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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 14 Jun 2021 07:58:07 -0700
Message-ID: <CAHk-=wg+TcJtrwEUzoht2j0R3+jw=OCqckptdf4Q9vNgCPSpXA@mail.gmail.com>
Subject: Re: [mm/mremap] ecf8443e51: vm-scalability.throughput -29.4% regression
To:     kernel test robot <oliver.sang@intel.com>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        0day robot <lkp@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        "Huang, Ying" <ying.huang@intel.com>,
        Feng Tang <feng.tang@intel.com>,
        Zhengjun Xing <zhengjun.xing@linux.intel.com>,
        Linux-MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Kalesh Singh <kaleshsingh@google.com>,
        Nick Piggin <npiggin@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        "Kirill A . Shutemov" <kirill@shutemov.name>
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On Mon, Jun 14, 2021 at 7:39 AM kernel test robot <oliver.sang@intel.com> wrote:
>

> FYI, we noticed a -29.4% regression of vm-scalability.throughput due to commit:
> ecf8443e51a8 ("[PATCH v7 02/11] mm/mremap: Fix race between MOVE_PUD mremap and pageout")

Ouch.

I guess it's not a huge surprise, but that's a fairly large regression.

Probably because the pud lock is just one single lock ("No scalability
reason to split PUD locks yet").

What happens if pud_lockptr() were to do the same thing that pmd_lockptr() does?

                Linus