Re: [PATCH] ovl: Allow changing default fsync_mode

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

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.

Not quite sure applying a default volatile policy is quite feasible,
especially the issue documented in
https://github.com/containerd/containerd/pull/10274/files#diff-9239161e2af83fd84df5792f9fe64701c517fe4598eae60d4d245d039955f46cR33

then userspace cannot drop `volatile` option as a somewhat
workaround now.

Thanks,
Gao Xiang

> 
> Add a Kconfig option to set the default fsync_mode at build time, and
> allow it to be overridden dynamically via a module parameter when
> loading overlayfs. This also aligns with how other features are
> configured.
> 
> Link: https://github.com/containerd/containerd/issues/6406 [0]
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>