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AJvYcCXBTCqQAVbEYcY6ciOgfS/fhJslKRrewg/Z4s+BBV183l64XTsUIzhZEFutHYW55cxyVWZzrjziOqxF36xxh6LTgl4= X-Gm-Message-State: AOJu0Yyu7lPLTMXcXZ+iI332cOoeLF7Y5ic8RGkHJaonuoN0xHpr+JVr 8uro+C18x5OcSEmtaJfUyfsNDCUW1Bv1K0xmzzCX5TZeJYz5Qdo45govSCeXFuHIPvRjMDtLZlo brNwoADfopNCL6zk/0O6G2Dah/BoSSaclGtA0 X-Google-Smtp-Source: AGHT+IFv1QNbGHT+roZmsKKDk+4PrHigHuJTamLsAWVaJCEFFb06VO4JQpFPHTrcY52wz67cbMD5ADs0MVUpOaV74QM= X-Received: by 2002:ac8:729a:0:b0:437:b99c:dbf7 with SMTP id v26-20020ac8729a000000b00437b99cdbf7mr13893qto.11.1713560259365; Fri, 19 Apr 2024 13:57:39 -0700 (PDT) MIME-Version: 1.0 References: <20240401232946.1837665-1-jthoughton@google.com> In-Reply-To: From: James Houghton Date: Fri, 19 Apr 2024 13:57:03 -0700 Message-ID: Subject: Re: [PATCH v3 0/7] mm/kvm: Improve parallelism for access bit harvesting To: David Matlack Cc: Andrew Morton , Paolo Bonzini , Yu Zhao , 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-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 562E7A0009 X-Rspam-User: X-Stat-Signature: cofr39sk7w1zsggmor64bsy4kszjkudp X-HE-Tag: 1713560260-489687 X-HE-Meta: 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 xlLZoKVR FQGe28XahCR+c/frS/2+wc+/IHvaq9J/XUj1UmWzRDOrKYZ0NVYVIqbB+YlT+xXWHBI8ZHxdypcp7G3EZDkkAdBnEMpOsouSpx6dN6Zplfqj/3olndV2TMJFog5bme0UMixNmV5tnSnTN1r6hnEkfTjx3FMgnTosnakDn86ZdZCiQSHLT4lvzdmoS9r1iBRJpnyTNsBLFZmOC9ZAhMBjBDzNtmFDMl6p7U6wTI3k1QnyTKGW0W6T9xHApgfwjg0ennp67HybDxuTIbpuvBgEP42uXPPdAq10Tq8VZkm/YeVJCHSA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Fri, Apr 12, 2024 at 11:41=E2=80=AFAM David Matlack wrote: > > On 2024-04-01 11:29 PM, James Houghton wrote: > > This patchset adds a fast path in KVM to test and clear access bits on > > sptes without taking the mmu_lock. It also adds support for using a > > bitmap to (1) test the access bits for many sptes in a single call to > > mmu_notifier_test_young, and to (2) clear the access bits for many ptes > > in a single call to mmu_notifier_clear_young. > > How much improvement would we get if we _just_ made test/clear_young > lockless on x86 and hold the read-lock on arm64? And then how much > benefit does the bitmap look-around add on top of that? I don't have these results right now. For the next version I will (1) separate the series into the locking change and the bitmap change, and I will (2) have performance data for each change separately. It is conceivable that the bitmap change should just be considered as a completely separate patchset.