slow boot with 7fef431be9c9 ("mm/page_alloc: place pages to tail in __free_pages_core()")
David Hildenbrand
david at redhat.com
Fri Mar 12 14:12:03 UTC 2021
On 12.03.21 15:06, Deucher, Alexander wrote:
> [AMD Public Use]
>
>> -----Original Message-----
>> From: David Hildenbrand <david at redhat.com>
>> Sent: Thursday, March 11, 2021 10:03 AM
>> To: Deucher, Alexander <Alexander.Deucher at amd.com>; linux-
>> kernel at vger.kernel.org; amd-gfx list <amd-gfx at lists.freedesktop.org>;
>> Andrew Morton <akpm at linux-foundation.org>
>> Cc: Huang, Ray <Ray.Huang at amd.com>; Koenig, Christian
>> <Christian.Koenig at amd.com>; Liang, Liang (Leo) <Liang.Liang at amd.com>;
>> Mike Rapoport <rppt at linux.ibm.com>; Rafael J. Wysocki
>> <rafael at kernel.org>; George Kennedy <george.kennedy at oracle.com>
>> Subject: Re: slow boot with 7fef431be9c9 ("mm/page_alloc: place pages to
>> tail in __free_pages_core()")
>>
>> On 11.03.21 15:41, Deucher, Alexander wrote:
>>> [AMD Public Use]
>>>
>>> Booting kernels on certain AMD platforms takes 2-3 minutes with the patch
>> in the subject. Reverting it restores quick boot times (few seconds). Any
>> ideas?
>>>
>>
>> Hi,
>>
>> We just discovered latent BUGs in ACPI code whereby ACPI tables are
>> exposed to the page allocator as ordinary, free system RAM. With the
>> patch you mention, the order in which pages get allocated from the page
>> allocator are changed - which makes the BUG trigger more easily.
>>
>> I could imagine that someone allocates and uses that memory on your
>> platform, and I could imagine that such accesses are very slow.
>>
>> I cannot tell if that is the root cause, but at least it would make sense.
>>
>> See
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.
>> kernel.org%2Fpatchwork%2Fpatch%2F1389314%2F&data=04%7C01%7C
>> alexander.deucher%40amd.com%7Cd1533aaddccd464c59f308d8e49ec563%7
>> C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637510717893096801%
>> 7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLC
>> JBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=xpty77D54Z5S%2FKK
>> JO5SsVQaNsHoojWMR73whpu8VT%2B4%3D&reserved=0
>>
>> You might want to give that patch a try (not sure if it's the latest
>> version). CCing George
>
> Thanks for the patch. Unfortunately it didn't help. Any other ideas? Is there a newer version of that patch?
>
@George?
It's interesting that this only applies to these special AMD systems so
far. Is there anything particular about these systems? How much memory
do these systems have?
Increasing the boot time from a few seconds to 2-3 minutes does not
smell like some corner case cache effects we might be hitting in this
particular instance - there have been minor reports that it either
slightly increased or slightly decreases initial system performance, but
that was about it.
Either, yet another latent BUG (but why? why should memory access
suddenly be that slow? I could only guess that we are now making sooner
use of very slow memory), or there is really something else weird going on.
Cheers!
> Alex
--
Thanks,
David / dhildenb
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