On Thu, 2019-10-10 at 19:30 +0200, Michal Hocko wrote: > On Thu 10-10-19 10:47:38, Qian Cai wrote: > > On Thu, 2019-10-10 at 16:18 +0200, Michal Hocko wrote: > > > On Thu 10-10-19 09:11:52, Qian Cai wrote: > > > > On Thu, 2019-10-10 at 12:59 +0200, Michal Hocko wrote: > > > > > On Thu 10-10-19 05:01:44, Qian Cai wrote: > > > > > > > > > > > > > > > > > > > On Oct 9, 2019, at 12:23 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > If this was only about the memory offline code then I would agree. But > > > > > > > we are talking about any printk from the zone->lock context and that is > > > > > > > a bigger deal. Besides that it is quite natural that the printk code > > > > > > > should be more universal and allow to be also called from the MM > > > > > > > contexts as much as possible. If there is any really strong reason this > > > > > > > is not possible then it should be documented at least. > > > > > > > > > > > > Where is the best place to document this? I am thinking about under > > > > > > the “struct zone” definition’s lock field in mmzone.h. > > > > > > > > > > I am not sure TBH and I do not think we have reached the state where > > > > > this would be the only way forward. > > > > > > > > How about I revised the changelog to focus on memory offline rather than making > > > > a rule that nobody should call printk() with zone->lock held? > > > > > > If you are to remove the CONFIG_DEBUG_VM printk then I am all for it. I > > > am still not convinced that fiddling with dump_page in the isolation > > > code is justified though. > > > > No, dump_page() there has to be fixed together for memory offline to be useful. > > What's the other options it has here? > > I would really prefer to not repeat myself > http://lkml.kernel.org/r/20191010074049.GD18412@xxxxxxxxxxxxxx Care to elaborate what does that mean? I am confused on if you finally agree on no printk() while held zone->lock or not. You said "If there is absolutely no way around that then we might have to bite a bullet and consider some of MM locks a land of no printk." which makes me think you agreed, but your stance from the last reply seems you were opposite to it. > > > By not holding zone->lock in dump_page() > > from set_migratetype_isolate(), it even has a good side-effect to increase the > > system throughput as dump_page() could be time-consuming. It may make the code a > > bit cleaner by introducing a has_unmovable_pages_locked() version. > > I do not see why we should really optimize this cold path.
