Re: [PATCH v7 mm-new 01/10] mm: thp: remove disabled task from khugepaged_mm_slot

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Sep 11, 2025 at 10:28 AM Zi Yan <ziy@nvidia.com> wrote:
>
> On 10 Sep 2025, at 22:12, Lance Yang wrote:
>
> > Hi Yafang,
> >
> > On 2025/9/11 01:27, kernel test robot wrote:
> >> Hi Yafang,
> >>
> >> kernel test robot noticed the following build errors:
> >>
> >> [auto build test ERROR on akpm-mm/mm-everything]
> >>
> >> url:    https://github.com/intel-lab-lkp/linux/commits/Yafang-Shao/mm-thp-remove-disabled-task-from-khugepaged_mm_slot/20250910-144850
> >> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> >> patch link:    https://lore.kernel.org/r/20250910024447.64788-2-laoar.shao%40gmail.com
> >> patch subject: [PATCH v7 mm-new 01/10] mm: thp: remove disabled task from khugepaged_mm_slot
> >> config: x86_64-allnoconfig (https://download.01.org/0day-ci/archive/20250911/202509110109.PSgSHb31-lkp@intel.com/config)
> >> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> >> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250911/202509110109.PSgSHb31-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/202509110109.PSgSHb31-lkp@intel.com/
> >>
> >> All errors (new ones prefixed by >>):
> >>
> >>>> kernel/sys.c:2500:6: error: call to undeclared function 'hugepage_pmd_enabled'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> >>      2500 |             hugepage_pmd_enabled())
> >>           |             ^
> >>>> kernel/sys.c:2501:3: error: call to undeclared function '__khugepaged_enter'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> >>      2501 |                 __khugepaged_enter(mm);
> >>           |                 ^
> >>     2 errors generated.
> >
> > Oops, seems like hugepage_pmd_enabled() and __khugepaged_enter() are only
> > available when CONFIG_TRANSPARENT_HUGEPAGE is enabled ;)
> >
> >>
> >>
> >> vim +/hugepage_pmd_enabled +2500 kernel/sys.c
> >>
> >>    2471
> >>    2472      static int prctl_set_thp_disable(bool thp_disable, unsigned long flags,
> >>    2473                                       unsigned long arg4, unsigned long arg5)
> >>    2474      {
> >>    2475              struct mm_struct *mm = current->mm;
> >>    2476
> >>    2477              if (arg4 || arg5)
> >>    2478                      return -EINVAL;
> >>    2479
> >>    2480              /* Flags are only allowed when disabling. */
> >>    2481              if ((!thp_disable && flags) || (flags & ~PR_THP_DISABLE_EXCEPT_ADVISED))
> >>    2482                      return -EINVAL;
> >>    2483              if (mmap_write_lock_killable(current->mm))
> >>    2484                      return -EINTR;
> >>    2485              if (thp_disable) {
> >>    2486                      if (flags & PR_THP_DISABLE_EXCEPT_ADVISED) {
> >>    2487                              mm_flags_clear(MMF_DISABLE_THP_COMPLETELY, mm);
> >>    2488                              mm_flags_set(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
> >>    2489                      } else {
> >>    2490                              mm_flags_set(MMF_DISABLE_THP_COMPLETELY, mm);
> >>    2491                              mm_flags_clear(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
> >>    2492                      }
> >>    2493              } else {
> >>    2494                      mm_flags_clear(MMF_DISABLE_THP_COMPLETELY, mm);
> >>    2495                      mm_flags_clear(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
> >>    2496              }
> >>    2497
> >>    2498              if (!mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm) &&
> >>    2499                  !mm_flags_test(MMF_VM_HUGEPAGE, mm) &&
> >>> 2500                    hugepage_pmd_enabled())
> >>> 2501                        __khugepaged_enter(mm);
> >>    2502              mmap_write_unlock(current->mm);
> >>    2503              return 0;
> >>    2504      }
> >>    2505
> >
> > So, let's wrap the new logic in an #ifdef CONFIG_TRANSPARENT_HUGEPAGE block.
> >
> > diff --git a/kernel/sys.c b/kernel/sys.c
> > index a1c1e8007f2d..c8600e017933 100644
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -2495,10 +2495,13 @@ static int prctl_set_thp_disable(bool thp_disable, unsigned long flags,
> >                 mm_flags_clear(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
> >         }
> >
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >         if (!mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm) &&
> >             !mm_flags_test(MMF_VM_HUGEPAGE, mm) &&
> >             hugepage_pmd_enabled())
> >                 __khugepaged_enter(mm);
> > +#endif
> > +
> >         mmap_write_unlock(current->mm);
> >         return 0;
> >  }
>
> Or in the header file,
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> ...
> #else
> bool hugepage_pmd_enabled()
> {
>         return false;
> }
>
> int __khugepaged_enter(struct mm_struct *mm)
> {
>         return 0;
> }
> #endif

Thank you, both. I will address this in the next version.

-- 
Regards
Yafang