linux-kernel - Re: [PATCH v2 2/3] hugetlb: Convert hugetlb_no_page() to use struct vm

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Date: Mon, 8 Apr 2024 10:45:27 -0700
From: Vishal Moola <vishal.moola@...il.com>
To: Muchun Song <muchun.song@...ux.dev>
Cc: Oscar Salvador <osalvador@...e.de>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: Re: [PATCH v2 2/3] hugetlb: Convert hugetlb_no_page() to use struct
 vm_fault

On Sun, Apr 07, 2024 at 04:59:13PM +0800, Muchun Song wrote:
> 
> 
> > On Apr 5, 2024, at 03:58, Vishal Moola <vishal.moola@...il.com> wrote:
> > 
> > On Thu, Apr 4, 2024 at 5:49 AM Oscar Salvador <osalvador@...e.de> wrote:
> >> 
> >> On Mon, Apr 01, 2024 at 01:26:50PM -0700, Vishal Moola (Oracle) wrote:
> >>> hugetlb_no_page() can use the struct vm_fault passed in from
> >>> hugetlb_fault(). This alleviates the stack by consolidating 7
> >>> variables into a single struct.
> >>> 
> >>> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> >>> ---
> >>> mm/hugetlb.c | 59 ++++++++++++++++++++++++++--------------------------
> >>> 1 file changed, 29 insertions(+), 30 deletions(-)
> >>> 
> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> >>> index 360b82374a89..aca2f11b4138 100644
> >>> --- a/mm/hugetlb.c
> >>> +++ b/mm/hugetlb.c
> >>> @@ -6189,9 +6189,7 @@ static bool hugetlb_pte_stable(struct hstate *h, struct mm_struct *mm,
> >>> 
> >>> static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> >>>                      struct vm_area_struct *vma,
> >>> -                     struct address_space *mapping, pgoff_t idx,
> >>> -                     unsigned long address, pte_t *ptep,
> >>> -                     pte_t old_pte, unsigned int flags,
> >>> +                     struct address_space *mapping,
> >> 
> >> AFAICS all this can be self-contained in vm_fault struct.
> >> vmf->vma->mm and vmf->vma.
> >> I mean, if we want to convert this interface, why not going all the way?
> >> 
> >> Looks a bit odd some fields yes while some others remain.
> >> 
> >> Or am I missing something?
> > 
> > Mainly just minimizing code churn, we would either unnecessarily
> > change multiple lines using vma or have to declare the variables
> > again anyways (or have extra churn I didn't like).
> 
> I don't think adding some variables is a problem. I suppose the compiler
> could do some optimization for us. So I think it is better to pass
> only one argument vmf to hugetlb_no_page(). Otherwise, LGTM.

Alright we can get rid of the vm_area_struct and mm_struct arguments as
well.

Andrew, could you please fold the attached patch into this one? 

View attachment "0001-hugetlb-Simplify-hugetlb_no_page-arguments.patch" of type "text/plain" (1515 bytes)