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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Sun, 11 Oct 2020 18:21:07 -0700
Message-ID: <CAADnVQJUL7BynGMD_nGu8y=D1yv6TybOxeSh03TrkD7kS0aOrA@mail.gmail.com>
Subject: Re: [PATCH] bpf: Avoid allocing memory on memoryless numa node
To:     Xianting Tian <tian.xianting@h3c.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        KP Singh <kpsingh@chromium.org>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Sat, Oct 10, 2020 at 1:55 AM Xianting Tian <tian.xianting@h3c.com> wrote:
>
> In architecture like powerpc, we can have cpus without any local memory
> attached to it. In such cases the node does not have real memory.
>
> Use local_memory_node(), which is guaranteed to have memory.
> local_memory_node is a noop in other architectures that does not support
> memoryless nodes.
...
>         /* Have map->numa_node, but choose node of redirect target CPU */
> -       numa = cpu_to_node(cpu);
> +       numa = local_memory_node(cpu_to_node(cpu));

There are so many calls to cpu_to_node() throughout the kernel.
Are you going to convert all of them one patch at a time to the above sequence?
Why not do this CONFIG_HAVE_MEMORYLESS_NODES
in cpu_to_node() instead?
and save the churn.