Re: [PATCH v7 04/17] mm: modify vma_iter_store{_gfp} to indicate if it's storing a new vma

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Jan 7, 2025 at 8:50 AM Liam R. Howlett <Liam.Howlett@oracle.com> wrote:
>
> * Suren Baghdasaryan <surenb@google.com> [241226 12:07]:
> > vma_iter_store() functions can be used both when adding a new vma and
> > when updating an existing one. However for existing ones we do not need
> > to mark them attached as they are already marked that way. Add a parameter
> > to distinguish the usage and skip vma_mark_attached() when not needed.
>
> I really don't like boolean flags - especially to such a small function.
>
> The passing of flags complicates things and is not self documenting. Can
> we make a new vma_iter_store_detach() that just calls vma_iter_store()
> then does the detach?

Sure, I'll do that. Thanks for the feedback!

>
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  include/linux/mm.h | 12 ++++++++++++
> >  mm/nommu.c         |  4 ++--
> >  mm/vma.c           | 16 ++++++++--------
> >  mm/vma.h           | 13 +++++++++----
> >  4 files changed, 31 insertions(+), 14 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 081178b0eec4..c50edfedd99d 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -821,6 +821,16 @@ static inline void vma_assert_locked(struct vm_area_struct *vma)
> >               vma_assert_write_locked(vma);
> >  }
> >
> > +static inline void vma_assert_attached(struct vm_area_struct *vma)
> > +{
> > +     VM_BUG_ON_VMA(vma->detached, vma);
> > +}
> > +
> > +static inline void vma_assert_detached(struct vm_area_struct *vma)
> > +{
> > +     VM_BUG_ON_VMA(!vma->detached, vma);
> > +}
> > +
> >  static inline void vma_mark_attached(struct vm_area_struct *vma)
> >  {
> >       vma->detached = false;
> > @@ -866,6 +876,8 @@ 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)
> >               { mmap_assert_write_locked(vma->vm_mm); }
> > +static inline void vma_assert_attached(struct vm_area_struct *vma) {}
> > +static inline void vma_assert_detached(struct vm_area_struct *vma) {}
> >  static inline void vma_mark_attached(struct vm_area_struct *vma) {}
> >  static inline void vma_mark_detached(struct vm_area_struct *vma) {}
> >
> > diff --git a/mm/nommu.c b/mm/nommu.c
> > index 9cb6e99215e2..72c8c505836c 100644
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -1191,7 +1191,7 @@ unsigned long do_mmap(struct file *file,
> >       setup_vma_to_mm(vma, current->mm);
> >       current->mm->map_count++;
> >       /* add the VMA to the tree */
> > -     vma_iter_store(&vmi, vma);
> > +     vma_iter_store(&vmi, vma, true);
> >
> >       /* we flush the region from the icache only when the first executable
> >        * mapping of it is made  */
> > @@ -1356,7 +1356,7 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >
> >       setup_vma_to_mm(vma, mm);
> >       setup_vma_to_mm(new, mm);
> > -     vma_iter_store(vmi, new);
> > +     vma_iter_store(vmi, new, true);
> >       mm->map_count++;
> >       return 0;
> >
> > diff --git a/mm/vma.c b/mm/vma.c
> > index 476146c25283..ce113dd8c471 100644
> > --- a/mm/vma.c
> > +++ b/mm/vma.c
> > @@ -306,7 +306,7 @@ static void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi,
> >                * us to insert it before dropping the locks
> >                * (it may either follow vma or precede it).
> >                */
> > -             vma_iter_store(vmi, vp->insert);
> > +             vma_iter_store(vmi, vp->insert, true);
> >               mm->map_count++;
> >       }
> >
> > @@ -660,14 +660,14 @@ static int commit_merge(struct vma_merge_struct *vmg,
> >       vma_set_range(vmg->vma, vmg->start, vmg->end, vmg->pgoff);
> >
> >       if (expanded)
> > -             vma_iter_store(vmg->vmi, vmg->vma);
> > +             vma_iter_store(vmg->vmi, vmg->vma, false);
> >
> >       if (adj_start) {
> >               adjust->vm_start += adj_start;
> >               adjust->vm_pgoff += PHYS_PFN(adj_start);
> >               if (adj_start < 0) {
> >                       WARN_ON(expanded);
