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Mon, 01 Apr 2024 21:07:34 -0700 (PDT) MIME-Version: 1.0 References: <20240401232946.1837665-1-jthoughton@google.com> <20240401232946.1837665-7-jthoughton@google.com> In-Reply-To: <20240401232946.1837665-7-jthoughton@google.com> From: Yu Zhao Date: Tue, 2 Apr 2024 00:06:56 -0400 Message-ID: Subject: Re: [PATCH v3 6/7] KVM: arm64: Participate in bitmap-based PTE aging To: James Houghton Cc: Andrew Morton , Paolo Bonzini , David Matlack , Marc Zyngier , Oliver Upton , Sean Christopherson , Jonathan Corbet , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Shaoqin Huang , Gavin Shan , Ricardo Koller , Raghavendra Rao Ananta , Ryan Roberts , David Rientjes , Axel Rasmussen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: nd85xnn8kz8gp6qhp5u7t6usuccpg1tb X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0946140004 X-HE-Tag: 1712030855-64555 X-HE-Meta: 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 N06kJ2C1 Tc3XHq5dgBcBfReMrwjy4+MnozHbbiCI4VnkAeGclhK4PiP/b5WtqdIPTqABenAJ9rkLLL6P/z5MqydjeARUYBXikQifmvaL/VfrYbnDyugtLlpTavgUU4Scc/QWjNTb+/qukZ7W5pRLbOEtpExrtIhRAjtj21Z7RCI2OGQvxTkydNqMWQFYrMDfdOLrcONnz7/2s2lQHubfhD4vBtjOwQ4o8Tur8efI5G8+Gh4BQ7B3ZDObU6ozj9JaqXg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000014, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 1, 2024 at 7:30=E2=80=AFPM James Houghton wrote: > > Participate in bitmap-based aging while grabbing the KVM MMU lock for > reading. Ideally we wouldn't need to grab this lock at all, but that > would require a more intrustive and risky change. ^^^^^^^^^^ intrusive This sounds subjective -- I'd just present the challenges and let reviewers make their own judgements. > Also pass > KVM_PGTABLE_WALK_SHARED, as this software walker is safe to run in > parallel with other walkers. > > It is safe only to grab the KVM MMU lock for reading as the kvm_pgtable > is destroyed while holding the lock for writing, and freeing of the page > table pages is either done while holding the MMU lock for writing or > after an RCU grace period. > > When mkold =3D=3D false, record the young pages in the passed-in bitmap. > > When mkold =3D=3D true, only age the pages that need aging according to t= he > passed-in bitmap. > > Suggested-by: Yu Zhao Thanks but I did not suggest this. What I have in v2 is RCU based. I hope Oliver or someone else can help make that work. Otherwise we can just drop this for now and revisit later. (I have no problems with this patch if the Arm folks think the RCU-based version doesn't have a good ROI.)