From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2F57CC433F5 for ; Tue, 26 Apr 2022 21:30:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355424AbiDZVdv (ORCPT ); Tue, 26 Apr 2022 17:33:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351728AbiDZVdr (ORCPT ); Tue, 26 Apr 2022 17:33:47 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 727B2167D1; Tue, 26 Apr 2022 14:30:37 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 0864661768; Tue, 26 Apr 2022 21:30:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B698C385A0; Tue, 26 Apr 2022 21:30:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1651008636; bh=hRBN2iGUWntk6rFDQClPrjJSN1u3Plq5R5MkMdlntzA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=2AgeVAJdYeuPtwz5M/eqMKQsJKokdP1kIZVf0URVWM3SGYun4iiEJslJB0++i7lv+ G29Uwsy2kwANU1AUg4BAnaWWNz9Q1s5uGgVhQoLMY6hwbuitH9tHnUinZbWz/b/lia ThO4ZAVemknNsB+RzsmXUH8bOCELau56862WiyuQ= Date: Tue, 26 Apr 2022 14:30:34 -0700 From: Andrew Morton To: Yu Zhao Cc: Stephen Rothwell , Linux-MM , Andi Kleen , Aneesh Kumar , Barry Song <21cnbao@gmail.com>, Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Linus Torvalds , 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 , Kernel Page Reclaim v2 , "the arch/x86 maintainers" , Brian Geffon , Jan Alexander Steffens , Oleksandr Natalenko , Steven Barrett , Suleiman Souhlal , Daniel Byrne , Donald Carr , Holger =?ISO-8859-1?Q?Hoffst=E4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain Subject: Re: [PATCH v10 12/14] mm: multi-gen LRU: debugfs interface Message-Id: <20220426143034.f520c062830f9e3405c890d0@linux-foundation.org> In-Reply-To: References: <20220407031525.2368067-1-yuzhao@google.com> <20220407031525.2368067-13-yuzhao@google.com> <20220411191634.674554d3de2ba37b3db40ca2@linux-foundation.org> <20220415212024.c682ac000e3e91572d8d6d2b@linux-foundation.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, 26 Apr 2022 00:59:37 -0600 Yu Zhao wrote: > On Fri, Apr 15, 2022 at 10:20 PM Andrew Morton > wrote: > > > > On Fri, 15 Apr 2022 18:03:16 -0600 Yu Zhao wrote: > > > > > > Presumably sysfs is the place. Fully documented and with usage > > > > examples in the changelog so we can carefully review the proposed > > > > extensions to Linux's ABI. Extensions which must be maintained > > > > unchanged for all time. > > > > > > Eventually, yes. There still is a long way to go. Rest assured, this > > > is something Google will keep investing resources on. > > > > So. The plan is to put these interfaces in debugfs for now, with a > > view to migrating stabilized interfaces into sysfs (or procfs or > > whatever) once end-user requirements and use cases are better > > understood? > > The requirements are well understood and the use cases are proven, > e.g., Google [1], Meta [2] and Alibaba [3]. > > [1] https://dl.acm.org/doi/10.1145/3297858.3304053 > [2] https://dl.acm.org/doi/10.1145/3503222.3507731 > [3] https://gitee.com/anolis/cloud-kernel/blob/release-5.10/mm/kidled.c So will these interfaces be moved into sysfs? > > If so, that sounds totally great to me. But it should have been in > > the darn changelog! This is the sort of thing which we care about most > > keenly. > > > > It would be helpful for reviewers to understand the proposed timeline > > for this process, because the entire feature isn't really real until > > this is completed, is it? I do think we should get this nailed down > > relatively rapidly, otherwise people will be reluctant to invest much > > into a moving target. > > > > And I must say, I see dissonance between the overall maturity of the > > feature as described in these emails versus the immaturity of these > > userspace control interfaces. What's happening there? > > Very observant. To answer both of the questions above: each iteration > of the entire stack is a multi-year effort. > > Given its ROI, companies I know of constantly pour money into this > area. Given its scale, this debugfs is the least of their concerns. A > good example is the proactive reclaim sysfs interface [4]. It's been > used at Google for many years and at Meta for a few years. We only > started finalizing it recently. > > [4] https://lore.kernel.org/r/20220425190040.2475377-1-yosryahmed@google.com/ Sure, if one organization is involved in both the userspace code and the kernel interfaces then the alteration of kernel interfaces can be handled in a coordinated fashion. But releasing interfaces to the whole world is a different deal. It's acceptable to say "this is in debugfs for now because it's a work in progress" but it sounds like mglru's interfaces are beyond that stage?