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 9:47 PM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
>
> On Wed, Sep 10, 2025 at 10:28:30PM -0400, Zi Yan 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;
> > }
>
> It seems we have a convention of just not implementing things here if they're
> necessarily used in core code paths (and _with my suggested change_) it's _just_
> khugepaged that's invoking them).
>
> Anyway with my suggestion we can fix this entirely with:
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>
> void khugepaged_enter_mm(struct mm_struct *mm);
>
> #else
>
> void khugepaged_enter_mm(struct mm_struct *mm)
> {
> }
>
> #endif

ack

Thanks for all the suggestions.

-- 
Regards
Yafang