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

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Message-ID: <alpine.DEB.2.00.1210311119000.8809@chino.kir.corp.google.com>
Date:	Wed, 31 Oct 2012 11:21:32 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Wen Congyang <wency@...fujitsu.com>
cc:	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()

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.
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