Re: [PART6 Patch] mempolicy: fix is_valid_nodemask()

[Wen Congyang <wency@cn.fujitsu.com>]

At 11/01/2012 02:21 AM, David Rientjes Wrote:
> On Wed, 31 Oct 2012, Wen Congyang wrote:
> 
>> From: Lai Jiangshan <laijs@cn.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.
> 

Should we allow the user to bind a task to a node which has only ZONE_MOVABLE memory?

Thanks
Wen Congyang

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