On Fri, 30 Oct 2015, Alan Stern wrote: > > > > I would say instead "no I/O is allowed from now on". Maybe that's an > > > > overstatement, but I think it comes closer to the truth. > > > > But that's what PM callbacks are for. > > Why are PM callbacks any more suitable than the freezer? Once the PM callback triggers, you know that you are really actually undergoing suspend and have to do whatever is necessary. OTOH, try_to_freeze() is a kind of "are we there yet?" polling, and the whole state needs to be prepared pro-actively for suspend already when you call it, each and every time, even if you are not going through suspend at all. That's sub-optimal, and very easy to get wrong over gradual code changes. > The most natural implementation would be for the callback routine to set > a flag; at various strategic points the kthread would check the flag and > if it was set, call a routine that sits around and waits for the suspend > to be over. Could you name at least some existing kthreads that would actually *need* such complex handling, instead of just waiting in schedule() until suspend-resume cycle is over, given that PM callbacks do all the necessary cleanup (putting HW to sleep, cancelling timers, etc) anyway? PM callback can always explicitly do kthread_stop() on a particular kthread if really necessary. > Also, you never replied to my question about suspend vs. hibernation. The main point of freezer is to reach quiescent state wrt. filesystems (metadata in memory need to be absolutely in sync with what's on disk). That's no different between hibernation and s2ram, is it? BTW, a quite some of this has been already "pre-discussed" in Documentation/power/freezing-of-tasks.txt (which has BTW been written before we've had the possibility to freeze filesystems, and this fact is even point there out). Thanks, -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
