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d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=GBzN0oGFUFjzpywBXSVux/Xmu/oJE1kMpJ05D3WkT7w=; b=5aAB9XK+4SlhaD22nGO6tU+hqlbcMqbpVdds7kJIby2C8zlM586WqrLZNNCuScA4VM GOtG8CzWa0C6412GLdirxjolZ7D5Rf366OjVxrKTJOwhjQZEecVmSHHxxi8SGrBRX97+ /Ob4WVgRKe/ht6xHUhyzguVCb70Nvn3BIrgYfsEwHbIkbvlToVoMLfcaMZl1j2plD7HJ Up9Qq8VcMLDCgf1QFB4bewPZ+QnriaTrORAZJHKH7BC6D1pvnNAHWEpyDkv6sMZBd14c U6N3A0Vn1Rf0B4ufA441X5BLRSM4lD+M92qqOXk6xD1zzjU+m55olSFIuTdxEjd4JyQa GDRg== X-Gm-Message-State: AOAM533ZJyicmz252AFhzYCwaBBQ1mddImpOp/cQ3kV9B+sQpLqH017d TeRMQsm4nfZgTJPeoXwZ3a9LVu6kmj+S+s0qM5By1g== X-Google-Smtp-Source: ABdhPJyg4K4LACqH2AcGFF1qsZf4zXwnYa7M+1ZR/KBW0Gvu89HiGnqnLTcYYAIN5JZCFsJgUKCChcvn9V71cx1qJ0Y= X-Received: by 2002:a81:8b47:0:b0:2e6:57ba:5f84 with SMTP id e7-20020a818b47000000b002e657ba5f84mr1217410ywk.285.1650065849882; Fri, 15 Apr 2022 16:37:29 -0700 (PDT) MIME-Version: 1.0 References: <20220414185654.e7150bcbe859e0dd4b9c61af@linux-foundation.org> <20220415121521.764a88dda55ae8c676ad26b0@linux-foundation.org> <20220415143220.cc37b0b0a368ed2bf2a821f8@linux-foundation.org> In-Reply-To: From: Jesse Barnes Date: Fri, 15 Apr 2022 16:37:17 -0700 Message-ID: Subject: Re: [page-reclaim] Re: [PATCH v10 08/14] mm: multi-gen LRU: support page table walks To: Matthew Wilcox 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 , =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= , Konstantin Kharlamov , Shuang Zhai , Sofia Trinh , Vaibhav Jain Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=gEXUAF2g; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf20.hostedemail.com: domain of jsbarnes@google.com designates 209.85.128.169 as permitted sender) smtp.mailfrom=jsbarnes@google.com X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D89CD1C0005 X-Stat-Signature: 1fx3ybijjoms7r188nbayd5quuemukiq X-HE-Tag: 1650065850-870234 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, 4:31 PM Matthew Wilcox wrote: > > 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? Yes ignore me. Jesse "returning to his cave of ignorace" Barnes