linux-kernel - Re: [PATCH 12/26] mm/nds32: Use general page fault accounting

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Date:   Sat, 27 Jun 2020 10:59:03 +0800
From:   Greentime Hu <green.hu@...il.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nick Hu <nickhu@...estech.com>,
        Vincent Chen <deanbo422@...il.com>
Subject: Re: [PATCH 12/26] mm/nds32: Use general page fault accounting

Peter Xu <peterx@...hat.com> 於 2020年6月27日 週六 上午6:31寫道：
>
> 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.
>
> Fix PERF_COUNT_SW_PAGE_FAULTS perf event manually for page fault retries, by
> moving it before taking mmap_sem.
>
> CC: Nick Hu <nickhu@...estech.com>
> CC: Greentime Hu <green.hu@...il.com>
> CC: Vincent Chen <deanbo422@...il.com>
> Signed-off-by: Peter Xu <peterx@...hat.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 only
>          * validly references user space from well defined areas of the code,
> @@ -207,7 +209,7 @@ void do_page_fault(unsigned long entry, unsigned long addr,
>          * the fault.
>          */
>
> -       fault = handle_mm_fault(vma, addr, flags, NULL);
> +       fault = 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 long 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 |= FAULT_FLAG_TRIED;
>

Hi Peter,

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