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[79.242.63.228]) by smtp.gmail.com with ESMTPSA id n20sm904818wms.15.2021.09.09.01.56.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Sep 2021 01:56:55 -0700 (PDT) Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page To: John Hubbard , 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: David Hildenbrand Organization: Red Hat Message-ID: Date: Thu, 9 Sep 2021 10:56:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=amLvhMej; spf=none (imf30.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 87046E001980 X-Stat-Signature: dk6ncj4ghek3mksne1kn7qa33ioe5ma3 X-HE-Tag: 1631177819-913933 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 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. 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... -- Thanks, David / dhildenb