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Subject: Re: [PATCH RFC v2 4/4] mm/mempolicy: add nodes_empty check in
 SYSC_migrate_pages
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From: Vlastimil Babka <vbabka@suse.cz>
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Date: Tue, 7 Nov 2017 16:05:10 +0100
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To: Christopher Lameter <cl@linux.com>, Yisheng Xie <xieyisheng1@huawei.com>
Cc: akpm@linux-foundation.org, mhocko@suse.com, mingo@kernel.org, rientjes@google.com, n-horiguchi@ah.jp.nec.com, salls@cs.ucsb.edu, linux-mm@kvack.org, linux-kernel@vger.kernel.org, tanxiaojun@huawei.com, linux-api@vger.kernel.org, Andi Kleen <ak@linux.intel.com>

On 11/07/2017 03:54 PM, Christopher Lameter wrote:
> On Tue, 7 Nov 2017, Yisheng Xie wrote:
> 
>> On 2017/11/6 23:29, Christopher Lameter wrote:
>>> On Mon, 6 Nov 2017, Vlastimil Babka wrote:
>>>
>>>> I'm not sure what exactly is the EPERM intention. Should really the
>>>> capability of THIS process override the cpuset restriction of the TARGET
>>>> process? Maybe yes. Then, does "insufficient privilege (CAP_SYS_NICE) to
>>>
>>> CAP_SYS_NICE never overrides cpuset restrictions. The cap can be used to
>>> migrate pages that are *also* mapped by other processes (and thus move
>>> pages of another process which may have different cpu set restrictions!).
>>
>> So you means the specified nodes should be a subset of target cpu set, right?
> 
> The specified nodes need to be part of the *current* cpu set.
> 
> Migrate pages moves the pages of a single process there is no TARGET
> process.

migrate_pages(2) takes a pid argument

"migrate_pages()  attempts  to  move all pages of the process pid that
are in memory nodes old_nodes to the memory nodes in new_nodes. "

> Thus thehe *target* nodes need to be a subset of the current cpu set.
> 
> 
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