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([2a03:a900:1000:7e9:403e:7c8b:351b:f333]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a6c8070e82esm148278266b.161.2024.06.06.15.18.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Jun 2024 15:18:00 -0700 (PDT) Message-ID: Date: Fri, 7 Jun 2024 00:17:59 +0200 Precedence: bulk X-Mailing-List: linux-lvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: lvm2 deadlock From: Zdenek Kabelac To: Jaco Kroon , Roger Heflin Cc: "linux-lvm@lists.linux.dev" References: <9bac4556-bdf8-4034-9322-522277ff311e@uls.co.za> <66d9e7cf-b654-4476-b1e2-e3bdf4444280@uls.co.za> <5aa7f229-aef5-4f63-acb5-1e130c6c5296@uls.co.za> <77882d4d-91e4-4625-ab98-97738d13da8b@uls.co.za> <67629722-b281-4ee9-b832-08e85c09efd5@gmail.com> Content-Language: en-US, cs In-Reply-To: <67629722-b281-4ee9-b832-08e85c09efd5@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Dne 07. 06. 24 v 0:14 Zdenek Kabelac napsal(a): > Dne 05. 06. 24 v 10:59 Jaco Kroon napsal(a): >> Hi, >> >> On 2024/06/04 18:07, Zdenek Kabelac wrote: >>> Dne 04. 06. 24 v 13:52 Jaco Kroon napsal(a): >>> Last but not least -  disk scheduling policies also do have impact - to >>> i.e. ensure better fairness - at the prices of lower throughput... >> We normally use mq-deadline, in this setup I notice this has been updated to >> "none", the plan was to revert, this was done in collaboration with a >> discussion with Bart van Assche.  Happy to revert this to be honest. >> https://lore.kernel.org/all/07d8b189-9379-560b-3291-3feb66d98e5c@acm.org/ >> relates. > > Hi > > So I guess we can tell the store like this - > > When you've created your 'snapshot' of a thin-volume - this enforces full > flush (& fsfreeze) of a thin volume - so any dirty pages need to written in > thin pool before snapshot could be taken (and thin pool should not run out of > space) - this CAN potentially hold your system running for a long time > (depending on performance of your storage) and may cause various lock-ups > states of your system if you are using this 'snapshoted' volume for anything > else - as the volume is suspended - so it blocks further operations on this > device  - eventually causing full system circular deadlock  (catch 22) - this > is hard to analyze without whole picture of the system. > > We may eventually think whether we can somehow minimize the amount of holding > vglock and suspending with flush & fsfreeze -  but it's about some future > possible enhancement and flush disk upfront to minimize dirty size. I've forget to mention that a 'simplest' way is just to run 'sync' before running 'lvcreate -s...' command... Regards Zdenek