Re: [PATCH] mm: disallow direct reclaim page writeback

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> Hi
> 
> > How about this? For now, we stop direct reclaim from doing writeback
> > only on order zero allocations, but allow it for higher order
> > allocations. That will prevent the majority of situations where
> > direct reclaim blows the stack and interferes with background
> > writeout, but won't cause lumpy reclaim to change behaviour.
> > This reduces the scope of impact and hence testing and validation
> > the needs to be done.
> 
> Tend to agree. but I would proposed slightly different algorithm for
> avoind incorrect oom.
> 
> for high order allocation
> 	allow to use lumpy reclaim and pageout() for both kswapd and direct reclaim
> 
> for low order allocation
> 	- kswapd:          always delegate io to flusher thread
> 	- direct reclaim:  delegate io to flusher thread only if vm pressure is low
> 
> This seems more safely. I mean Who want see incorrect oom regression?
> I've made some pathes for this. I'll post it as another mail.

Now, kernel compile and/or backup operation seems keep nr_vmscan_write==0.
Dave, can you please try to run your pageout annoying workload?