linux-kernel - Re: [PATCH 10/16] mm/hugetlb: update hugetlbfs to use mmap_prepare, mmap

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Message-ID: <20250908131121.GA616306@nvidia.com>
Date: Mon, 8 Sep 2025 10:11:21 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH 10/16] mm/hugetlb: update hugetlbfs to use mmap_prepare,
 mmap_complete

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