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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Fri, 20 Oct 2023 10:46:34 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Qi Zheng <zhengqi.arch@bytedance.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@suse.com>, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2] x86/mm: Drop 4MB restriction on minimal NUMA node
 memory size
Message-ID: <ZTI+aiL/eKGbem6G@gmail.com>
References: <20231017062215.171670-1-rppt@kernel.org>
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* Qi Zheng <zhengqi.arch@bytedance.com> wrote:

> Hi Ingo,
> 
> On 2023/10/18 20:44, Ingo Molnar wrote:
> > 
> > * Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> > 
> > > > While I agree with dropping the limitation, and I agree that
> > > > 9391a3f9c7f1 should have provided more of a justification, I believe a
> > > > core MM fix is in order as well, for it to not crash. [ If it's fixed
> > > > upstream already, please reference the relevant commit ID. ]
> > > 
> > > Agree. I posted a fixed patchset[1] before, maybe we can reconsider it.
> > > :)
> > > 
> > > [1]. https://lore.kernel.org/lkml/20230215152412.13368-1-zhengqi.arch@bytedance.com/
> > > 
> > > For memoryless node, this patchset skip it and fallback to other nodes
> > > when build its zonelists.
> > 
> > Mind resubmitting that to the MM folks, with the NULL dereference crash
> > mentioned prominently? Feel free to Cc: me.
> 
> OK, I will resend it if no one else objects. :)

Thanks, much appreciated - and I see Andrew already applied your two fixes 
to -mm.

With that background I was able to apply the x86 fix as well - which can be 
backported without the MM changes. The current commit in tip:x86/mm is:

  a1e2b8b36820 ("x86/mm: Drop the 4 MB restriction on minimal NUMA node memory size")

Which should hit v6.7 in about ~1.5 weeks, unless there's unexpected 
problems.

Thanks,

	Ingo