Hello, On Tue, Jul 31, 2018 at 12:25:04AM +0900, Tetsuo Handa wrote: > WQ_MEM_RECLAIM guarantees that "struct task_struct" is preallocated. But > WQ_MEM_RECLAIM does not guarantee that the pending work is started as soon > as an item was queued. Same rule applies to both WQ_MEM_RECLAIM workqueues > and !WQ_MEM_RECLAIM workqueues regarding when to start a pending work (i.e. > when schedule_timeout_*() is called). > > Is this correct? WQ_MEM_RECLAIM guarantees that there's always gonna exist at least one kworker running the workqueue. But all per-cpu kworkers are subject to concurrency limiting execution - ie. if there are any per-cpu actively running on a cpu, no futher kworkers will be scheduled. > > We can add timeout mechanism to workqueue so that it > > kicks off other kworkers if one of them is in running state for too > > long, but idk, if there's an indefinite busy loop condition in kernel > > threads, we really should get rid of them and hung task watchdog is > > pretty effective at finding these cases (at least with preemption > > disabled). > > Currently the page allocator has a path which can loop forever with > only cond_resched(). Yeah, workqueue can choke on things like that and kthread indefinitely busy looping doesn't do anybody any good. Thanks. -- tejun
