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

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

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;
  }

Cheers,
Lance