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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Xu <peterx@redhat.com>
Cc: Guo Ren <guoren@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Gerald Schaefer <gerald.schaefer@de.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-csky@vger.kernel.org
Subject: Re: [PATCH 07/25] mm/csky: Use mm_fault_accounting()
Date: Thu, 18 Jun 2020 10:15:50 -0700	[thread overview]
Message-ID: <CAHk-=whFEZbTJZaNwEkyevUV2aqRwbeVmtp6hhk1sK2mW4vaGA@mail.gmail.com> (raw)
In-Reply-To: <20200618143801.GK76766@xz-x1>

On Thu, Jun 18, 2020 at 7:38 AM Peter Xu <peterx@redhat.com> wrote:
>
> GUP needs the per-task accounting, but not the perf events.  We can do that by
> slightly changing the new approach into:
>
>         bool major = (ret & VM_FAULT_MAJOR) || (flags & FAULT_FLAG_TRIED);
>
>         if (major)
>                 current->maj_flt++;
>         else
>                 current->min_flt++;
>
>         if (!regs)
>                 return ret;
>
>         if (major)
>                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
>         else
>                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);

Ack, I think this is the right thing to do.

No normal situation will ever notice the difference, with remote
accesses being as rare and specialized as they are. But being able to
remote the otherwise unused 'tsk' parameter sounds like the right
thing to do too.

It might be worth adding a comment about why.

Also, honestly, how about we remove the 'major' variable entirely, and
instead make the code be something like

        unsigned long *flt;
        int event_type;
        ...

        /* Major fault */
        if ((ret & VM_FAULT_MAJOR) || (flags & FAULT_FLAG_TRIED)) {
                flt = &current->maj_flt;
                event_type = PERF_COUNT_SW_PAGE_FAULTS_MAJ;
        } else {
                flt = &current->min_flt;
                event_type = PERF_COUNT_SW_PAGE_FAULTS_MIN;
        }
        *flt++;
        if (regs)
                perf_sw_event(event_type, 1, regs, address);

instead. Less source code duplication, and I bet it improves code
generation too.

             Linus

  reply	other threads:[~2020-06-18 17:16 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-15 22:15 [PATCH 00/25] mm: Page fault accounting cleanups Peter Xu
2020-06-15 22:15 ` [PATCH 01/25] mm/um: Fix extra accounting for page fault retries Peter Xu
2020-06-15 22:15 ` [PATCH 02/25] mm: Introduce mm_fault_accounting() Peter Xu
2020-06-15 22:32   ` Linus Torvalds
2020-06-15 23:19     ` Peter Xu
2020-06-16 19:00       ` Andrew Morton
2020-06-17 16:26         ` Peter Xu
2020-06-15 22:15 ` [PATCH 03/25] mm/alpha: Use mm_fault_accounting() Peter Xu
2020-06-15 22:15 ` [PATCH 04/25] mm/arc: " Peter Xu
2020-06-15 22:15 ` [PATCH 05/25] mm/arm: " Peter Xu
2020-06-15 22:15 ` [PATCH 06/25] mm/arm64: " Peter Xu
2020-06-16  7:43   ` Will Deacon
2020-06-16 15:59     ` Peter Xu
2020-06-15 22:15 ` [PATCH 07/25] mm/csky: " Peter Xu
2020-06-17  7:04   ` Guo Ren
2020-06-17 15:49     ` Peter Xu
2020-06-17 17:53       ` Linus Torvalds
2020-06-17 19:58         ` Peter Xu
2020-06-17 20:15           ` Linus Torvalds
2020-06-18 14:38             ` Peter Xu
2020-06-18 17:15               ` Linus Torvalds [this message]
2020-06-18 21:24                 ` Peter Xu
2020-06-18 22:28                   ` Peter Xu
2020-06-18 22:59                     ` Linus Torvalds
2020-06-15 22:15 ` [PATCH 08/25] mm/hexagon: " Peter Xu
2020-06-15 22:15 ` [PATCH 09/25] mm/ia64: " Peter Xu
2020-06-15 22:15 ` [PATCH 10/25] mm/m68k: " Peter Xu
2020-06-15 22:15 ` [PATCH 11/25] mm/microblaze: " Peter Xu
2020-06-15 22:15 ` [PATCH 12/25] mm/mips: " Peter Xu
2020-06-15 22:15 ` [PATCH 13/25] mm/nds32: " Peter Xu
2020-06-17  1:05   ` Greentime Hu
2020-06-15 22:15 ` [PATCH 14/25] mm/nios2: " Peter Xu
2020-06-15 22:15 ` [PATCH 15/25] mm/openrisc: " Peter Xu
2020-06-16 18:11   ` Stafford Horne
2020-06-15 22:15 ` [PATCH 16/25] mm/parisc: " Peter Xu
2020-06-15 22:15 ` [PATCH 17/25] mm/powerpc: " Peter Xu
2020-06-15 22:16 ` [PATCH 18/25] mm/riscv: " Peter Xu
2020-06-18 23:49   ` Palmer Dabbelt
2020-06-19  0:12     ` Peter Xu
2020-06-15 22:23 ` [PATCH 19/25] mm/s390: " Peter Xu
2020-06-16 15:59   ` Alexander Gordeev
2020-06-16 16:35     ` Peter Xu
2020-06-17  6:19       ` Christian Borntraeger
2020-06-17 16:06         ` Peter Xu
2020-06-17 16:14           ` Christian Borntraeger
2020-06-17 16:44             ` Peter Xu
2020-06-15 22:23 ` [PATCH 20/25] mm/sh: " Peter Xu
2020-07-20 21:25   ` Rich Felker
2020-07-20 22:05     ` Peter Xu
2020-06-15 22:23 ` [PATCH 21/25] mm/sparc32: " Peter Xu
2020-06-15 22:23 ` [PATCH 22/25] mm/sparc64: " Peter Xu
2020-06-15 22:23 ` [PATCH 23/25] mm/unicore32: " Peter Xu
2020-06-15 22:23 ` [PATCH 24/25] mm/x86: " Peter Xu
2020-06-15 22:23 ` [PATCH 25/25] mm/xtensa: " Peter Xu
2020-06-15 23:13   ` Max Filippov
2020-06-16 18:55 ` [PATCH 00/25] mm: Page fault accounting cleanups Linus Torvalds
2020-06-16 21:03   ` Peter Xu
2020-06-17  0:55   ` Michael Ellerman
2020-06-17  8:04     ` Will Deacon
2020-06-17 16:10       ` Peter Xu

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