Re: [PATCH] ovl: Allow changing default fsync_mode

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2026/6/23 17:59, Yafang Shao wrote:
> On Tue, Jun 23, 2026 at 5:49 PM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>
>>
>>
>> On 2026/6/23 17:34, Yafang Shao wrote:
>>> On Tue, Jun 23, 2026 at 5:25 PM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>>>
>>>>
>>>>
>>>> On 2026/6/23 17:15, Yafang Shao wrote:
>>>>> On Tue, Jun 23, 2026 at 5:00 PM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 2026/6/23 16:43, Yafang Shao wrote:
>>>>>>> We have enabled "volatile" fsync_mode on our Kubernetes production
>>>>>>> environment to prevent container exit from being blocked when there
>>>>>>> are many dirty pages to flush. This has worked well without introducing
>>>>>>> any issues.
>>>>>>>
>>>>>>> However, on some of our production servers, upgrading the container
>>>>>>> runtime to support the "volatile" mount option is not straightforward [0].
>>>>>>> To address this, we want to enable it by default within the kernel.
>>>>>>
>>>>>> Just a side note: "upgrade the container runtime is not
>>>>>> straightforward", how? it seems that issue is already resolved and
>>>>>> there is no more discussion.
>>>>>
>>>>> We still have many production servers running Docker, while the
>>>>> "volatile" mount option is only supported by containerd. Upgrading
>>>>> from Docker to containerd is a difficult process.
>>>>
>>>> But docker can be patched too: if upgrading the userspace is
>>>> hard, why upgrading the linux kernel is easy?
>>>
>>> It is quite easy since the kernel can be livepatched without
>>> rebooting. My employer is a heavy livepatch user. [1]
>>>
>>> [1]. https://lore.kernel.org/live-patching/
>>
>> It's just a generic opinion, in general, docker can be live
>> upgraded without pausing the containers, and upgrading
>> userspace is easier / safer than patching the kernel.
> 
> Are you sure? How would one change an already mounted overlayfs that
> was not enabled with "volatile"?
> 
I don't see how your patch can apply to already mounted
overlayfs.

Again, I don't want such customized messy breaks userspace
again; with that patch, container runtime needs to consider
if `volatile` is the default which just breaks the existing
containerd versions.

Thanks,
Gao Xiang