On Wed, Sep 10, 2025 at 1:11 PM Lance Yang <lance.yang@xxxxxxxxx> 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@xxxxxxxxx>
> > Cc: Lance Yang <ioworker0@xxxxxxxxx>
> > ---
> > 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
