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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 007EFC433F5 for ; Fri, 15 Apr 2022 23:31:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4FBEF6B0072; Fri, 15 Apr 2022 19:31:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4A9BF6B0073; Fri, 15 Apr 2022 19:31:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 348DF6B0074; Fri, 15 Apr 2022 19:31:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.27]) by kanga.kvack.org (Postfix) with ESMTP id 26ED26B0072 for ; Fri, 15 Apr 2022 19:31:38 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id DE0076144E for ; Fri, 15 Apr 2022 23:31:37 +0000 (UTC) X-FDA: 79360712634.06.D87B0AD Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf11.hostedemail.com (Postfix) with ESMTP id E81A540008 for ; Fri, 15 Apr 2022 23:31:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Maymh2MrV1jISeToWbYmaZRo07zKhpb63QtPmZTv7xg=; b=e6NCa/1p/FL935pR/uKS7VVL9i NxQnlxKWSJ+Ta17K4gYFWJzNJxaihd8RTbIG62Xl/cDePuFPsB30gWB0IcujU2gd2gfIoljv8kQWO a4vkc0OuVSydPevgNNt6rL2VgEbG29LDZ1FfJZ57cwqVmS5EKHamBYm8UIT3i5D8R9KlKtcVG+ble STvluOBWwYBbjHwrFiqkAnABEhloL7s/LtsDqOchuG+G1mM7EccYDiMhrFJe8oDuHSMfsmaQ8X2ZO ulDAhPZJC0uuEEiyM3RkXZI1CV+mIrNhruJHvBcWrbnL/74JsnfYmPNwQUGQEobNYpz1o7MRUgG+O UT4DzE+g==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nfVP8-00Gbuq-8e; Fri, 15 Apr 2022 23:31:06 +0000 Date: Sat, 16 Apr 2022 00:31:06 +0100 From: Matthew Wilcox To: Jesse Barnes Cc: Linus Torvalds , Yu Zhao , 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 , Johannes Weiner , Jonathan Corbet , 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: [page-reclaim] Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks Message-ID: References: <20220414185654.e7150bcbe859e0dd4b9c61af@linux-foundation.org> <20220415121521.764a88dda55ae8c676ad26b0@linux-foundation.org> <20220415143220.cc37b0b0a368ed2bf2a821f8@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E81A540008 X-Stat-Signature: g5a4n36jduhxfbwsh59iarz4xkcj787c Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="e6NCa/1p"; dmarc=none; spf=none (imf11.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-HE-Tag: 1650065496-951493 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 04:24:14PM -0700, Jesse Barnes wrote: > On Fri, Apr 15, 2022 at 4:04 PM Linus Torvalds > wrote: > > 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. > > Generally agreed, and not to belabor this relatively small issue, but in some > environments like cloud or managed client deployments, a crash can actually > be preferable so we can get a dump, reboot the machine, and get things going > again for the application or user, then debug offline. So having the > flexibility to > do that in those situations is helpful. And there, a full crash dump is better > than just a log report with the WARN info, since debugging may be easier with > all the kernel memory. But for those situations, don't you set panic_on_warn anyway?