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References: <20200626223130.199227-1-peterx@redhat.com> <20200626223130.199227-13-peterx@redhat.com>
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From:   Greentime Hu <green.hu@gmail.com>
Date:   Sat, 27 Jun 2020 10:59:03 +0800
Message-ID: <CAEbi=3eMG5R9dC+xZvFrzMSjvwber1YOa6-Aa3Ww0ksbeeCUfQ@mail.gmail.com>
Subject: Re: [PATCH 12/26] mm/nds32: Use general page fault accounting
To:     Peter Xu <peterx@redhat.com>
Cc:     Linux Memory Management List <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Gerald Schaefer <gerald.schaefer@de.ibm.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nick Hu <nickhu@andestech.com>,
        Vincent Chen <deanbo422@gmail.com>
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Peter Xu <peterx@redhat.com> =E6=96=BC 2020=E5=B9=B46=E6=9C=8827=E6=97=A5 =
=E9=80=B1=E5=85=AD =E4=B8=8A=E5=8D=886:31=E5=AF=AB=E9=81=93=EF=BC=9A
>
> Use the general page fault accounting by passing regs into handle_mm_faul=
t().
> It naturally solve the issue of multiple page fault accounting when page =
fault
> retry happened.
>
> Fix PERF_COUNT_SW_PAGE_FAULTS perf event manually for page fault retries,=
 by
> moving it before taking mmap_sem.
>
> CC: Nick Hu <nickhu@andestech.com>
> CC: Greentime Hu <green.hu@gmail.com>
> CC: Vincent Chen <deanbo422@gmail.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  arch/nds32/mm/fault.c | 19 +++----------------
>  1 file changed, 3 insertions(+), 16 deletions(-)
>
> diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c
> index 22527129025c..e7344440623c 100644
> --- a/arch/nds32/mm/fault.c
> +++ b/arch/nds32/mm/fault.c
> @@ -122,6 +122,8 @@ void do_page_fault(unsigned long entry, unsigned long=
 addr,
>         if (unlikely(faulthandler_disabled() || !mm))
>                 goto no_context;
>
> +       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
> +
>         /*
>          * As per x86, we may deadlock here. However, since the kernel on=
ly
>          * validly references user space from well defined areas of the c=
ode,
> @@ -207,7 +209,7 @@ void do_page_fault(unsigned long entry, unsigned long=
 addr,
>          * the fault.
>          */
>
> -       fault =3D handle_mm_fault(vma, addr, flags, NULL);
> +       fault =3D handle_mm_fault(vma, addr, flags, regs);
>
>         /*
>          * If we need to retry but a fatal signal is pending, handle the
> @@ -229,22 +231,7 @@ void do_page_fault(unsigned long entry, unsigned lon=
g addr,
>                         goto bad_area;
>         }
>
> -       /*
> -        * Major/minor page fault accounting is only done on the initial
> -        * attempt. If we go through a retry, it is extremely likely that=
 the
> -        * page will be found in page cache at that point.
> -        */
> -       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
>         if (flags & FAULT_FLAG_ALLOW_RETRY) {
> -               if (fault & VM_FAULT_MAJOR) {
> -                       tsk->maj_flt++;
> -                       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ,
> -                                     1, regs, addr);
> -               } else {
> -                       tsk->min_flt++;
> -                       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN,
> -                                     1, regs, addr);
> -               }
>                 if (fault & VM_FAULT_RETRY) {
>                         flags |=3D FAULT_FLAG_TRIED;
>

Hi Peter,

Thank you.
Acked-by: Greentime Hu <green.hu@gmail.com>