linux-kernel - Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO

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Message-ID: <20190924115401.GM23050@dhcp22.suse.cz>
Date:   Tue, 24 Sep 2019 13:54:01 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>, catalin.marinas@....com,
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Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware

On Tue 24-09-19 13:23:49, Peter Zijlstra wrote:
> On Tue, Sep 24, 2019 at 12:56:22PM +0200, Michal Hocko wrote:
[...]
> > To be honest I really fail to see why to object to a simple semantic
> > that NUMA_NO_NODE imply all usable cpus. Could you explain that please?
> 
> Because it feels wrong. The device needs to be _somewhere_. It simply
> cannot be node-less.

What if it doesn't have any numa preference for what ever reason? There
is no other way to express that than NUMA_NO_NODE.

Anyway, I am not going to argue more about this because it seems more of
a discussion about "HW shouldn't be doing that although the specification
allows that" which cannot really have any outcome except of "feels
correct/wrong".

If you really feel strongly about this then we should think of a proper
way to prevent this to happen because an out-of-bound access is
certainly not something we really want, right?
-- 
Michal Hocko
SUSE Labs