linux-kernel - Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging

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Date: Mon, 3 Jun 2024 17:23:06 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: James Houghton <jthoughton@...gle.com>
Cc: Yu Zhao <yuzhao@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Paolo Bonzini <pbonzini@...hat.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Ankit Agrawal <ankita@...dia.com>, Anup Patel <anup@...infault.org>, 
	Atish Patra <atishp@...shpatra.org>, Axel Rasmussen <axelrasmussen@...gle.com>, 
	Bibo Mao <maobibo@...ngson.cn>, Catalin Marinas <catalin.marinas@....com>, 
	David Matlack <dmatlack@...gle.com>, David Rientjes <rientjes@...gle.com>, 
	Huacai Chen <chenhuacai@...nel.org>, James Morse <james.morse@....com>, 
	Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>, Michael Ellerman <mpe@...erman.id.au>, 
	Nicholas Piggin <npiggin@...il.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Raghavendra Rao Ananta <rananta@...gle.com>, Ryan Roberts <ryan.roberts@....com>, 
	Shaoqin Huang <shahuang@...hat.com>, Shuah Khan <shuah@...nel.org>, 
	Suzuki K Poulose <suzuki.poulose@....com>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	Will Deacon <will@...nel.org>, Zenghui Yu <yuzenghui@...wei.com>, kvm-riscv@...ts.infradead.org, 
	kvm@...r.kernel.org, kvmarm@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-mips@...r.kernel.org, linux-mm@...ck.org, 
	linux-riscv@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org, 
	loongarch@...ts.linux.dev
Subject: Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate
 in aging

On Mon, Jun 03, 2024, James Houghton wrote:
> On Mon, Jun 3, 2024 at 4:03 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > But before we do that, I think we need to perform due dilegence (or provide data)
> > showing that having KVM take mmu_lock for write in the "fast only" API provides
> > better total behavior.  I.e. that the additional accuracy is indeed worth the cost.
> 
> That sounds good to me. I'll drop the Kconfig. I'm not really sure
> what to do about the self-test, but that's not really all that
> important.

Enable it only on architectures+setups that are guaranteed to implement the
fast-only API?  E.g. on x86, it darn well better be active if the TDP MMU is
enabled.  If the test fails because that doesn't hold true, then we _want_ the
failure.