On Wed, Mar 29, 2023 at 09:16:18AM -1000, Tejun Heo wrote: > We didn't really look deep into adding the support but Chris mentioned that > raid5/6 are likely to need something similar. Maybe this is because my grasp > of filesytsems is pretty weak but the pattern doesn't seem unreasonable to > me. There's some work to be done by a shread kthread and that sometimes can > fork out IOs which belong to specific cgroups. Well, in a cgroup aware writeback path we'd always be off much better to just do the work from a cgroup specific thread instead of bouncing it around. > At least in the IO control and direct issue path, punting to just one thread > hasn't been a practical problem given that when the issuing thread needs to > be blocked, either the whole device or the cgroup needs to be throttled > anyway. I don't think it is a problem per see. But it is: a) inefficient and b) complex in terms of code. So why bounce around between 2, or in case of writeback 3 threads for a single I/O, instead of making sure your offload threads are simplify cgroup specific to start with?
