Re: [PATCH v3 6/6] mm/vmalloc: align vm_area so vmap() can batch mappings

[Wen Jiang]

On Wed, 27 May 2026 at 14:25, Dev Jain <dev.jain@xxxxxxx> wrote:
>
>
>
> On 22/05/26 11:01 am, Wen Jiang wrote:
> > From: "Barry Song (Xiaomi)" <baohua@xxxxxxxxxx>
> >
> > Try to align the vmap virtual address to PMD_SHIFT or a
> > larger PTE mapping size hinted by the architecture, so
> > contiguous pages can be batch-mapped when setting PMD or
> > PTE entries.
> >
> > Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> > Signed-off-by: Wen Jiang <jiangwen6@xxxxxxxxxx>
> > Tested-by: Xueyuan Chen <xueyuan.chen21@xxxxxxxxx>
>
>
> Hmm okay I would have preferred to squash this in the previous, but
> the correctness of previous patch does not rely on this, so it's fine.
>
> > ---
> >  mm/vmalloc.c | 33 ++++++++++++++++++++++++++++++++-
> >  1 file changed, 32 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 50642246f4d40..040d400928aab 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3620,6 +3620,37 @@ static int vmap_batched(unsigned long addr, unsigned long end,
> >       return err;
> >  }
> >
>
> This is screaming for a helper :)
>
> > +static struct vm_struct *get_aligned_vm_area(unsigned long size,
> > +             unsigned long flags, const void *caller)
>
>
> Call this vmap_get_aligned_vm_area, then ...
>
>

Will rename  get_aligned_vm_area to vmap_get_aligned_vm_area.

> > +{
> > +     struct vm_struct *vm_area;
> > +     unsigned int shift;
> > +
> > +     /* Try PMD alignment for large sizes */
> > +     if (size >= PMD_SIZE) {
> > +             vm_area = __get_vm_area_node(size, PMD_SIZE, PAGE_SHIFT, flags,
> > +                             VMALLOC_START, VMALLOC_END,
> > +                             NUMA_NO_NODE, GFP_KERNEL, caller);
>
> Add a wrapper over this called __get_vm_area_node_aligned_caller, which can
> call __get_vm_area_node() with all other arguments fixed, except "align".
>

Will add a __get_vm_area_node_aligned_caller. Will send in v4.

Thanks,
Wen
> > +             if (vm_area)
> > +                     return vm_area;
> > +     }
> > +
> > +     /* Try CONT_PTE alignment */
> > +     shift = arch_vmap_pte_supported_shift(size);
> > +     if (shift > PAGE_SHIFT) {
> > +             vm_area = __get_vm_area_node(size, 1UL << shift, PAGE_SHIFT, flags,
> > +                             VMALLOC_START, VMALLOC_END,
> > +                             NUMA_NO_NODE, GFP_KERNEL, caller);
> > +             if (vm_area)
> > +                     return vm_area;
> > +     }
> > +
> > +     /* Fall back to page alignment */
> > +     return __get_vm_area_node(size, PAGE_SIZE, PAGE_SHIFT, flags,
> > +                     VMALLOC_START, VMALLOC_END,
> > +                     NUMA_NO_NODE, GFP_KERNEL, caller);
> > +}
> > +
> >  /**
> >   * vmap - map an array of pages into virtually contiguous space
> >   * @pages: array of page pointers
> > @@ -3658,7 +3689,7 @@ void *vmap(struct page **pages, unsigned int count,
> >               return NULL;
> >
> >       size = (unsigned long)count << PAGE_SHIFT;
> > -     area = get_vm_area_caller(size, flags, __builtin_return_address(0));
> > +     area = get_aligned_vm_area(size, flags, __builtin_return_address(0));
> >       if (!area)
> >               return NULL;
> >
>