linux-kernel - RE: [PATCH] kswapd: assign new_order and new_classzone

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Date:	Fri, 29 Jul 2011 23:33:26 +0800
From:	"Shi, Alex" <alex.shi@...el.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"P@...igBrady.com" <P@...igBrady.com>,
	"mgorman@...e.de" <mgorman@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"andrea@...share.com" <andrea@...share.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"riel@...hat.com" <riel@...hat.com>, "luto@....edu" <luto@....edu>
Subject: RE: [PATCH] kswapd: assign new_order and new_classzone_idx after
 wakeup in sleeping

> -----Original Message-----
> From: Minchan Kim [mailto:minchan.kim@...il.com]
> Sent: Friday, July 29, 2011 4:57 PM
> To: Shi, Alex
> Cc: majordomo@...ck.org; P@...igBrady.com; mgorman@...e.de;
> linux-kernel@...r.kernel.org; andrea@...share.com; Chen, Tim C; Li,
> Shaohua; akpm@...ux-foundation.org; riel@...hat.com; luto@....edu
> Subject: Re: [PATCH] kswapd: assign new_order and new_classzone_idx after
> wakeup in sleeping
> 
> On Fri, Jul 29, 2011 at 09:34:42AM +0800, Alex Shi wrote:
> > There 2 place to read pgdat in kswapd. One is return from a successful
> > balance, another is waked up from sleeping. But the new_order and
> > new_classzone_idx are not assigned after kswapd_try_to_sleep(), that
> > will cause a bug in the following scenario.
> >
> > After the last time successful balance, kswapd goes to sleep. So the
> > new_order and new_classzone_idx were assigned to 0 and MAX-1 since there
> > is no new wakeup during last time balancing. Now, a new wakeup came and
> > finish balancing successful with order > 0. But since new_order is still
> > 0, this time successful balancing were judged as a failed balance. so,
> > if there is another new wakeup coming during balancing, kswapd cann't
> > read this and still want to try to sleep. And if the new wakeup is a
> > tighter request, kswapd may goes to sleep, not to do balancing. That is
> > incorrect.
> >
> > So, to avoid above problem, the new_order and new_classzone_idx need to
> > be assigned for later successful comparison.
> >
> > Paidrag Brady, Could like do a retry for your problem on this patch?
> >
> > Signed-off-by: Alex Shi <alex.shi@...el.com>
> > Acked-by: Mel Gorman <mgorman@...e.de>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>

Thanks for review. 
BTW, I remove the incorrect email address of linux-mm. sorry for this! 
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