On Fri, Jun 04, 2021 at 11:53:02AM -0400, Tejun Heo wrote:

On Thu, Jun 03, 2021 at 06:31:53PM -0700, Roman Gushchin wrote:

quoted

To solve the problem inodes should be eventually detached from the
corresponding writeback structure. It's inefficient to do it after
every writeback completion. Instead it can be done whenever the
original memory cgroup is offlined and writeback structure is getting
killed. Scanning over a (potentially long) list of inodes and detach
them from the writeback structure can take quite some time. To avoid
scanning all inodes, attached inodes are kept on a new list (b_attached).
To make it less noticeable to a user, the scanning and switching is performed
from a work context.

Sorry for chiming in late but the series looks great to me and the only
comment I have is the migration target on the last patch, which isn't a
critical issue. Please feel free to add

 Acked-by: Tejun Heo [off-list ref]

Thank you for taking a look and for acking the series!

I agree that switching to the nearest ancestor makes sense. If I remember
correctly, I was doing this in v1 (or at least planned to do), but then
switched to zeroing the pointer and then to bdi's wb.

I fixed it in v8 and pushed it here: https://github.com/rgushchin/linux/tree/cgwb.8 .
I'll wait a bit for Jan's and others feedback and will post v8 on Monday.
Hopefully, it will be the final version.

Btw, how are such patches usually routed? Through Jens's tree?

Thanks!