On Tue 07-01-20 10:21:00, Dave Chinner wrote: > On Mon, Jan 06, 2020 at 12:55:14PM +0100, Michal Hocko wrote: > > On Tue 31-12-19 04:59:08, Matthew Wilcox wrote: > > > > > > I don't want to present this topic; I merely noticed the problem. > > > I nominate Jens Axboe and Michael Hocko as session leaders. See the > > > thread here: > > > > Thanks for bringing this up Matthew! The change in the behavior came as > > a surprise to me. I can lead the session for the MM side. > > > > > https://lore.kernel.org/linux-mm/20190923111900.GH15392@xxxxxxxxxxxxxxxxxxxxxx/ > > > > > > Summary: Congestion is broken and has been for years, and everybody's > > > system is sleeping waiting for congestion that will never clear. > > > > > > A good outcome for this meeting would be: > > > > > > - MM defines what information they want from the block stack. > > > > The history of the congestion waiting is kinda hairy but I will try to > > summarize expectations we used to have and we can discuss how much of > > that has been real and what followed up as a cargo cult. Maybe we just > > find out that we do not need functionality like that anymore. I believe > > Mel would be a great contributor to the discussion. > > We most definitely do need some form of reclaim throttling based on > IO congestion, because it is trivial to drive the system into swap > storms and OOM killer invocation when there are large dirty slab > caches that require IO to make reclaim progress and there's little > in the way of page cache to reclaim. Just to clarify. I do agree that we need some form of throttling. Sorry if my wording was confusing. What I meant is that I am not sure whether wait_iff_congested as it is implemented now is the right way. We definitely have to slow/block the reclaim when there is a lot of dirty (meta)data. How to do that is a good topic to discuss. [skipping the rest of the email which has many good points] -- Michal Hocko SUSE Labs
