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

Jason Gunthorpe
2025-09-08T13:11:28Z

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?

Then no need to introduce complete. I think it is probably better to
try to avoid using complete except for filling PTEs..

Jason