linux-kernel - Re: [PART6 Patch] mempolicy: fix is_valid

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Message-ID: <50936288.5090008@jp.fujitsu.com>
Date:	Fri, 02 Nov 2012 15:04:56 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Wen Congyang <wency@...fujitsu.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-doc@...r.kernel.org,
	Rob Landley <rob@...dley.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mgorman@...e.de>, Yinghai Lu <yinghai@...nel.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>
Subject: Re: [PART6 Patch] mempolicy: fix is_valid_nodemask()

(2012/11/01 3:21), David Rientjes wrote:
> On Wed, 31 Oct 2012, Wen Congyang wrote:
>
>> From: Lai Jiangshan <laijs@...fujitsu.com>
>>
>> is_valid_nodemask() is introduced by 19770b32. but it does not match
>> its comments, because it does not check the zone which > policy_zone.
>>
>> Also in b377fd, this commits told us, if highest zone is ZONE_MOVABLE,
>> we should also apply memory policies to it. so ZONE_MOVABLE should be valid zone
>> for policies. is_valid_nodemask() need to be changed to match it.
>>
>> Fix: check all zones, even its zoneid > policy_zone.
>> Use nodes_intersects() instead open code to check it.
>>
>
> This changes the semantics of MPOL_BIND to be considerably different than
> what it is today: slab allocations are no longer bound by such a policy
> which isn't consistent with what userspace expects or is specified by
> set_mempolicy() and there's no way, with your patch, to actually specify
> that we don't care about ZONE_MOVABLE and that the slab allocations
> _should_ actually be allocated on movable-only zones.  You have to respect
> cases where people aren't interested in node hotplug and not cause a
> regression.
>

I'm sorry if I misunderstand somehing....
I think people doesn't insterested in node-hotplug will never have MOVABLE_ZONE.
What causes regression ?

Thanks,
-Kame




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