> > 1) File backed pages -> file > > > > dirty + writeback count remains constant > > > > 2) Anonymous pages -> swap > > > > writeback count increases, dirty balancing will hold back file > > writeback in favor of swap > > > > So the real question is: does case 2 need rate limiting, or is it OK > > to let the device queue fill with swap pages as fast as possible? > > > Because balance_dirty_pages() maintains: > > nr_dirty + nr_unstable + nr_writeback < > total_dirty + nr_cpus * ratelimit_pages > > throttle_vm_writeout() _should_ not deadlock on that, unless you're > caught in the error term: nr_cpus * ratelimit_pages.
And it does get caught on that in small memory machines. This deadlock is easily reproducable on a 32MB UML instance. I haven't yet tested with the per-bdi patches, but I don't think they make a difference in this case. > Which can only happen when it is larger than 10% of dirty_thresh. > > Which is even more unlikely since it doesn't account nr_dirty (as I > think it should). I think nr_dirty is totally irrelevant. Since we don't care about case 1), and in case 2) nr_dirty doesn't play any role. > As for 2), yes I think having a limit on the total number of pages in > flight is a good thing. Why? > But that said, there might be better ways to do that. Sure, if we do need to globally limit the number of under-writeback pages, then I think we need to do it independently of the dirty accounting. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
