error: call to undeclared function 'prefetchw'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     304 |                 prefetchw(&folio->_rmap_val0);
         |                 ^
   In file included from mm/mremap.c:16:
   include/linux/mman.h:158:9: warning: division by zero is undefined [-Wdivision-by-zero]
     158 |                _calc_vm_trans(flags, MAP_SYNC,       VM_SYNC      ) |
         |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/mman.h:136:21: note: expanded from macro '_calc_vm_trans'
     136 |    : ((x) & (bit1)) / ((bit1) / (bit2))))
         |                     ^ ~~~~~~~~~~~~~~~~~
   1 warning and 1 error generated.


vim +/prefetchw +304 include/linux/rmap.h

   293	
   294	static inline bool __folio_write_large_rmap_begin(struct folio *folio)
   295	{
   296		bool exclusive;
   297	
   298		VM_WARN_ON_FOLIO(!folio_test_large_rmappable(folio), folio);
   299		VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
   300	
   301		exclusive = raw_write_atomic_seqcount_begin(&folio->_rmap_atomic_seqcount,
   302							    true);
   303		if (likely(exclusive)) {
 > 304			prefetchw(&folio->_rmap_val0);
   305			if (unlikely(folio_order(folio) > RMAP_SUBID_4_MAX_ORDER))
   306				prefetchw(&folio->_rmap_val4);
   307		}
   308		return exclusive;
   309	}
   310	

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