On Sat 13-08-16 13:34:29, Mikulas Patocka wrote: > > > On Fri, 12 Aug 2016, Michal Hocko wrote: > > > On Thu 04-08-16 14:49:41, Mikulas Patocka wrote: > > > > > On Wed, 3 Aug 2016, Michal Hocko wrote: > > > > > > > But the device congestion is not the only condition required for the > > > > throttling. The pgdat has also be marked congested which means that the > > > > LRU page scanner bumped into dirty/writeback/pg_reclaim pages at the > > > > tail of the LRU. That should only happen if we are rotating LRUs too > > > > quickly. AFAIU the reclaim shouldn't allow free ticket scanning in that > > > > situation. > > > > > > The obvious problem here is that mempool allocations should sleep in > > > mempool_alloc() on &pool->wait (until someone returns some entries into > > > the mempool), they should not sleep inside the page allocator. > > > > I agree that mempool_alloc should _primarily_ sleep on their own > > throttling mechanism. I am not questioning that. I am just saying that > > the page allocator has its own throttling which it relies on and that > > cannot be just ignored because that might have other undesirable side > > effects. So if the right approach is really to never throttle certain > > requests then we have to bail out from a congested nodes/zones as soon > > as the congestion is detected. > > > > Now, I would like to see that something like that is _really_ necessary. > > Currently, it is not a problem - device mapper reports the device as > congested only if the underlying physical disks are congested. > > But once we change it so that device mapper reports congested state on its > own (when it has too many bios in progress), this starts being a problem. OK, can we wait until it starts becoming a real problem and solve it appropriately then? I will repost the patch which removes thottle_vm_pageout in the meantime as it doesn't seem to be needed anymore. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>