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

[Yafang Shao <laoar.shao@gmail.com>]

On Wed, Sep 10, 2025 at 1:11 PM Lance Yang <lance.yang@linux.dev> wrote:
>
> Hey Yafang,
>
> On 2025/9/10 10:44, Yafang Shao wrote:
> > Since a task with MMF_DISABLE_THP_COMPLETELY cannot use THP, remove it from
> > the khugepaged_mm_slot to stop khugepaged from processing it.
> >
> > After this change, the following semantic relationship always holds:
> >
> >    MMF_VM_HUGEPAGE is set     == task is in khugepaged mm_slot
> >    MMF_VM_HUGEPAGE is not set == task is not in khugepaged mm_slot
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > Cc: Lance Yang <ioworker0@gmail.com>
> > ---
> >   include/linux/khugepaged.h |  1 +
> >   kernel/sys.c               |  6 ++++++
> >   mm/khugepaged.c            | 19 +++++++++----------
> >   3 files changed, 16 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
> > index eb1946a70cff..6cb9107f1006 100644
> > --- a/include/linux/khugepaged.h
> > +++ b/include/linux/khugepaged.h
> > @@ -19,6 +19,7 @@ extern void khugepaged_min_free_kbytes_update(void);
> >   extern bool current_is_khugepaged(void);
> >   extern int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> >                                  bool install_pmd);
> > +bool hugepage_pmd_enabled(void);
> >
> >   static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
> >   {
> > diff --git a/kernel/sys.c b/kernel/sys.c
> > index a46d9b75880b..a1c1e8007f2d 100644
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -8,6 +8,7 @@
> >   #include <linux/export.h>
> >   #include <linux/mm.h>
> >   #include <linux/mm_inline.h>
> > +#include <linux/khugepaged.h>
> >   #include <linux/utsname.h>
> >   #include <linux/mman.h>
> >   #include <linux/reboot.h>
> > @@ -2493,6 +2494,11 @@ static int prctl_set_thp_disable(bool thp_disable, unsigned long flags,
> >               mm_flags_clear(MMF_DISABLE_THP_COMPLETELY, mm);
> >               mm_flags_clear(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
> >       }
> > +
> > +     if (!mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm) &&
> > +         !mm_flags_test(MMF_VM_HUGEPAGE, mm) &&
> > +         hugepage_pmd_enabled())
> > +             __khugepaged_enter(mm);
> >       mmap_write_unlock(current->mm);
>
> One minor style suggestion for prctl_set_thp_disable():
>
> static int prctl_set_thp_disable(bool thp_disable, unsigned long flags,
>                                  unsigned long arg4, unsigned long arg5)
> {
>         struct mm_struct *mm = current->mm;
>
>         [...]
>         if (mmap_write_lock_killable(current->mm))
>                 return -EINTR;
>         [...]
>         mmap_write_unlock(current->mm);
>         return 0;
> }
>
> It initializes struct mm_struct *mm = current->mm; at the beginning, but
> then uses both mm and current->mm. Could you change the calls using
> current->mm to use the local mm variable for consistency? Just a nit ;)

Nice catch

Hello Andrew, David,

The original commit "prctl: extend PR_SET_THP_DISABLE to optionally
exclude VM_HUGEPAGE" is still in mm-new branch. The change below is a
minor cleanup for it.

Could we please fold this change directly into the original commit to
keep the history clean?

diff --git a/kernel/sys.c b/kernel/sys.c
index a46d9b7..2250a32 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2479,7 +2479,7 @@ static int prctl_set_thp_disable(bool
thp_disable, unsigned long flags,
        /* Flags are only allowed when disabling. */
        if ((!thp_disable && flags) || (flags & ~PR_THP_DISABLE_EXCEPT_ADVISED))
                return -EINVAL;
-       if (mmap_write_lock_killable(current->mm))
+       if (mmap_write_lock_killable(mm))
                return -EINTR;
        if (thp_disable) {
                if (flags & PR_THP_DISABLE_EXCEPT_ADVISED) {
@@ -2493,7 +2493,7 @@ static int prctl_set_thp_disable(bool
thp_disable, unsigned long flags,
                mm_flags_clear(MMF_DISABLE_THP_COMPLETELY, mm);
                mm_flags_clear(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
        }
-       mmap_write_unlock(current->mm);
+       mmap_write_unlock(mm);
        return 0;
 }


-- 
Regards
Yafang