From: Michal Hocko <mhocko@kernel.org>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: dalias@libc.org, linux-sh@vger.kernel.org, peterz@infradead.org,
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Subject: Re: [PATCH v5] numa: make node_to_cpumask_map() NUMA_NO_NODE aware
Date: Tue, 17 Sep 2019 11:36:55 +0200 [thread overview]
Message-ID: <20190917093655.GA1872@dhcp22.suse.cz> (raw)
In-Reply-To: <d748aae4-4d48-6f8a-2f6d-67fad5224ba9@huawei.com>
On Tue 17-09-19 14:20:11, Yunsheng Lin wrote:
> On 2019/9/17 13:28, Michael Ellerman wrote:
> > Yunsheng Lin <linyunsheng@huawei.com> writes:
[...]
> >> But we cannot really copy the page allocator logic. Simply because the
> >> page allocator doesn't enforce the near node affinity. It just picks it
> >> up as a preferred node but then it is free to fallback to any other numa
> >> node. This is not the case here and node_to_cpumask_map will only restrict
> >> to the particular node's cpus which would have really non deterministic
> >> behavior depending on where the code is executed. So in fact we really
> >> want to return cpu_online_mask for NUMA_NO_NODE.
> >>
> >> Some arches were already NUMA_NO_NODE aware, but they return cpu_all_mask,
> >> which should be identical with cpu_online_mask when those arches do not
> >> support cpu hotplug, this patch also changes them to return cpu_online_mask
> >> in order to be consistent and use NUMA_NO_NODE instead of "-1".
> >
> > Except some of those arches *do* support CPU hotplug, powerpc and sparc
> > at least. So switching from cpu_all_mask to cpu_online_mask is a
> > meaningful change.
>
> Yes, thanks for pointing out.
>
> >
> > That doesn't mean it's wrong, but you need to explain why it's the right
> > change.
>
> How about adding the below to the commit log:
> Even if some of the arches do support CPU hotplug, it does not make sense
> to return the cpu that has been hotplugged.
>
> Any suggestion?
Again, for the third time, I believe. Make it a separate patch please.
There is absolutely no reason to conflate those two things.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-09-17 9:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-16 13:28 [PATCH v5] numa: make node_to_cpumask_map() NUMA_NO_NODE aware Yunsheng Lin
2019-09-17 5:28 ` Michael Ellerman
2019-09-17 6:20 ` Yunsheng Lin
2019-09-17 9:36 ` Michal Hocko [this message]
2019-09-17 9:53 ` Yunsheng Lin
2019-09-17 10:08 ` Michal Hocko
2019-09-17 11:36 ` Yunsheng Lin
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