Re: [PATCH 10/16] mm/hugetlb: update hugetlbfs to use mmap_prepare, mmap_complete

Jason Gunthorpe
2025-09-08T13:52:45Z

On Mon, Sep 08, 2025 at 02:37:44PM +0100, Lorenzo Stoakes wrote:
> On Mon, Sep 08, 2025 at 10:11:21AM -0300, Jason Gunthorpe wrote:
> > On Mon, Sep 08, 2025 at 12:10:41PM +0100, Lorenzo Stoakes wrote:
> > > @@ -151,20 +123,55 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
> > > vm_flags |= VM_NORESERVE;
> > >
> > > if (hugetlb_reserve_pages(inode,
> > > - vma->vm_pgoff >> huge_page_order(h),
> > > - len >> huge_page_shift(h), vma,
> > > - vm_flags) < 0)
> > > + vma->vm_pgoff >> huge_page_order(h),
> > > + len >> huge_page_shift(h), vma,
> > > + vm_flags) < 0) {
> >
> > It was split like this because vma is passed here right?
> >
> > But hugetlb_reserve_pages() doesn't do much with the vma:
> >
> > hugetlb_vma_lock_alloc(vma);
> > [..]
> > vma->vm_private_data = vma_lock;
> >
> > Manipulates the private which should already exist in prepare:
> >
> > Check non-share a few times:
> >
> > if (!vma || vma->vm_flags & VM_MAYSHARE) {
> > if (vma && !(vma->vm_flags & VM_MAYSHARE) && h_cg) {
> > if (!vma || vma->vm_flags & VM_MAYSHARE) {
> >
> > And does this resv_map stuff:
> >
> > set_vma_resv_map(vma, resv_map);
> > set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
> > [..]
> > set_vma_private_data(vma, (unsigned long)map);
> >
> > Which is also just manipulating the private data.
> >
> > So it looks to me like it should be refactored so that
> > hugetlb_reserve_pages() returns the priv pointer to set in the VMA
> > instead of accepting vma as an argument. Maybe just pass in the desc
> > instead?
>
> Well hugetlb_vma_lock_alloc() does:
>
> vma_lock->vma = vma;
>
> Which we cannot do in prepare.

Okay, just doing that in commit would be appropriate then

> This is checked in hugetlb_dup_vma_private(), and obviously desc is not a stable
> pointer to be used for comparing anything.
>
> I'm also trying to do the minimal changes I can here, I'd rather not majorly
> refactor things to suit this change if possible.

It doesn't look like a bit refactor, pass vma desc into
hugetlb_reserve_pages(), lift the vma_lock set out

Jason