Re: [PATCH v4 4/7] proc/task_mmu: remove special-casing of smap_gather_stats() start parameter

[Suren Baghdasaryan]

On Fri, Sep 11, 2026 at 12:45 PM Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx> wrote:
>
> On Fri, Sep 11, 2026 at 12:41:42PM -0700, Suren Baghdasaryan wrote:
> > smap_gather_stats() interprets its start parameter to mean vma->vm_start
> > when it's set to 0. Eliminate this special interpretation and provide two
> > separate functions for a partial and complete VMA walk.
> >
> > Since smap_gather_stats() operates within a single VMA, we can replace
> > walk_page_vma()/walk_page_range() calls with walk_page_range_vma()
> > which is simpler and also can be called while holding per-VMA lock.
> >
> > No functional change intended.
> >
> > Suggested by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
>
> LGTM so:
>
> Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

Thanks!

>
> > ---
> >  fs/proc/task_mmu.c | 52 +++++++++++++++++++++++++++++++---------------
> >  1 file changed, 35 insertions(+), 17 deletions(-)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 0e53eb065a3e..a6026ffd07f1 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -1246,20 +1246,26 @@ get_smaps_shmem_walk_ops(struct proc_maps_private *priv)
> >       return &smaps_shmem_walk_vma_lock_ops;
> >  }
> >
> > -/*
> > - * Gather mem stats from @vma with the indicated beginning
> > - * address @start, and keep them in @mss.
> > +/**
> > + * smap_gather_stats_range() - Gather mem stats from a portion of the @vma.
> > + * @priv: proc maps private state.
> > + * @vma: The VMA to gather stats for.
> > + * @mss: The accumulated stats.
> > + * @start: The address from which to start.
> >   *
> > - * Use vm_start of @vma as the beginning address if @start is 0.
> > + * This gathers stats for the portion of the VMA starting at the @start
> > + * address.
> >   */
> > -static void smap_gather_stats(struct proc_maps_private *priv,
> > -                           struct vm_area_struct *vma,
> > -                           struct mem_size_stats *mss, unsigned long start)
> > +static void smap_gather_stats_range(struct proc_maps_private *priv,
> > +             struct vm_area_struct *vma,
> > +             struct mem_size_stats *mss,
> > +             unsigned long start)
> >  {
> >       const struct mm_walk_ops *ops = get_smaps_walk_ops(priv);
> > +     const bool is_partial = start > vma->vm_start;
> >
> >       /* Invalid start */
> > -     if (start >= vma->vm_end)
> > +     if (start < vma->vm_start || start >= vma->vm_end)
> >               return;
> >
> >       if (vma == get_gate_vma(priv->lock_ctx.mm))
> > @@ -1278,20 +1284,31 @@ static void smap_gather_stats(struct proc_maps_private *priv,
> >               const unsigned long shmem_swapped = shmem_swap_usage(vma);
> >               const bool is_cow = vma_is_cow_mapping(vma);
> >
> > -             if (start || (shmem_swapped && is_cow))
> > +             if (is_partial || (shmem_swapped && is_cow))
> >                       ops = get_smaps_shmem_walk_ops(priv);
> >               else
> >                       mss->swap += shmem_swapped;
> >       }
> >
> > -     if (!start)
> > -             walk_page_vma(vma, ops, mss);
> > -     else
> > -             walk_page_range(vma->vm_mm, start, vma->vm_end, ops, mss);
> > +     walk_page_range_vma(vma, start, vma->vm_end, ops, mss);
> >
> >       reacquire_rcu(priv);
> >  }
> >
> > +/**
> > + * smap_gather_stats() - Gather mem stats from the entire @vma.
> > + * @priv: proc maps private state.
> > + * @vma: The VMA to gather stats for.
> > + * @mss: The accumulated stats.
> > + *
> > + * This gathers stats for the whole of the VMA.
> > + */
> > +static void smap_gather_stats(struct proc_maps_private *priv,
> > +             struct vm_area_struct *vma, struct mem_size_stats *mss)
> > +{
> > +     smap_gather_stats_range(priv, vma, mss, vma->vm_start);
> > +}
> > +
> >  #define SEQ_PUT_DEC(str, val) \
> >               seq_put_decimal_ull_width(m, str, (val) >> 10, 8)
> >
> > @@ -1342,7 +1359,7 @@ static int show_smap(struct seq_file *m, void *v)
> >       struct vm_area_struct *vma = v;
> >       struct mem_size_stats mss = {};
> >
> > -     smap_gather_stats(priv, vma, &mss, 0);
> > +     smap_gather_stats(priv, vma, &mss);
> >
> >       show_map_vma(m, vma);
> >
> > @@ -1395,7 +1412,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
> >
> >       vma_start = vma->vm_start;
> >       do {
> > -             smap_gather_stats(priv, vma, &mss, 0);
> > +             smap_gather_stats(priv, vma, &mss);
> >               last_vma_end = vma->vm_end;
> >
> >               /*
> > @@ -1454,14 +1471,15 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
> >
> >                       /* Case 1 and 2 above */
> >                       if (vma->vm_start >= last_vma_end) {
> > -                             smap_gather_stats(priv, vma, &mss, 0);
> > +                             smap_gather_stats(priv, vma, &mss);
> >                               last_vma_end = vma->vm_end;
> >                               continue;
> >                       }
> >
> >                       /* Case 4 above */
> >                       if (vma->vm_end > last_vma_end) {
> > -                             smap_gather_stats(priv, vma, &mss, last_vma_end);
> > +                             smap_gather_stats_range(priv, vma, &mss,
> > +                                                     last_vma_end);
> >                               last_vma_end = vma->vm_end;
> >                       }
> >               }
> > --
> > 2.55.0.1007.g17ff1f9808-goog
> >
>
> --
> Cheers, Lorenzo