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From: Oliver Upton To: Yu Zhao Subject: Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging Message-ID: References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-3-jthoughton@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT 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 , Anup Patel , Paul Walmsley , 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 , Marc Zyngier , 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, Atish Patra , David Matlack , Palmer Dabbelt , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, Sean Christopherson , Ankit Agrawal , James Morse , kvm-riscv@lists.infradead.org, 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 Fri, May 31, 2024 at 10:45:04AM -0600, Yu Zhao wrote: > On Fri, May 31, 2024 at 1:03 AM Oliver Upton wrote: > > > > On Fri, May 31, 2024 at 12:05:48AM -0600, Yu Zhao wrote: > > Let me add back what I said earlier: > > I'm not convinced, but it doesn't mean your point of view is > invalid. If you fully understand the implications of your design > choice and document them, I will not object. Thanks, I appreciate the sentiment. Hopefully we can align here. > > > All optimizations in v2 were measured step by step. Even that bitmap, > > > which might be considered overengineered, brought a readily > > > measuarable 4% improvement in memcached throughput on Altra Max > > > swapping to Optane: > > > > That's great, but taking an iterative approach to the problem allows > > the reviewers and maintainers to come to their own conclusions about > > each optimization independently. Squashing all of that together and > > posting the result doesn't allow for this. > > That's your methodology, which I respect: as I said I won't stand in your way. > > But mine is backed by data, please do respect that as well, Data is useful and expected for changes that aim to improve the performance of a system in one way or another. That is, after all, the sole intention of the work, no? What I'm also looking for is a controlled experiment, where a single independent variable (e.g. locking) can be evaluated against the baseline. All-or-nothing data has limited usefulness. > by doing what I asked: document your justifications. The justification for a series is against the upstream tree, not some out-of-tree stuff. The cover letter explicitly calls out the decision to simplify the patch series along with performance data I can reproduce on my own systems. This is a perfect example of how to contribute changes upstream. > > > What I don't think is acceptable is simplifying those optimizations > > > out without documenting your justifications (I would even call it a > > > design change, rather than simplification, from v3 to v4). > > > > No, sorry, there's nothing wrong with James' approach here. > > Sorry, are you saying "without documenting your justifications" is > nothing wrong? If so, please elaborate. As I mentioned above, the reasoning is adequately documented and the discussion that led to v4 is public. OTOH... > > The discussion that led to the design of v4 happened on list; you were > > on CC. The general consensus on the KVM side was that the bitmap was > > complicated and lacked independent justification. There was ample > > opportunity to voice your concerns before he spent the time on v4. > > Please re-read my previous emails -- I never object to the removal of > the bitmap or James' approach. > > And please stop making assumptions -- I did voice my concerns with > James privately. ^~~~~~~~~ If it happened in private then its no better than having said nothing at all. Please, keep the conversation on-list next time so we can iron out any disagreements there. Otherwise contributors are put in a *very* awkward situation of mediating the on- and off-list dialogue. > > You seriously cannot fault a contributor for respinning their work based > > on the provided feedback. > > Are you saying I faulted James for taking others' feedback? No. Sufficient justification is captured in the public review feedback + series cover letter. Your statement that the approach was changed without justification is unsubstantiated. > Also what do you think about the technical flaws and inaccurate > understandings I pointed out? You seem to have a strong opinion on > your iterate approach, but I hope you didn't choose to overlook the > real meat of this discussion. Serious question: are you not receiving my mail or something? I re-raised my question to you from ages ago about locking on the arm64 MMU. You didn't answer last time, I'd appreciate a reply this time around. Otherwise I couldn't be bothered about the color of the Kconfig bikeshed and don't have anything meaningful to add there. I think the three of you are trending in the right direction. -- Thanks, Oliver