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[149.6.153.187]) by smtp.googlemail.com with ESMTPSA id bi24-20020a05620a319800b006eeca296c00sm2014713qkb.104.2022.10.25.05.42.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Oct 2022 05:42:13 -0700 (PDT) Message-ID: Date: Tue, 25 Oct 2022 14:42:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [PATCH v4 1/1] os-posix: asynchronous teardown for shutdown on Linux Content-Language: en-US To: Claudio Imbrenda Cc: qemu-devel@nongnu.org, david@redhat.com, cohuck@redhat.com, thuth@redhat.com, borntraeger@de.ibm.com, frankja@linux.ibm.com, fiuczy@linux.ibm.com, pasic@linux.ibm.com, berrange@redhat.com, alex.bennee@linaro.org, armbru@redhat.com, Murilo Opsfelder Araujo References: <20220812133453.82671-1-imbrenda@linux.ibm.com> From: Paolo Bonzini In-Reply-To: <20220812133453.82671-1-imbrenda@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.517, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Qemu-devel" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 8/12/22 15:34, Claudio Imbrenda wrote: > This patch adds support for asynchronously tearing down a VM on Linux. > > When qemu terminates, either naturally or because of a fatal signal, > the VM is torn down. If the VM is huge, it can take a considerable > amount of time for it to be cleaned up. In case of a protected VM, it > might take even longer than a non-protected VM (this is the case on > s390x, for example). > > Some users might want to shut down a VM and restart it immediately, > without having to wait. This is especially true if management > infrastructure like libvirt is used. > > This patch implements a simple trick on Linux to allow qemu to return > immediately, with the teardown of the VM being performed > asynchronously. > > If the new commandline option -async-teardown is used, a new process is > spawned from qemu at startup, using the clone syscall, in such way that > it will share its address space with qemu.The new process will have the > name "cleanup/". It will wait until qemu terminates > completely, and then it will exit itself. > > This allows qemu to terminate quickly, without having to wait for the > whole address space to be torn down. The cleanup process will exit > after qemu, so it will be the last user of the address space, and > therefore it will take care of the actual teardown. The cleanup > process will share the same cgroups as qemu, so both memory usage and > cpu time will be accounted properly. > > If possible, close_range will be used in the cleanup process to close > all open file descriptors. If it is not available or if it fails, /proc > will be used to determine which file descriptors to close. > > If the cleanup process is forcefully killed with SIGKILL before the > main qemu process has terminated completely, the mechanism is defeated > and the teardown will not be asynchronous. > > This feature can already be used with libvirt by adding the following > to the XML domain definition to pass the parameter to qemu directly: > > > > > > Signed-off-by: Claudio Imbrenda > Reviewed-by: Murilo Opsfelder Araujo > Tested-by: Murilo Opsfelder Araujo > --- Nice trick indeed! The only question I have is whether it would make sense to do this in Libvirt instead. Having a new independent one-off option like this is not great, but I think it's fine because it's not a very reusable grouping. Paolo