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Fri, 15 Apr 2022 23:49:47 +0000 (UTC) X-FDA: 79360758414.17.34289A9 Received: from mail-vs1-f46.google.com (mail-vs1-f46.google.com [209.85.217.46]) by imf16.hostedemail.com (Postfix) with ESMTP id 46A13180005 for ; Fri, 15 Apr 2022 23:49:47 +0000 (UTC) Received: by mail-vs1-f46.google.com with SMTP id v133so4602513vsv.7 for ; Fri, 15 Apr 2022 16:49:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Qr6XNF1bK3PdePl03u0gY6aVL4clB778VuHLiEk7Bus=; b=lf2+gHgcE6Sjq8PQbV9FP6YTAFbqNAhZzALie/K0UJSwp8Oa59xE5fwxN11DNM1jzF F3nCS/VDmcRfjfl+JURbhT1QwWlvTf6TMOvYedmPUuhYHZoZ3FWE5qDqrpcgiKwp2M5b jIKbKuIKL6O8SCdu+Nkg0t7A2o9CszAGzTa03ecBG4fd70UaiXXatm8yPzcBm+xkUc0w OlyD+/B7EBheiPusiGgfwCmbaSrnOrKXiajcUq9uILobC5vaoL8BOyYShHP5yPjJ3eKX +ZcE5PfQI7fVU5JbPATy7K69qjCUTJycQkXpbAtC/uy29svtVfrMRlXv8Zkh0xmeSuTJ tKrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Qr6XNF1bK3PdePl03u0gY6aVL4clB778VuHLiEk7Bus=; b=sX7xFMK/7VAyhn6NERKAE05wzUfuto759aptw0AqKzw6tSsx87p6RYoYOo1QSrui0y NmfNbko3+WkYf0pHacupvxFoGZ9gzjRoKsfPAqTaoTZ1PmKdjHrNje3RBAda466mxo8H V33ff+EANOz3El6VfhXFTUWURFyQZH5GZ4dTiLOPSmBZ7QSOatXSgvsFuT6QC0bZiyVs Hxan36+yMSalsEZXre5X3TygbPzAXLkI0GsdFMtYhkTuwqdXRqvOqyU5MR+QA/C62M/n KTocNBTCsh1yE8Ave1bNnyojtb/nBXT9tkUq7UySlZAw+qLk50fWrrMx7lho0TukybVa Rt9Q== X-Gm-Message-State: AOAM533p3UhkjBK6zIBHgbN4S/G2XJGhOuHaUQKq8Y1YED9eGcDFkRsZ bWVGDrun2Jbx/qLqGQtexhwq7iucZFi9NrUlBWPasA== X-Google-Smtp-Source: ABdhPJyW7+XQXBJpdsz4McEx26yYkMLlsqpGPfU1l0p0386BmKCCX+y/uTbiRr+7GHVmV1rMDNlghHYJg9Cw/My3+7o= X-Received: by 2002:a05:6102:3753:b0:325:c20e:4b1c with SMTP id u19-20020a056102375300b00325c20e4b1cmr361726vst.84.1650066586474; Fri, 15 Apr 2022 16:49:46 -0700 (PDT) MIME-Version: 1.0 References: <20220407031525.2368067-1-yuzhao@google.com> <20220407031525.2368067-9-yuzhao@google.com> <20220411191621.0378467ad99ebc822d5ad005@linux-foundation.org> <20220414185654.e7150bcbe859e0dd4b9c61af@linux-foundation.org> <20220415121521.764a88dda55ae8c676ad26b0@linux-foundation.org> <20220415143220.cc37b0b0a368ed2bf2a821f8@linux-foundation.org> In-Reply-To: From: Yu Zhao Date: Fri, 15 Apr 2022 17:49:09 -0600 Message-ID: Subject: Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks To: Linus Torvalds Cc: Andrew Morton , Justin Forbes , 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 , 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 , =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 46A13180005 X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=lf2+gHgc; spf=pass (imf16.hostedemail.com: domain of yuzhao@google.com designates 209.85.217.46 as permitted sender) smtp.mailfrom=yuzhao@google.com; dmarc=pass (policy=reject) header.from=google.com X-Stat-Signature: srxx6rkcgrye57msy9t69uubnowfpm3q X-HE-Tag: 1650066587-767856 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 Fri, Apr 15, 2022 at 5:03 PM Linus Torvalds wrote: > > On Fri, Apr 15, 2022 at 3:58 PM Yu Zhao wrote: > > > > BUG_ONs are harmful but problems that trigger them would be > > presummingly less penetrating to the user base; on the other hand, > > from my experience working with some testers (ordinary users), they > > ignore WARN_ON_ONCEs until the kernel crashes. > > I don't understand your argument. > > First you say that VM_BUG_ON() is only for VM developers. I did? Probably I implied CONFIG_DEBUG_VM=y is meant for MM developers. > Then you say "some testers (ordinary users) ignore WARN_ON_ONCEs until > the kernel crashes". > > So which is it? > > VM developers, or ordinary users? Ordinary users. > Honestly, if a VM developer is ignoring a WARN_ON_ONCE() from the VM > subsystem, I don't even know what to say. Same here. I wasn't worried about kernel developers ignoring any warnings. > And for ordinary users, a WARN_ON_ONCE() is about a million times > better, becasue: > > - the machine will hopefully continue working, so they can report the warning > > - even when they don't notice them, distros tend to have automated > reporting infrastructure > > That's why I absolutely *DETEST* those stupid BUG_ON() cases - they > will often kill the machine with nasty locks held, resulting in a > completely undebuggable thing that never gets reported. > > Yes, you can be careful and only put BUG_ON() in places where recovery > is possible. But even then, they have no actual _advantages_ over just > a WARN_ON_ONCE. I hear you, and I wasn't arguing about anything, just sharing my two cents.