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[209.85.221.49]) by smtp.gmail.com with ESMTPSA id bn14-20020a170906c0ce00b006c5ef0494besm102994ejb.86.2022.03.08.16.30.00 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Mar 2022 16:30:00 -0800 (PST) Received: by mail-wr1-f49.google.com with SMTP id u1so575262wrg.11 for ; Tue, 08 Mar 2022 16:30:00 -0800 (PST) X-Received: by 2002:ac2:44a4:0:b0:445:8fc5:a12a with SMTP id c4-20020ac244a4000000b004458fc5a12amr12499712lfm.27.1646785789558; Tue, 08 Mar 2022 16:29:49 -0800 (PST) MIME-Version: 1.0 References: <20220308234723.3834941-1-yuzhao@google.com> In-Reply-To: From: Linus Torvalds Date: Tue, 8 Mar 2022 16:29:33 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v8 00/14] Multi-Gen LRU Framework To: Yu Zhao Cc: Andrew Morton , Andi Kleen , Aneesh Kumar , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Michal Hocko , Mike Rapoport , Rik van Riel , Vlastimil Babka , Will Deacon , Ying Huang , Linux ARM , "open list:DOCUMENTATION" , Linux Kernel Mailing List , Linux-MM , Kernel Page Reclaim v2 , "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1DBC940003 X-Stat-Signature: hbexhko7s94p1ye8hzkzbfngera9czbm Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=fk9Kkf3U; spf=pass (imf04.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.218.48 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-HE-Tag: 1646785801-659555 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: On Tue, Mar 8, 2022 at 4:15 PM Yu Zhao wrote: > > This sounds self-serving: our data centers want them, so I had to try. Heh. I'm not opposed to putting them back in, but if/when we merge the multi-gen LRU code, I really want people to be all testing the same thing. I also think that if we put them back in, that should come with (a) performance numbers for the different cases (b) hard guidance of what the numbers should be, and under what circumstances (ie giving the user enough information that he *can* answer the question for his configuration) (c) some thought about perhaps making them possibly more dynamic than a hardcoded build-time value (assuming the numbers show that it's worth doing in the first place, of course) so I think that the support for the concept can/should be left in, but I think that kind of fancy "I want more generations or fewer tiers-per-generation because of XYZ" needs to be a separate issue with more explanation from the initial "This multi-gen LRU gives better performance" merge. Because as-is, I don't think those config options had nearly enough information associated with them to merit them existing. Linus