linux-kernel - Re: [PATCH mm-unstable v2 00/10] mm/kvm: locklessly clear the accessed bit

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Date:   Mon, 19 Jun 2023 20:19:11 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alistair Popple <apopple@...dia.com>,
        Anup Patel <anup@...infault.org>,
        Ben Gardon <bgardon@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Gaosheng Cui <cuigaosheng1@...wei.com>,
        Gavin Shan <gshan@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Marc Zyngier <maz@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Larabel <michael@...haellarabel.com>,
        Mike Rapoport <rppt@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Paul Mackerras <paulus@...abs.org>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thomas Huth <thuth@...hat.com>, Will Deacon <will@...nel.org>,
        Zenghui Yu <yuzenghui@...wei.com>, kvmarm@...ts.linux.dev,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-trace-kernel@...r.kernel.org, x86@...nel.org,
        linux-mm@...gle.com
Subject: Re: [PATCH mm-unstable v2 00/10] mm/kvm: locklessly clear the
 accessed bit

On Fri, Jun 9, 2023 at 3:08 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 5/27/23 01:44, Yu Zhao wrote:
> > TLDR
> > ====
> > This patchset adds a fast path to clear the accessed bit without
> > taking kvm->mmu_lock. It can significantly improve the performance of
> > guests when the host is under heavy memory pressure.
> >
> > ChromeOS has been using a similar approach [1] since mid 2021 and it
> > was proven successful on tens of millions devices.
> >
> > This v2 addressed previous requests [2] on refactoring code, removing
> > inaccurate/redundant texts, etc.
> >
> > [1]https://crrev.com/c/2987928
> > [2]https://lore.kernel.org/r/20230217041230.2417228-1-yuzhao@google.com/
>
>  From the KVM point of view the patches look good (though I wouldn't
> mind if Nicholas took a look at the ppc part).  Jason's comment on the
> MMU notifier side are promising as well.  Can you send v3 with Oliver's
> comments addressed?

Thanks. I'll address all the comments in v3 and post it asap.

Meanwhile, some updates on the recent progress from my side:
1. I've asked some downstream kernels to pick up v2 for testing, the
Archlinux Zen kernel did. I don't really expect its enthusiastic
testers to find this series relevant to their use cases. But who
knows.
2. I've also asked openbenchmarking.org to run their popular highmem
benchmark suites with v2. Hopefully they'll have some independent
results soon.
3. I've backported v2 to v5.15 and v6.1 and started an A/B experiment
involving ~1 million devices, as I mentioned in another email in this
thread. I should have some results to share when posting v3.