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

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Date: Sun, 7 Apr 2024 16:59:13 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Vishal Moola <vishal.moola@...il.com>
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 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.

Muchun,
Thanks.