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 E10B6C433FE for ; Fri, 15 Apr 2022 23:49:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233089AbiDOXwW (ORCPT ); Fri, 15 Apr 2022 19:52:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229645AbiDOXwS (ORCPT ); Fri, 15 Apr 2022 19:52:18 -0400 Received: from mail-vs1-xe2a.google.com (mail-vs1-xe2a.google.com [IPv6:2607:f8b0:4864:20::e2a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6BEE42BB14 for ; Fri, 15 Apr 2022 16:49:47 -0700 (PDT) Received: by mail-vs1-xe2a.google.com with SMTP id i186so8127810vsc.9 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=ZjULt1cRQCvHJHE2uo7Jnyfyaaz3pBbQJ+oEDBHSXjQ/IcIPvwKE/P+v+tAKhJovYr QA1z9iZkvIC308AHC+CkVo6d5lVvQD/uCn0uWPSbT3oWUxom2vVeIrs8Pjk9+XprA6sl f7nASaCCjiwXUgoNfsf7sZAwp/pnjSWvzuEsnjCPxLcpKFGP5tZ0iKy98b5CPI6cCeGz 1W858d9rPjEmqau/11HI+ME+8oYfjeJgT7X2syWvpQ+WNHY2EdwGdbOPwhFXz29N+qVY nNIeQUZyrQ9gZftX8gulpthughPI3xUkTMgqgIZLUWomyeQ2i3OFsJ7gYESh+CB1TOw3 Qghw== X-Gm-Message-State: AOAM53372MmkHefMtXg0t/2PdroC2OVpzXMW3hB5BMDmkvijPT4dY2Nz tOG/dGQWKOtEZgfU6zfyiv05tXGZChuc5mH8jxrR4g== 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" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B277EC433F5 for ; Fri, 15 Apr 2022 23:50:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:Subject:Message-ID:Date:From: In-Reply-To:References:MIME-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=oAzPjhsZM3jggGpURSU7TFnIUgTo86OG7EE4yLwR/fU=; b=KH62+8rS9vYrcS BchDbWJ5rdJbNNVqdkUIFiVL8ewciSl7S7c1Vi2ea/acuVa846PoSYXSXr56QcaE/DwPK4eu4ZBLu 7AKI4i1fF+AKmMBXpOgcXIXTkzGS4nV7By+ZdBTNIqBwltf+uC7IL4rltBN1pHz/rpQgib+XLMMwI Dmk/ImGt1hxi8BxEIu/DjEjPktFC5ses5RkovmvQdTQu63iZmBrBQJYcjbcARBdthFRzE4BnQVRFH ZbHGXPy5JhuggwUo1AwNWMyo5Gf/byJ7c/y+GkzWG9s2pUPru/fbjYUeiTH0K2kaVxHEXSbcBaTOy XUQ/CB85usFJk7Y0coFw==; 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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=fqMyWh4NykhkF8+Yhs0jJIxQIkgBhGCBRi8rXqgErnnE3+veH0PZs5chBLoO/CY6Gq tDWpA2yLqCBidebONUEInppSuZBk946cBg+CsX3IWD7r4Oi8Jou9DBoZMt9txg+NcFZL 7c3cqupaEA0cRheqYgcyTPzbJjuEXnUqjN2/2P0AGCD9EvXOBTeCZl18/oE2WTgWXIUz A+opWKO2rKgrkOC3EC6otEfRAzzaqTwZV0k4RfasbLYVCMMEy+T8Pmypn4kWnQGFRR6M MdNlxAgkw1yJpURrddjgymuu4zXT/Lb3nuJmbyuS5WmTfh57pLRtTKM+WgHMDo33PJ+Z JsRg== X-Gm-Message-State: AOAM533Qk21w8COen9tX0WSuugBSwkzH+rs1wny5iR+SAiGCDa+aqt7a xR51BA/3i+hlJIpjG7aFiwZ3o6v4/75pmkFTuppv3g== 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220415_164948_319326_A467D3EA X-CRM114-Status: GOOD ( 19.42 ) 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="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel