Re: [akpm-mm:mm-unstable 36/283] mm/hugetlb.c:4753:18: warning: implicit conversion from 'unsigned long long' to 'unsigned long' changes value from 17179869184 to 0

[Nathan Chancellor <nathan@kernel.org>]

On Fri, Nov 14, 2025 at 02:46:06PM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> head:   1c571d1c4c7e042c3c313d1a2058a17848ccebac
> commit: 2f6ff71280ffddb27ad7174d24f573e2683870cd [36/283] mm: fix MAX_FOLIO_ORDER on powerpc configs with hugetlb
> config: powerpc-randconfig-002-20251114 (https://download.01.org/0day-ci/archive/20251114/202511141140.LrrRrtIv-lkp@intel.com/config)
> compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 0bba1e76581bad04e7d7f09f5115ae5e2989e0d9)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251114/202511141140.LrrRrtIv-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/202511141140.LrrRrtIv-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
...
> >> mm/util.c:1263:16: warning: implicit conversion from 'unsigned long long' to 'unsigned long' changes value from 17179869184 to 0 [-Wconstant-conversion]
>     1263 |         if (ps->idx < MAX_FOLIO_NR_PAGES) {
>          |                       ^~~~~~~~~~~~~~~~~~
>    include/linux/mm.h:2104:36: note: expanded from macro 'MAX_FOLIO_NR_PAGES'
>     2104 | #define MAX_FOLIO_NR_PAGES      (1UL << MAX_FOLIO_ORDER)
>          |                                         ^~~~~~~~~~~~~~~
>    include/linux/mm.h:2095:36: note: expanded from macro 'MAX_FOLIO_ORDER'
>     2095 | #define MAX_FOLIO_ORDER         get_order(SZ_16G)
>          |                                 ~~~~~~~~~ ^~~~~~
>    include/linux/sizes.h:56:19: note: expanded from macro 'SZ_16G'
>       56 | #define SZ_16G                          _AC(0x400000000, ULL)
>          |                                         ^~~~~~~~~~~~~~~~~~~~~
>    include/uapi/linux/const.h:21:18: note: expanded from macro '_AC'
>       21 | #define _AC(X,Y)        __AC(X,Y)
>          |                         ^~~~~~~~~
>    include/uapi/linux/const.h:20:20: note: expanded from macro '__AC'
>       20 | #define __AC(X,Y)       (X##Y)
>          |                          ^~~~
>    <scratch space>:39:1: note: expanded from here
>       39 | 0x400000000ULL
>          | ^~~~~~~~~~~~~~
>    1 warning generated.

For the record, this is not a clang specific warning, as it happens when
building the same configuration with GCC:

  In file included from include/vdso/const.h:5,
                   from include/vdso/bits.h:5,
                   from include/linux/bits.h:5,
                   from include/linux/ratelimit_types.h:5,
                   from include/linux/printk.h:9,
                   from include/asm-generic/bug.h:28,
                   from arch/powerpc/include/asm/bug.h:116,
                   from include/linux/bug.h:5,
                   from include/linux/mmdebug.h:5,
                   from include/linux/mm.h:6,
                   from mm/util.c:2:
  mm/util.c: In function 'snapshot_page':
  include/uapi/linux/const.h:20:25: warning: conversion from 'long long unsigned int' to 'long unsigned int' changes value from '17179869184' to '0' [-Woverflow]
     20 | #define __AC(X,Y)       (X##Y)
        |                         ^~~~~~
  include/uapi/linux/const.h:21:25: note: in expansion of macro '__AC'
     21 | #define _AC(X,Y)        __AC(X,Y)
        |                         ^~~~
  include/linux/sizes.h:56:41: note: in expansion of macro '_AC'
     56 | #define SZ_16G                          _AC(0x400000000, ULL)
        |                                         ^~~
  include/linux/mm.h:2214:43: note: in expansion of macro 'SZ_16G'
   2214 | #define MAX_FOLIO_ORDER         get_order(SZ_16G)
        |                                           ^~~~~~
  include/linux/mm.h:2223:41: note: in expansion of macro 'MAX_FOLIO_ORDER'
   2223 | #define MAX_FOLIO_NR_PAGES      (1UL << MAX_FOLIO_ORDER)
        |                                         ^~~~~~~~~~~~~~~
  mm/util.c:1266:23: note: in expansion of macro 'MAX_FOLIO_NR_PAGES'
   1266 |         if (ps->idx < MAX_FOLIO_NR_PAGES) {
        |                       ^~~~~~~~~~~~~~~~~~

Cheers,
Nathan