linux-kernel - Re: [PATCH 2/3] hugetlb: Use vmf_anon_prepare() instead of anon_vma

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Date: Wed, 21 Feb 2024 03:46:04 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, muchun.song@...ux.dev
Subject: Re: [PATCH 2/3] hugetlb: Use vmf_anon_prepare() instead of
 anon_vma_prepare()

On Tue, Feb 20, 2024 at 03:14:23PM -0800, Vishal Moola (Oracle) wrote:
> +++ b/mm/hugetlb.c
> @@ -5834,9 +5834,15 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>  	struct folio *old_folio;
>  	struct folio *new_folio;
>  	int outside_reserve = 0;
> -	vm_fault_t ret = 0;
> +	vm_fault_t ret = 0, anon_ret = 0;

Do we need a second variable here?  Seems to me like we could
unconditionally assign to ret:

> -	if (unlikely(anon_vma_prepare(vma))) {
> -		ret = VM_FAULT_OOM;
> +	anon_ret = vmf_anon_prepare(&vmf);
> +	if (unlikely(anon_ret)) {
> +		ret = anon_ret;



>  	unsigned long haddr = address & huge_page_mask(h);
>  	struct mmu_notifier_range range;
> +	struct vm_fault vmf = {
> +				.vma = vma,
> +				.address = haddr,
> +				.real_address = address,
> +				.flags = flags,
> +	};

We don't usually indent quite so far.  One extra tab would be enough.

Also, I thought we talked about creating the vmf in hugetlb_fault(),
then passing it to hugetlb_wp() hugetlb_no_page() and handle_userfault()?
Was there a reason to abandon that idea?