Re: [PATCH v2 2/8] mm/rmap: skip unfaulted VMAs on anon_vma clone, unlink

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Jan 6, 2026 at 10:34 AM Liam R. Howlett <Liam.Howlett@oracle.com> wrote:
>
> * Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [260106 10:04]:
> > For both anon_vma_clone() and unlink_anon_vmas(), if the source VMA or the
> > VMA to be linked are unfaulted (e.g. !vma->anon_vma), then the functions do
> > nothing. Simply exit early in these cases.
> >
> > In the unlink_anon_vmas() case we can also remove a conditional that checks
> > whether vma->anon_vma is set.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>
> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

>
> > ---
> >  mm/rmap.c | 22 +++++++++++++---------
> >  1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 54ccf884d90a..de2cbe860566 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -314,6 +314,9 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
> >
> >       check_anon_vma_clone(dst, src);
> >
> > +     if (!src->anon_vma)
> > +             return 0;
> > +
> >       list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
> >               struct anon_vma *anon_vma;
> >
> > @@ -474,7 +477,10 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
> >       mmap_assert_locked(vma->vm_mm);
> >
> >       /* Unfaulted is a no-op. */
> > -     VM_WARN_ON_ONCE(!vma->anon_vma && !list_empty(&vma->anon_vma_chain));
> > +     if (!vma->anon_vma) {
> > +             VM_WARN_ON_ONCE(!list_empty(&vma->anon_vma_chain));
> > +             return;
> > +     }
> >
> >       /*
> >        * Unlink each anon_vma chained to the VMA.  This list is ordered
> > @@ -498,15 +504,13 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
> >               list_del(&avc->same_vma);
> >               anon_vma_chain_free(avc);
> >       }
> > -     if (vma->anon_vma) {
> > -             vma->anon_vma->num_active_vmas--;
> >
> > -             /*
> > -              * vma would still be needed after unlink, and anon_vma will be prepared
> > -              * when handle fault.
> > -              */
> > -             vma->anon_vma = NULL;
> > -     }
> > +     vma->anon_vma->num_active_vmas--;
> > +     /*
> > +      * vma would still be needed after unlink, and anon_vma will be prepared
> > +      * when handle fault.
> > +      */
> > +     vma->anon_vma = NULL;
> >       unlock_anon_vma_root(root);
> >
> >       /*
> > --
> > 2.52.0
> >