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 08:54:46 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Yisheng Xie <xieyisheng1@...wei.com>
cc:     Vlastimil Babka <vbabka@...e.cz>, 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 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.

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