Hi
> > > > > out:
> > > > > - if (!all_zones_ok) {
> > > > > + if (!(all_zones_ok || (order && any_zone_ok))) {
> > > >
> > > > This doesn't work ;)
> > > > kswapd have to clear ZONE_CONGESTED flag before enter sleeping.
> > > > otherwise nobody can clear it.
> > > >
> > >
> > > Does it not do it earlier in balance_pgdat() here
> > >
> > > /*
> > > * If a zone reaches its high watermark,
> > > * consider it to be no longer congested. It's
> > > * possible there are dirty pages backed by
> > > * congested BDIs but as pressure is
> > > * relieved, spectulatively avoid congestion waits
> > > */
> > > zone_clear_flag(zone, ZONE_CONGESTED);
> > > if (i <= pgdat->high_zoneidx)
> > > any_zone_ok = 1;
> >
> > zone_clear_flag(zone, ZONE_CONGESTED) only clear one zone status. other
> > zone remain old status.
> >
>
> Ah now I get you. kswapd does not necessarily balance all zones so it needs
> to unconditionally clear them all before it goes to sleep in case. At
> some time in the future, the tagging of ZONE_CONGESTED needs more
> thinking about.
>
This is a option.
> > > > Say, we have to fill below condition.
> > > > - All zone are successing zone_watermark_ok(order-0)
> > >
> > > We should loop around at least once with order == 0 where all_zones_ok
> > > is checked.
> >
> > But no gurantee. IOW kswapd early stopping increase GFP_ATOMIC allocation
> > failure risk, I think.
> >
>
> Force all zones to be balanced for order-0?
Yes.
I think following change does.
if (i <= pgdat->high_zoneidx)
- any_zone_ok = 1;
+ order = sc.order = 0;
This is more conservative.
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