linux-kernel - Re: slow boot with 7fef431be9c9 ("mm/page_alloc: place pages to tail in __free_pages

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Date:   Tue, 16 Mar 2021 09:37:48 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Liang, Liang (Leo)" <Liang.Liang@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>
Cc:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Huang, Ray" <Ray.Huang@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        George Kennedy <george.kennedy@...cle.com>
Subject: Re: slow boot with 7fef431be9c9 ("mm/page_alloc: place pages to tail
 in __free_pages_core()")

On 16.03.21 09:00, Liang, Liang (Leo) wrote:
> [AMD Public Use]
> 
> Hi Mike,
> 
> Thanks for help. The patch works for me and boot time back to normal. So it's a fix, or just WA?

Hi Leo,

excluding up to 16 MiB of memory on every system just because that 
single platform is weird is not acceptable.

I think we have to figure out

a) why that memory is so special. This is weird.
b) why the platform doesn't indicate it in a special way. Why is it 
ordinary system RAM but still *that* slow?
c) how we can reliably identify such memory and exclude it.

I'll have a peek at the memory layout of that machine from boot logs 
next to figure out if we can answer any of these questions.

Just to verify: this does happen on multiple machines, not just a single 
one? (i.e., we're not dealing with faulty RAM)

-- 
Thanks,

David / dhildenb