linux-kernel - Re: [PATCH v4 05/26] mm/arm64: Use general page fault accounting

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Message-ID: <20200701073403.GA14692@willie-the-truck>
Date:   Wed, 1 Jul 2020 08:34:04 +0100
From:   Will Deacon <will@...nel.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 05/26] mm/arm64: Use general page fault accounting

On Tue, Jun 30, 2020 at 04:45:14PM -0400, Peter Xu wrote:
> Use the general page fault accounting by passing regs into handle_mm_fault().
> It naturally solve the issue of multiple page fault accounting when page fault
> retry happened.  To do this, we pass pt_regs pointer into __do_page_fault().
> 
> CC: Catalin Marinas <catalin.marinas@....com>
> CC: Will Deacon <will@...nel.org>
> CC: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  arch/arm64/mm/fault.c | 29 ++++++-----------------------
>  1 file changed, 6 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index be29f4076fe3..f07333e86c2f 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -404,7 +404,8 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re
>  #define VM_FAULT_BADACCESS	0x020000
>  
>  static vm_fault_t __do_page_fault(struct mm_struct *mm, unsigned long addr,
> -			   unsigned int mm_flags, unsigned long vm_flags)
> +				  unsigned int mm_flags, unsigned long vm_flags,
> +				  struct pt_regs *regs)
>  {
>  	struct vm_area_struct *vma = find_vma(mm, addr);
>  
> @@ -428,7 +429,7 @@ static vm_fault_t __do_page_fault(struct mm_struct *mm, unsigned long addr,
>  	 */
>  	if (!(vma->vm_flags & vm_flags))
>  		return VM_FAULT_BADACCESS;
> -	return handle_mm_fault(vma, addr & PAGE_MASK, mm_flags, NULL);
> +	return handle_mm_fault(vma, addr & PAGE_MASK, mm_flags, regs);
>  }
>  
>  static bool is_el0_instruction_abort(unsigned int esr)
> @@ -450,7 +451,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  {
>  	const struct fault_info *inf;
>  	struct mm_struct *mm = current->mm;
> -	vm_fault_t fault, major = 0;
> +	vm_fault_t fault;
>  	unsigned long vm_flags = VM_ACCESS_FLAGS;
>  	unsigned int mm_flags = FAULT_FLAG_DEFAULT;
>  
> @@ -516,8 +517,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  #endif
>  	}
>  
> -	fault = __do_page_fault(mm, addr, mm_flags, vm_flags);
> -	major |= fault & VM_FAULT_MAJOR;
> +	fault = __do_page_fault(mm, addr, mm_flags, vm_flags, regs);
>  
>  	/* Quick path to respond to signals */
>  	if (fault_signal_pending(fault, regs)) {
> @@ -538,25 +538,8 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  	 * Handle the "normal" (no error) case first.
>  	 */
>  	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
> -			      VM_FAULT_BADACCESS)))) {
> -		/*
> -		 * Major/minor page fault accounting is only done
> -		 * once. If we go through a retry, it is extremely
> -		 * likely that the page will be found in page cache at
> -		 * that point.
> -		 */
> -		if (major) {
> -			current->maj_flt++;
> -			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs,
> -				      addr);
> -		} else {
> -			current->min_flt++;
> -			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs,
> -				      addr);
> -		}
> -
> +			      VM_FAULT_BADACCESS))))
>  		return 0;
> -	}

Thanks, looks good to me:

Acked-by: Will Deacon <will@...nel.org>

Will