linux-kernel - Re: [RFC PATCH] fs/exec: Add the support for ELF program's NUMA replication

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Message-ID: <1c115101-a549-0e88-7bbb-1b0a19621504@redhat.com>
Date:   Thu, 9 Sep 2021 10:58:49 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Huang Shijie <shijie@...amperecomputing.com>
Cc:     viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        jlayton@...nel.org, bfields@...ldses.org,
        torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        song.bao.hua@...ilicon.com, patches@...erecomputing.com,
        zwang@...erecomputing.com
Subject: Re: [RFC PATCH] fs/exec: Add the support for ELF program's NUMA
 replication

On 09.09.21 11:46, Huang Shijie wrote:
> On Mon, Sep 06, 2021 at 11:35:01AM +0200, David Hildenbrand wrote:
>> On 06.09.21 18:16, Huang Shijie wrote:
>>> This patch adds AT_NUMA_REPLICATION for execveat().
>>>
>>> If this flag is set, the kernel will trigger COW(copy on write)
>>> on the mmapped ELF binary. So the program will have a copied-page
>>> on its NUMA node, even if the original page in page cache is
>>> on other NUMA nodes.
>>
>> Am I missing something important or is this just absolutely not what we
>> want?
> 
> Please see the thread:
> https://marc.info/?l=linux-kernel&m=163070220429222&w=2
> 
> Linus did not think it is a good choice to implement the "per-numa node page cache"

That doesn't make this approach any better.

I don't think we want this in the kernel. If user space wants to waste 
memory, it can happily mmap() however it wants. The advisory is to not 
do it.

-- 
Thanks,

David / dhildenb