From: Zheng Chuan <zhengchuan@huawei.com>
To: "Steven Sistare" <steven.sistare@oracle.com>,
"Qemu Developers" <qemu-devel@nongnu.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Juan Quintela" <quintela@redhat.com>,
"Daniel P. Berrangé" <berrange@redhat.com>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
Xiexiangyou <xiexiangyou@huawei.com>
Subject: Re: [PATCH V5 00/25] Live Update [restart] : fork mode?
Date: Thu, 5 Aug 2021 22:04:25 +0800 [thread overview]
Message-ID: <998c8c53-a4ee-b25f-62f9-47179d4a81bc@huawei.com> (raw)
In-Reply-To: <d9539fbb-1f98-fa2e-f465-3cfbfdd50e0e@oracle.com>
Hi, Steve.
On 2021/8/5 4:50, Steven Sistare wrote:
> On 7/30/2021 9:10 AM, Zheng Chuan wrote:
>> Hi, Steve
>> I have saw the discussion about the fork+exec mode below:
>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg815956.html
>>
>> And I am still very curious and I want to discuss about the possibility to support both fork+exec and exec in cpr framework.
>>
>> 1.Why
>> fork+exec could have some advantages and also drawbacks versus execvp() directly.
>> Advantages
>> i) fork+exec give the chance to fallback to original process even after we do exec which is important for workload seamless if any error happens.
>> ii) smaller downtime since we could remove the vm_start() downtime out of the frozen window.
>> Drawbacks
>> i)need more codes to handle including fork,address/ports conflict between parent and child.
>> ii)more complex life cycle management for the two processes.
>>
>> 2.How
>> The cpr framework is flexible and scalable, and maybe we can make use of most codes to support both execvp and fork+exec mode.
>> However, we may need to do more work compared to execvp method.
>> i) do fork mode in a thread like migration thread
>> ii) make parent and child talk to each other through socket or anonymous pipe
>> iii)make use of sharing mechanism of fds in cpr framework including memfd, vfio and devices fds
>> iv)deal with the conflict about the socket address and port like vnc (do by reuse port and pass the different args by cprexec)
>> v) do life cycle managements for two qemu processes and need parent exit and reconnection for the child at last by the management service
>>
>> Please tell me if I am missing something important:)
>
> Hi Zheng, that list sounds about right. However, additional kernel changes would be needed to
> change ownership of the vfio device descriptors. The vfio module records the mm of the creating
> process, and does not allow other processes to unmap ranges. Also, the mm->locked_vm would
> need to be transferred to the new process.
>
Oh,That's right. Maybe we could update them along with VFIO_DMA_MAP_FLAG_VADDR.
> Fork+exec could be a new mode to the cprsave command.
>
Yeah, I would be very happy to see it in the future:)
> - Steve
> .
>
--
Regards.
Chuan
prev parent reply other threads:[~2021-08-05 14:10 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-30 13:10 [PATCH V5 00/25] Live Update [restart] : fork mode? Zheng Chuan
2021-08-04 9:30 ` Zheng Chuan
2021-08-04 20:50 ` Steven Sistare
2021-08-05 14:04 ` Zheng Chuan [this message]
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