[PATCH v2 6/7] mm/vmalloc: align vm_area so vmap() can batch mappings

[Barry Song]

On Wed, May 20, 2026 at 3:37 PM Uladzislau Rezki <urezki at gmail.com> wrote:
>
> On Thu, May 14, 2026 at 05:41:07PM +0800, Wen Jiang wrote:
> > From: "Barry Song (Xiaomi)" <baohua at kernel.org>
> >
> > 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 at kernel.org>
> > Signed-off-by: Wen Jiang <jiangwen6 at xiaomi.com>
> > Tested-by: Xueyuan Chen <xueyuan.chen21 at gmail.com>
> > ---
> >  mm/vmalloc.c | 31 ++++++++++++++++++++++++++++++-
> >  1 file changed, 30 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index c30a7673e..b3389c8f1 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3591,6 +3591,35 @@ static int __vmap_huge(unsigned long addr, unsigned long end,
> >       return err;
> >  }
> >
> > +static struct vm_struct *get_aligned_vm_area(unsigned long size, unsigned long flags)
> > +{
> > +     unsigned int shift = (size >= PMD_SIZE) ? PMD_SHIFT :
> > +                             arch_vmap_pte_supported_shift(size);
> > +     struct vm_struct *vm_area = NULL;
> > +
> > +     /*
> > +      * Try to allocate an aligned vm_area so contiguous pages can be
> > +      * mapped in batches.
> > +      */
> > +     while (1) {
> > +             unsigned long align = 1UL << shift;
> > +
> > +             vm_area = __get_vm_area_node(size, align, PAGE_SHIFT, flags,
> > +                             VMALLOC_START, VMALLOC_END,
> > +                             NUMA_NO_NODE, GFP_KERNEL,
> > +                             __builtin_return_address(0));
> > +             if (vm_area || shift <= PAGE_SHIFT)
> > +                     goto out;
> > +             if (shift == PMD_SHIFT)
> > +                     shift = arch_vmap_pte_supported_shift(size);
> > +             else if (shift > PAGE_SHIFT)
> > +                     shift = PAGE_SHIFT;
> > +     }
> > +
> > +out:
> > +     return vm_area;
> > +}
> > +
> IMO, we should get rid of this while(1) loop. It looks like you need to
> handle just few cases. 3?

Hi Uladzislau,

I don’t quite understand what you mean — are you suggesting
calling __get_vm_area_node() three times? We try 2MB first,
then 64KB, and finally 4KB. If 2MB succeeds, there is no
reason to try 64KB. Likewise, if 64KB succeeds, there is no
need to fall back to 4KB.

>
>
> shift min value is PAGE_SHIFT, could you please clarify when it can be less?

I guess this should be changed to "==" ?

Thanks
Barry