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Thu, 9 Sep 2021 16:50:39 +0000 Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page To: David Hildenbrand , Vlastimil Babka , Miaohe Lin , akpm@linux-foundation.org Cc: iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210904091839.20270-1-linmiaohe@huawei.com> <3b36529f-ab97-ddfe-0407-66f0cd1fd38d@redhat.com> <2d06db75-5c26-8fe2-6883-ac99056a9894@redhat.com> <80cfffdc-227e-c045-be74-1c08fb62c1e3@redhat.com> From: John Hubbard Message-ID: <88bcab16-b248-3cdd-1270-1f162f43019f@nvidia.com> Date: Thu, 9 Sep 2021 09:50:38 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR07CA0052.namprd07.prod.outlook.com (2603:10b6:a03:60::29) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 Received: from [10.2.63.205] (216.228.112.22) by BYAPR07CA0052.namprd07.prod.outlook.com (2603:10b6:a03:60::29) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4500.14 via Frontend Transport; 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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=F2GloDs4; spf=none (imf04.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.236.44) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (policy=quarantine) header.from=nvidia.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 01FC250000A6 X-Stat-Signature: t8fb16yn3dxngrs34yf4g8m7kb7iyhfo X-HE-Tag: 1631206240-360873 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 9/9/21 1:56 AM, David Hildenbrand wrote: > On 09.09.21 00:42, John Hubbard wrote: >> On 9/7/21 2:56 AM, David Hildenbrand wrote: >> ... >>>> If this can be handled gracefully, then I'd rather go with VM_WARN_ON. >>>> Maybe even WARN_ON_ONCE? >>>> >>> >>> I think either VM_BUG_ON() or VM_WARN_ON() -- compiling the runtime checks out -- should be good >>> enough. >>> >>> I'd just go with VM_BUG_ON(), because anybody messing with __isolate_free_page() should clearly spot >>> that we expect the current handling. But no strong opinion. >>> >> >> If in doubt, WARN*() should be preferred over BUG*(). There's a pretty long >> history of "don't kill the machine unless you have to" emails about this, let >> me dig up one...OK, maybe not the best example, but the tip of the iceberg: > > Please note the subtle difference between BUG_ON and VM_BUG_ON. We expect VM_BUG_ON to be compiled > out on any production system. So it's really only a mean to identify things that really shouldn't be > like that during debugging/testing. > Yes, but the end result is the same: it halts the system. It don't think it changes the reasoning about BUG vs WARN very much. > Using WARN... instead of VM_BUG_ON is even worse for production systems. There are distros that set > panic_on_warn, essentially converting WARN... into BUG... > This is different than BUG: panic() *prints a backtrace*, and then reboots the system. That is still awkward, but a little more debuggable. thanks, -- John Hubbard NVIDIA