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

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Message-ID: <20190924131939.GS23050@dhcp22.suse.cz>
Date:   Tue, 24 Sep 2019 15:19:39 +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 14:59:36, Peter Zijlstra wrote:
> On Tue, Sep 24, 2019 at 02:43:25PM +0200, Peter Zijlstra wrote:
> > On Tue, Sep 24, 2019 at 02:25:00PM +0200, Michal Hocko wrote:
> > > On Tue 24-09-19 14:09:43, Peter Zijlstra wrote:
> > 
> > > > We can push back and say we don't respect the specification because it
> > > > is batshit insane ;-)
> > > 
> > > Here is my fingers crossed.
> > > 
> > > [...]
> > > 
> > > > Now granted; there's a number of virtual devices that really don't have
> > > > a node affinity, but then, those are not hurt by forcing them onto a
> > > > random node, they really don't do anything. Like:
> > > 
> > > Do you really consider a random node a better fix than simply living
> > > with a more robust NUMA_NO_NODE which tells the actual state? Page
> > > allocator would effectivelly use the local node in that case. Any code
> > > using the cpumask will know that any of the online cpus are usable.
> > 
> > For the pmu devices? Yes, those 'devices' aren't actually used for
> > anything other than sysfs entries.
> > 
> > Nothing else uses the struct device.
> 
> The below would get rid of the PMU and workqueue warnings with no
> side-effects (the device isn't used for anything except sysfs).

Hardcoding to 0 is simply wrong, if the node0 is cpuless for example...
-- 
Michal Hocko
SUSE Labs