On Thu, Sep 11, 2025 at 9:47 PM Lorenzo Stoakes
[off-list ref] wrote:

On Wed, Sep 10, 2025 at 10:28:30PM -0400, Zi Yan wrote:

quoted

On 10 Sep 2025, at 22:12, Lance Yang wrote:

quoted

Hi Yafang,

On 2025/9/11 01:27, kernel test robot wrote:

quoted

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 [off-list ref]
| Closes: https://lore.kernel.org/oe-kbuild-all/202509110109.PSgSHb31-lkp@intel.com/ (local)

All errors (new ones prefixed by >>):

quoted

quoted

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())
          |             ^

quoted

quoted

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 ;)

quoted

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) &&

quoted

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