linux-kernel - RE: [PATCH] bpf: Avoid allocing memory on memoryless numa node

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Message-ID: <21cff6313475470e9b316911c748f890@h3c.com>
Date:   Mon, 12 Oct 2020 01:26:01 +0000
From:   Tianxianting <tian.xianting@....com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "John Fastabend" <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        "Song Liu" <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] bpf: Avoid allocing memory on memoryless numa node

Thanks Alexei for your suggestion,
I will try to do it.

-----Original Message-----
From: Alexei Starovoitov [mailto:alexei.starovoitov@...il.com] 
Sent: Monday, October 12, 2020 9:21 AM
To: tianxianting (RD) <tian.xianting@....com>
Cc: Alexei Starovoitov <ast@...nel.org>; Daniel Borkmann <daniel@...earbox.net>; David S. Miller <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>; Jesper Dangaard Brouer <hawk@...nel.org>; John Fastabend <john.fastabend@...il.com>; Martin KaFai Lau <kafai@...com>; Song Liu <songliubraving@...com>; Yonghong Song <yhs@...com>; Andrii Nakryiko <andriin@...com>; KP Singh <kpsingh@...omium.org>; Network Development <netdev@...r.kernel.org>; bpf <bpf@...r.kernel.org>; LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: Avoid allocing memory on memoryless numa node

On Sat, Oct 10, 2020 at 1:55 AM Xianting Tian <tian.xianting@....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.