Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx

[Hillf Danton]

On February 21, 2017 12:34 AM Vlastimil Babka wrote:
> On 02/16/2017 09:21 AM, Hillf Danton wrote:
> > Right, but the order-3 request can also come up while kswapd is active and
> > gives up order-5.
> 
> "Giving up on order-5" means it will set sc.order to 0, go to sleep (assuming
> order-0 watermarks are OK) and wakeup kcompactd for order-5. There's no way how
> kswapd could help an order-3 allocation at that point - it's up to kcompactd.
> 
	cpu0				cpu1
	give up order-5 
	fall back to order-0
					wake up kswapd for order-3 
					wake up kswapd for order-5
	fall in sleep
					wake up kswapd for order-3
	what order would
	we try?

It is order-5 in the patch. 

Given the fresh new world without hike ban after napping, 
one tenth second or 3 minutes, we feel free IMHO to select
any order and go another round of reclaiming pages.

thanks
Hillf