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

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]

Thanks.

-- 
tejun