From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Date: Wed, 29 May 2024 14:59:55 -0700 Subject: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging In-Reply-To: References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-3-jthoughton@google.com> Message-ID: List-Id: To: kvm-riscv@lists.infradead.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, May 29, 2024, Yu Zhao wrote: > On Wed, May 29, 2024 at 12:05?PM James Houghton wrote: > > > > Secondary MMUs are currently consulted for access/age information at > > eviction time, but before then, we don't get accurate age information. > > That is, pages that are mostly accessed through a secondary MMU (like > > guest memory, used by KVM) will always just proceed down to the oldest > > generation, and then at eviction time, if KVM reports the page to be > > young, the page will be activated/promoted back to the youngest > > generation. > > Correct, and as I explained offline, this is the only reasonable > behavior if we can't locklessly walk secondary MMUs. > > Just for the record, the (crude) analogy I used was: > Imagine a large room with many bills ($1, $5, $10, ...) on the floor, > but you are only allowed to pick up 10 of them (and put them in your > pocket). A smart move would be to survey the room *first and then* > pick up the largest ones. But if you are carrying a 500 lbs backpack, > you would just want to pick up whichever that's in front of you rather > than walk the entire room. > > MGLRU should only scan (or lookaround) secondary MMUs if it can be > done lockless. Otherwise, it should just fall back to the existing > approach, which existed in previous versions but is removed in this > version. IIUC, by "existing approach" you mean completely ignore secondary MMUs that don't implement a lockless walk? 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charset="utf-8" Content-Transfer-Encoding: quoted-printable On Wed, May 29, 2024, Yu Zhao wrote: > On Wed, May 29, 2024 at 12:05=E2=80=AFPM James Houghton wrote: > > > > Secondary MMUs are currently consulted for access/age information at > > eviction time, but before then, we don't get accurate age information. > > That is, pages that are mostly accessed through a secondary MMU (like > > guest memory, used by KVM) will always just proceed down to the oldest > > generation, and then at eviction time, if KVM reports the page to be > > young, the page will be activated/promoted back to the youngest > > generation. >=20 > Correct, and as I explained offline, this is the only reasonable > behavior if we can't locklessly walk secondary MMUs. >=20 > Just for the record, the (crude) analogy I used was: > Imagine a large room with many bills ($1, $5, $10, ...) on the floor, > but you are only allowed to pick up 10 of them (and put them in your > pocket). A smart move would be to survey the room *first and then* > pick up the largest ones. But if you are carrying a 500 lbs backpack, > you would just want to pick up whichever that's in front of you rather > than walk the entire room. >=20 > MGLRU should only scan (or lookaround) secondary MMUs if it can be > done lockless. Otherwise, it should just fall back to the existing > approach, which existed in previous versions but is removed in this > version. IIUC, by "existing approach" you mean completely ignore secondary MMUs that= don't implement a lockless walk? 