linux-kernel - Re: [PATCH RFC v2 4/4] mm/mempolicy: add nodes_empty check in SYSC_migrate

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

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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