linux-kernel - Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone

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Date:   Tue, 21 Feb 2017 12:10:34 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Vlastimil Babka'" <vbabka@...e.cz>,
        "'Mel Gorman'" <mgorman@...hsingularity.net>
Cc:     "'Andrew Morton'" <akpm@...ux-foundation.org>,
        "'Shantanu Goel'" <sgoel01@...oo.com>,
        "'Chris Mason'" <clm@...com>,
        "'Johannes Weiner'" <hannes@...xchg.org>,
        "'LKML'" <linux-kernel@...r.kernel.org>,
        "'Linux-MM'" <linux-mm@...ck.org>
Subject: Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx

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