On 11/8/19 1:18 PM, Tejun Heo wrote:
> cgroup writeback tries to refresh the associated wb immediately if the
> current wb is dead. This is to avoid keeping issuing IOs on the stale
> wb after memcg - blkcg association has changed (ie. when blkcg got
> disabled / enabled higher up in the hierarchy).
>
> Unfortunately, the logic gets triggered spuriously on inodes which are
> associated with dead cgroups. When the logic is triggered on dead
> cgroups, the attempt fails only after doing quite a bit of work
> allocating and initializing a new wb.
>
> While c3aab9a0bd91 ("mm/filemap.c: don't initiate writeback if mapping
> has no dirty pages") alleviated the issue significantly as it now only
> triggers when the inode has dirty pages. However, the condition can
> still be triggered before the inode is switched to a different cgroup
> and the logic simply doesn't make sense.
>
> Skip the immediate switching if the associated memcg is dying.
>
> This is a simplified version of the following two patches:
>
> * https://lore.kernel.org/linux-mm/20190513183053.GA73423@dennisz-mbp/
> * http://lkml.kernel.org/r/156355839560.2063.5265687291430814589.stgit@buzz
Applied for 5.4, thanks.
--
Jens Axboe
