linux-kernel - Re: [PATCH v2 1/1] mm: only dispaly online cpus of the numa node

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Message-ID: <20171003134726.GC26552@arm.com>
Date:   Tue, 3 Oct 2017 14:47:26 +0100
From:   Will Deacon <will.deacon@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Zhen Lei <thunder.leizhen@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michal Hocko <mhocko@...e.com>, linux-mm <linux-mm@...ck.org>,
        Tianhong Ding <dingtianhong@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Libin <huawei.libin@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v2 1/1] mm: only dispaly online cpus of the numa node

On Mon, Oct 02, 2017 at 02:54:46PM -0700, Andrew Morton wrote:
> On Mon, 2 Oct 2017 11:38:07 +0100 Will Deacon <will.deacon@....com> wrote:
> 
> > > When I executed numactl -H(which read /sys/devices/system/node/nodeX/cpumap
> > > and display cpumask_of_node for each node), but I got different result on
> > > X86 and arm64. For each numa node, the former only displayed online CPUs,
> > > and the latter displayed all possible CPUs. Unfortunately, both Linux
> > > documentation and numactl manual have not described it clear.
> > > 
> > > I sent a mail to ask for help, and Michal Hocko <mhocko@...nel.org> replied
> > > that he preferred to print online cpus because it doesn't really make much
> > > sense to bind anything on offline nodes.
> > > 
> > > Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> > > Acked-by: Michal Hocko <mhocko@...e.com>
> > > ---
> > >  drivers/base/node.c | 12 ++++++++++--
> > >  1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > Which tree is this intended to go through? I'm happy to take it via arm64,
> > but I don't want to tread on anybody's toes in linux-next and it looks like
> > there are already queued changes to this file via Andrew's tree.
> 
> I grabbed it.  I suppose there's some small risk of userspace breakage
> so I suggest it be a 4.15-rc1 thing?

To be honest, I suspect the vast majority (if not all) code that reads this
file was developed for x86, so having the same behaviour for arm64 sounds
like something we should do ASAP before people try to special case with
things like #ifdef __aarch64__.

I'd rather have this in 4.14 if possible.

Cheers,

Will