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

[Zi Yan <ziy@nvidia.com>]

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

Best Regards,
Yan, Zi