netdev - Re: [PATCH bpf 0/4] introduce HAVE_ARCH_HUGE_VMALLOC_FLAG for bpf_prog

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Message-ID: <F3447905-8D42-46C0-B324-988A0E4E52E7@fb.com>
Date:   Thu, 31 Mar 2022 23:59:56 +0000
From:   Song Liu <songliubraving@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Song Liu <song@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "pmenzel@...gen.mpg.de" <pmenzel@...gen.mpg.de>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH bpf 0/4] introduce HAVE_ARCH_HUGE_VMALLOC_FLAG for
 bpf_prog_pack

Hi Christoph, 

> On Mar 30, 2022, at 10:37 PM, Christoph Hellwig <hch@...radead.org> wrote:
> 
> On Wed, Mar 30, 2022 at 03:56:38PM -0700, Song Liu wrote:
>> We prematurely enabled HAVE_ARCH_HUGE_VMALLOC for x86_64, which could cause
>> issues [1], [2].
>> 
> 
> Please fix the underlying issues instead of papering over them and
> creating a huge maintainance burden for others.

I agree that this set is papering over the issue. And I would like 
your recommendations here. 

The biggest problem to me is that we (or at least myself) don't know 
all the issues HAVE_ARCH_HUGE_VMALLOC will trigger on x86_64. Right 
now we have a bug report from Paul, and the warning from Rick, but
I am afraid there might be some other issues. 

How about we approach it like this:

Since it is still early in the release cycle (pre rc1), we can keep 
HAVE_ARCH_HUGE_VMALLOC on for x86_64 for now and try to fix all the 
reported issues and warnings. If things don't go very well, we can
turn HAVE_ARCH_HUGE_VMALLOC off after rc4 or rc5. 

Does this make sense?

Thanks,
Song