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[79.242.63.228]) by smtp.gmail.com with ESMTPSA id a10sm1250078wrd.51.2021.09.09.02.37.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Sep 2021 02:37:26 -0700 (PDT) To: Vlastimil Babka , John Hubbard , 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 Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page Message-ID: <924b4672-0e52-56fb-22a9-b02d8c3ecccf@redhat.com> Date: Thu, 9 Sep 2021 11:37:26 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09.09.21 11:07, Vlastimil Babka wrote: > On 9/9/21 10:56, 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. > > IIRC Fedora used to have CONFIG_DEBUG_VM enabled, did it change? Excellent question. Apparently you are right. Fortunately it's not a distro to use in production ;) In kernel-ark: redhat/configs/fedora/generic/CONFIG_DEBUG_VM:CONFIG_DEBUG_VM=y While for ARK (rhel-next so to say) redhat/configs/ark/generic/CONFIG_DEBUG_VM:# CONFIG_DEBUG_VM is not set So yes, the VM_WARN_ON would then be preferred in that case. But it's something that should never ever happen unless reviewers and developers really mess up, so I don't actually would sleep over that. We have other WARN... that can trigger more easily. > >> 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... > > Uh, does any distro really do that? Apparently, so I was told by Greg a year ago or so when wanting to add WARN_ON(). The advisory is to us pr_warn_once() instead. I rememebr it was a debian based distro. -- Thanks, David / dhildenb