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

From: Hillf Danton
Date: Mon Feb 20 2017 - 23:11:27 EST

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.