[PATCH v3 24/35] mm: introduce vma detached flag

[Suren Baghdasaryan]

On Thu, Feb 23, 2023 at 12:08 PM Liam R. Howlett
<Liam.Howlett at oracle.com> wrote:
>
>
> Can we change this to active/inactive?  I think there is potential for
> reusing this functionality to even larger degrees and that name would
> fit better and would still make sense in this context.
>
> ie: vma_mark_active() and vma_mark_inactive() ?

Those names sound too generic (not obvious what active/inactive
means), while detached/isolated I think is more clear and specific.
Does not really make a huge difference to me but maybe you can come up
with better naming that addresses my concern and meets your usecase?

>
> * Suren Baghdasaryan <surenb at google.com> [230216 00:18]:
> > Per-vma locking mechanism will search for VMA under RCU protection and
> > then after locking it, has to ensure it was not removed from the VMA
> > tree after we found it. To make this check efficient, introduce a
> > vma->detached flag to mark VMAs which were removed from the VMA tree.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb at google.com>
> > ---
> >  include/linux/mm.h       | 11 +++++++++++
> >  include/linux/mm_types.h |  3 +++
> >  mm/mmap.c                |  2 ++
> >  3 files changed, 16 insertions(+)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index f4f702224ec5..3f98344f829c 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -693,6 +693,14 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma)
> >       VM_BUG_ON_VMA(vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq), vma);
> >  }
> >
> > +static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached)
> > +{
> > +     /* When detaching vma should be write-locked */
> > +     if (detached)
> > +             vma_assert_write_locked(vma);
> > +     vma->detached = detached;
> > +}
> > +
> >  #else /* CONFIG_PER_VMA_LOCK */
> >
> >  static inline void vma_init_lock(struct vm_area_struct *vma) {}
> > @@ -701,6 +709,8 @@ static inline bool vma_start_read(struct vm_area_struct *vma)
> >  static inline void vma_end_read(struct vm_area_struct *vma) {}
> >  static inline void vma_start_write(struct vm_area_struct *vma) {}
> >  static inline void vma_assert_write_locked(struct vm_area_struct *vma) {}
> > +static inline void vma_mark_detached(struct vm_area_struct *vma,
> > +                                  bool detached) {}
> >
> >  #endif /* CONFIG_PER_VMA_LOCK */
> >
> > @@ -712,6 +722,7 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
> >       vma->vm_mm = mm;
> >       vma->vm_ops = &dummy_vm_ops;
> >       INIT_LIST_HEAD(&vma->anon_vma_chain);
> > +     vma_mark_detached(vma, false);
> >       vma_init_lock(vma);
> >  }
> >
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index e268723eaf44..939f4f5a1115 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -511,6 +511,9 @@ struct vm_area_struct {
> >  #ifdef CONFIG_PER_VMA_LOCK
> >       int vm_lock_seq;
> >       struct rw_semaphore lock;
> > +
> > +     /* Flag to indicate areas detached from the mm->mm_mt tree */
> > +     bool detached;
> >  #endif
> >
> >       /*
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 801608726be8..adf40177e68f 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -593,6 +593,7 @@ static inline void vma_complete(struct vma_prepare *vp,
> >
> >       if (vp->remove) {
> >  again:
> > +             vma_mark_detached(vp->remove, true);
> >               if (vp->file) {
> >                       uprobe_munmap(vp->remove, vp->remove->vm_start,
> >                                     vp->remove->vm_end);
> > @@ -2267,6 +2268,7 @@ static inline int munmap_sidetree(struct vm_area_struct *vma,
> >       if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> >               return -ENOMEM;
> >
> > +     vma_mark_detached(vma, true);
> >       if (vma->vm_flags & VM_LOCKED)
> >               vma->vm_mm->locked_vm -= vma_pages(vma);
> >
> > --
> > 2.39.1
> >
>
> --
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