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

[Lance Yang <lance.yang@linux.dev>]

On 2025/9/11 10:28, 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;
> }
> #endif

Nice. That's a much better approach.