On Mon, Jun 23, 2014 at 11:25:21PM -0400, Tejun Heo wrote: > Hello, > > On Tue, Jun 24, 2014 at 01:02:40PM +1000, Dave Chinner wrote: > > As I understand it, what then happens is that the workqueue code > > grabs another kworker thread and runs the next work item in it's > > queue. IOWs, work items can block, but doing that does not prevent > > execution of other work items queued on other work queues or even on > > the same work queue. Tejun, did I get that correct? > > Yes, as long as the workqueue is under its @max_active limit and has > access to an existing kworker or can create a new one, it'll start > executing the next work item immediately; however, the guaranteed > level of concurrency is 1 even for WQ_RECLAIM workqueues. IOW, the > work items queued on a workqueue must be able to make forward progress > with single work item if the work items are being depended upon for > memory reclaim. Hmmm - that's different from my understanding of what the original behaviour WQ_MEM_RECLAIM gave us. i.e. that WQ_MEM_RECLAIM workqueues had a rescuer thread created to guarantee that the *workqueue* could make forward progress executing work in a reclaim context. The concept that the *work being executed* needs to guarantee forwards progress is something I've never heard stated before. That worries me a lot, especially with all the memory reclaim problems that have surfaced in the past couple of months.... > As long as a WQ_RECLAIM workqueue dosen't depend upon itself, > forward-progress is guaranteed. I can't find any documentation that actually defines what WQ_MEM_RECLAIM means, so I can't tell when or how this requirement came about. If it's true, then I suspect most of the WQ_MEM_RECLAIM workqueues in filesystems violate it. Can you point me at documentation/commits/code describing the constraints of WQ_MEM_RECLAIM and the reasons for it? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