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Wed, 29 May 2024 14:59:56 -0700 (PDT) Date: Wed, 29 May 2024 14:59:55 -0700 In-Reply-To: Mime-Version: 1.0 References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-3-jthoughton@google.com> Message-ID: Subject: Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging From: Sean Christopherson To: Yu Zhao Cc: James Houghton , Andrew Morton , Paolo Bonzini , Albert Ou , Ankit Agrawal , Anup Patel , Atish Patra , Axel Rasmussen , Bibo Mao , Catalin Marinas , David Matlack , David Rientjes , Huacai Chen , James Morse , Jonathan Corbet , Marc Zyngier , Michael Ellerman , Nicholas Piggin , Oliver Upton , Palmer Dabbelt , Paul Walmsley , Raghavendra Rao Ananta , Ryan Roberts , Shaoqin Huang , Shuah Khan , Suzuki K Poulose , Tianrui Zhao , Will Deacon , Zenghui Yu , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240529_150002_330890_7CB3B78F X-CRM114-Status: GOOD ( 18.58 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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Wed, 29 May 2024 14:59:56 -0700 (PDT) Date: Wed, 29 May 2024 14:59:55 -0700 In-Reply-To: Mime-Version: 1.0 References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-3-jthoughton@google.com> Message-ID: Subject: Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging From: Sean Christopherson To: Yu Zhao Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: James Houghton , kvm@vger.kernel.org, linux-doc@vger.kernel.org, Catalin Marinas , Atish Patra , linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org, Raghavendra Rao Ananta , linux-riscv@lists.infradead.org, Shuah Khan , Jonathan Corbet , Anup Patel , Huacai Chen , David Rientjes , Zenghui Yu , Axel Rasmussen , linux-mips@vger.kernel.org, Albert Ou , Ryan Roberts , Will Deacon , Suzuki K Poulose , Shaoqin Huang , Nicholas Piggin , Bibo Mao , loongarch@lists.linux.dev, Paul Walmsley , David Matlack , Palmer Dabbelt , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, Ankit Agrawal , Oliver Upton , James Morse , kvm-riscv@lists.infradead.org, Marc Zyngier , Paolo Bonzini , Andrew Morton , Tianrui Zhao , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, May 29, 2024, Yu Zhao wrote: > On Wed, May 29, 2024 at 12:05=E2=80=AFPM James Houghton wrote: > > > > Secondary MMUs are currently consulted for access/age information at > > eviction time, but before then, we don't get accurate age information. > > That is, pages that are mostly accessed through a secondary MMU (like > > guest memory, used by KVM) will always just proceed down to the oldest > > generation, and then at eviction time, if KVM reports the page to be > > young, the page will be activated/promoted back to the youngest > > generation. >=20 > Correct, and as I explained offline, this is the only reasonable > behavior if we can't locklessly walk secondary MMUs. >=20 > Just for the record, the (crude) analogy I used was: > Imagine a large room with many bills ($1, $5, $10, ...) on the floor, > but you are only allowed to pick up 10 of them (and put them in your > pocket). A smart move would be to survey the room *first and then* > pick up the largest ones. But if you are carrying a 500 lbs backpack, > you would just want to pick up whichever that's in front of you rather > than walk the entire room. >=20 > MGLRU should only scan (or lookaround) secondary MMUs if it can be > done lockless. Otherwise, it should just fall back to the existing > approach, which existed in previous versions but is removed in this > version. IIUC, by "existing approach" you mean completely ignore secondary MMUs that= don't implement a lockless walk? 