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Date:   Tue, 16 Apr 2019 16:39:58 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Yang Shi <yang.shi@linux.alibaba.com>, mgorman@techsingularity.net,
        riel@surriel.com, hannes@cmpxchg.org, akpm@linux-foundation.org,
        keith.busch@intel.com, dan.j.williams@intel.com,
        fengguang.wu@intel.com, fan.du@intel.com, ying.huang@intel.com,
        ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node
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On Tue 16-04-19 07:30:20, Dave Hansen wrote:
> On 4/16/19 12:47 AM, Michal Hocko wrote:
> > You definitely have to follow policy. You cannot demote to a node which
> > is outside of the cpuset/mempolicy because you are breaking contract
> > expected by the userspace. That implies doing a rmap walk.
> 
> What *is* the contract with userspace, anyway? :)
> 
> Obviously, the preferred policy doesn't have any strict contract.
> 
> The strict binding has a bit more of a contract, but it doesn't prevent
> swapping.

Yes, but swapping is not a problem for using binding for memory
partitioning.

> Strict binding also doesn't keep another app from moving the
> memory.

I would consider that a bug.
-- 
Michal Hocko
SUSE Labs