On Fri, Aug 02, 2019 at 09:58:49AM +1000, Dave Chinner wrote: > Which simply reinforces the fact that that request type based > throttling is a fundamentally broken architecture. > > > It feels awkward to have one set of prio inversion workarounds for io.* > > and another for wbt. Jens, should we make an explicit one that doesn't > > rely on magic side effects, or just decide that metadata is meta enough > > to break all the rules? > > The problem isn't REQ_META blows throw the throttling, the problem > is that different REQ_META IOs have different priority. > > IOWs, the problem here is that we are trying to infer priority from > the request type rather than an actual priority assigned by the > submitter. There is no way direct IO has higher priority in a > filesystem than log IO tagged with REQ_META as direct IO can require > log IO to make progress. Priority is a policy determined by the > submitter, not the mechanism doing the throttling. > > Can we please move this all over to priorites based on > bio->b_ioprio? And then document how the range of priorities are > managed, such as: Yes, we need to fix the magic deducted throttling behavior, especiall the odd REQ_IDLE that in its various incarnations has been a massive source of toruble and confusion. Not sure tons of priorities are really helping, given that even hardware with priority level support usually just supports about two priorit levels.