> > -                     vma_iter_store(vmg->vmi, adjust);
> > +                     vma_iter_store(vmg->vmi, adjust, false);
> >               }
> >       }
> >
> > @@ -1689,7 +1689,7 @@ int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
> >               return -ENOMEM;
> >
> >       vma_start_write(vma);
> > -     vma_iter_store(&vmi, vma);
> > +     vma_iter_store(&vmi, vma, true);
> >       vma_link_file(vma);
> >       mm->map_count++;
> >       validate_mm(mm);
> > @@ -2368,7 +2368,7 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap)
> >
> >       /* Lock the VMA since it is modified after insertion into VMA tree */
> >       vma_start_write(vma);
> > -     vma_iter_store(vmi, vma);
> > +     vma_iter_store(vmi, vma, true);
> >       map->mm->map_count++;
> >       vma_link_file(vma);
> >
> > @@ -2542,7 +2542,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >       vm_flags_init(vma, flags);
> >       vma->vm_page_prot = vm_get_page_prot(flags);
> >       vma_start_write(vma);
> > -     if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
> > +     if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL, true))
> >               goto mas_store_fail;
> >
> >       mm->map_count++;
> > @@ -2785,7 +2785,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
> >                               anon_vma_interval_tree_pre_update_vma(vma);
> >                               vma->vm_end = address;
> >                               /* Overwrite old entry in mtree. */
> > -                             vma_iter_store(&vmi, vma);
> > +                             vma_iter_store(&vmi, vma, false);
> >                               anon_vma_interval_tree_post_update_vma(vma);
> >
> >                               perf_event_mmap(vma);
> > @@ -2865,7 +2865,7 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address)
> >                               vma->vm_start = address;
> >                               vma->vm_pgoff -= grow;
> >                               /* Overwrite old entry in mtree. */
> > -                             vma_iter_store(&vmi, vma);
> > +                             vma_iter_store(&vmi, vma, false);
> >                               anon_vma_interval_tree_post_update_vma(vma);
> >
> >                               perf_event_mmap(vma);
> > diff --git a/mm/vma.h b/mm/vma.h
> > index 24636a2b0acf..18c9e49b1eae 100644
> > --- a/mm/vma.h
> > +++ b/mm/vma.h
> > @@ -145,7 +145,7 @@ __must_check int vma_shrink(struct vma_iterator *vmi,
> >               unsigned long start, unsigned long end, pgoff_t pgoff);
> >
> >  static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
> > -                     struct vm_area_struct *vma, gfp_t gfp)
> > +                     struct vm_area_struct *vma, gfp_t gfp, bool new_vma)
> >
> >  {
> >       if (vmi->mas.status != ma_start &&
> > @@ -157,7 +157,10 @@ static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
> >       if (unlikely(mas_is_err(&vmi->mas)))
> >               return -ENOMEM;
> >
> > -     vma_mark_attached(vma);
> > +     if (new_vma)
> > +             vma_mark_attached(vma);
> > +     vma_assert_attached(vma);
> > +
> >       return 0;
> >  }
> >
> > @@ -366,7 +369,7 @@ static inline struct vm_area_struct *vma_iter_load(struct vma_iterator *vmi)
> >
> >  /* Store a VMA with preallocated memory */
> >  static inline void vma_iter_store(struct vma_iterator *vmi,
> > -                               struct vm_area_struct *vma)
> > +                               struct vm_area_struct *vma, bool new_vma)
> >  {
> >
> >  #if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
> > @@ -390,7 +393,9 @@ static inline void vma_iter_store(struct vma_iterator *vmi,
> >
> >       __mas_set_range(&vmi->mas, vma->vm_start, vma->vm_end - 1);
> >       mas_store_prealloc(&vmi->mas, vma);
> > -     vma_mark_attached(vma);
> > +     if (new_vma)
> > +             vma_mark_attached(vma);
> > +     vma_assert_attached(vma);
> >  }
> >
> >  static inline unsigned long vma_iter_addr(struct vma_iterator *vmi)
> > --
> > 2.47.1.613.gc27f4b7a9f-goog
> >