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Wed, 29 May 2024 14:59:56 -0700 (PDT) Date: Wed, 29 May 2024 14:59:55 -0700 In-Reply-To: Mime-Version: 1.0 References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-3-jthoughton@google.com> Message-ID: Subject: Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging From: Sean Christopherson To: Yu Zhao Cc: James Houghton , Andrew Morton , Paolo Bonzini , Albert Ou , Ankit Agrawal , Anup Patel , Atish Patra , Axel Rasmussen , Bibo Mao , Catalin Marinas , David Matlack , David Rientjes , Huacai Chen , James Morse , Jonathan Corbet , Marc Zyngier , Michael Ellerman , Nicholas Piggin , Oliver Upton , Palmer Dabbelt , Paul Walmsley , Raghavendra Rao Ananta , Ryan Roberts , Shaoqin Huang , Shuah Khan , Suzuki K Poulose , Tianrui Zhao , Will Deacon , Zenghui Yu , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240529_150002_115803_7D07FD2B X-CRM114-Status: GOOD ( 19.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org T24gV2VkLCBNYXkgMjksIDIwMjQsIFl1IFpoYW8gd3JvdGU6Cj4gT24gV2VkLCBNYXkgMjksIDIw MjQgYXQgMTI6MDXigK9QTSBKYW1lcyBIb3VnaHRvbiA8anRob3VnaHRvbkBnb29nbGUuY29tPiB3 cm90ZToKPiA+Cj4gPiBTZWNvbmRhcnkgTU1VcyBhcmUgY3VycmVudGx5IGNvbnN1bHRlZCBmb3Ig YWNjZXNzL2FnZSBpbmZvcm1hdGlvbiBhdAo+ID4gZXZpY3Rpb24gdGltZSwgYnV0IGJlZm9yZSB0 aGVuLCB3ZSBkb24ndCBnZXQgYWNjdXJhdGUgYWdlIGluZm9ybWF0aW9uLgo+ID4gVGhhdCBpcywg cGFnZXMgdGhhdCBhcmUgbW9zdGx5IGFjY2Vzc2VkIHRocm91Z2ggYSBzZWNvbmRhcnkgTU1VIChs aWtlCj4gPiBndWVzdCBtZW1vcnksIHVzZWQgYnkgS1ZNKSB3aWxsIGFsd2F5cyBqdXN0IHByb2Nl ZWQgZG93biB0byB0aGUgb2xkZXN0Cj4gPiBnZW5lcmF0aW9uLCBhbmQgdGhlbiBhdCBldmljdGlv biB0aW1lLCBpZiBLVk0gcmVwb3J0cyB0aGUgcGFnZSB0byBiZQo+ID4geW91bmcsIHRoZSBwYWdl IHdpbGwgYmUgYWN0aXZhdGVkL3Byb21vdGVkIGJhY2sgdG8gdGhlIHlvdW5nZXN0Cj4gPiBnZW5l cmF0aW9uLgo+IAo+IENvcnJlY3QsIGFuZCBhcyBJIGV4cGxhaW5lZCBvZmZsaW5lLCB0aGlzIGlz IHRoZSBvbmx5IHJlYXNvbmFibGUKPiBiZWhhdmlvciBpZiB3ZSBjYW4ndCBsb2NrbGVzc2x5IHdh bGsgc2Vjb25kYXJ5IE1NVXMuCj4gCj4gSnVzdCBmb3IgdGhlIHJlY29yZCwgdGhlIChjcnVkZSkg YW5hbG9neSBJIHVzZWQgd2FzOgo+IEltYWdpbmUgYSBsYXJnZSByb29tIHdpdGggbWFueSBiaWxs cyAoJDEsICQ1LCAkMTAsIC4uLikgb24gdGhlIGZsb29yLAo+IGJ1dCB5b3UgYXJlIG9ubHkgYWxs b3dlZCB0byBwaWNrIHVwIDEwIG9mIHRoZW0gKGFuZCBwdXQgdGhlbSBpbiB5b3VyCj4gcG9ja2V0 KS4gQSBzbWFydCBtb3ZlIHdvdWxkIGJlIHRvIHN1cnZleSB0aGUgcm9vbSAqZmlyc3QgYW5kIHRo ZW4qCj4gcGljayB1cCB0aGUgbGFyZ2VzdCBvbmVzLiBCdXQgaWYgeW91IGFyZSBjYXJyeWluZyBh IDUwMCBsYnMgYmFja3BhY2ssCj4geW91IHdvdWxkIGp1c3Qgd2FudCB0byBwaWNrIHVwIHdoaWNo ZXZlciB0aGF0J3MgaW4gZnJvbnQgb2YgeW91IHJhdGhlcgo+IHRoYW4gd2FsayB0aGUgZW50aXJl IHJvb20uCj4gCj4gTUdMUlUgc2hvdWxkIG9ubHkgc2NhbiAob3IgbG9va2Fyb3VuZCkgc2Vjb25k YXJ5IE1NVXMgaWYgaXQgY2FuIGJlCj4gZG9uZSBsb2NrbGVzcy4gT3RoZXJ3aXNlLCBpdCBzaG91 bGQganVzdCBmYWxsIGJhY2sgdG8gdGhlIGV4aXN0aW5nCj4gYXBwcm9hY2gsIHdoaWNoIGV4aXN0 ZWQgaW4gcHJldmlvdXMgdmVyc2lvbnMgYnV0IGlzIHJlbW92ZWQgaW4gdGhpcwo+IHZlcnNpb24u CgpJSVVDLCBieSAiZXhpc3RpbmcgYXBwcm9hY2giIHlvdSBtZWFuIGNvbXBsZXRlbHkgaWdub3Jl IHNlY29uZGFyeSBNTVVzIHRoYXQgZG9uJ3QKaW1wbGVtZW50IGEgbG9ja2xlc3Mgd2Fsaz8KCl9f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmxpbnV4LWFybS1r ZXJuZWwgbWFpbGluZyBsaXN0CmxpbnV4LWFybS1rZXJuZWxAbGlzdHMuaW5mcmFkZWFkLm9yZwpo dHRwOi8vbGlzdHMuaW5mcmFkZWFkLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2xpbnV4LWFybS1rZXJu ZWwK