Re: [PATCH v4 1/1] os-posix: asynchronous teardown for shutdown on Linux

[Daniel P . Berrangé]

On Fri, Aug 12, 2022 at 03:34:53PM +0200, 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/<QEMU_PID>". 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:
> 
>   <commandline xmlns="http://libvirt.org/schemas/domain/qemu/1.0";>
>   <arg value='-async-teardown'/>
>   </commandline>
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Reviewed-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> Tested-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> ---
>  include/qemu/async-teardown.h |  22 +++++
>  meson.build                   |   1 +
>  os-posix.c                    |   6 ++
>  qemu-options.hx               |  19 +++++
>  util/async-teardown.c         | 155 ++++++++++++++++++++++++++++++++++
>  util/meson.build              |   1 +
>  6 files changed, 204 insertions(+)
>  create mode 100644 include/qemu/async-teardown.h
>  create mode 100644 util/async-teardown.c

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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