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

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Message-ID: <b5faa9b9-6f40-f8e4-cf7c-795b429e02a8@redhat.com>
Date:   Fri, 12 Mar 2021 16:48:28 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "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>,
        "Liang, Liang (Leo)" <Liang.Liang@....com>
Cc:     "Huang, Ray" <Ray.Huang@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        Mike Rapoport <rppt@...ux.ibm.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()")

> 8G (with some carve out for the integrated GPU).
> [    0.044181] Memory: 6858688K/7200304K available (14345K kernel code, 9659K rwdata, 4980K rodata, 2484K init, 12292K bss, 341360K reserved, 0K cma-reserved)
> 
> Nothing particularly special about these systems that I am aware of.  I'll see if we can repro this issue on any other platforms, but so far, not one has noticed any problems.
> 
>>
>> 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.
> 
> Looks like pretty much everything is slower based on the timestamps in the dmesg output.  There is a big jump here:

If we're really dealing with some specific slow memory regions and that 
memory gets allocated for something that gets used regularly, then we 
might get a general slowdown. Hard to identify, though :)

> 
>> [    3.758596] ACPI: Added _OSI(Linux-Lenovo-NV-HDMI-Audio)
>> [    3.759372] ACPI: Added _OSI(Linux-HPI-Hybrid-Graphics)
>> [   16.177983] ACPI: 13 ACPI AML tables successfully acquired and loaded
>> [   17.099316] ACPI: [Firmware Bug]: BIOS _OSI(Linux) query ignored
>> [   18.969959] ACPI: EC: EC started
> 
> And here:
> 
>> [   36.566608] PCI: CLS 64 bytes, default 64
>> [   36.575383] Trying to unpack rootfs image as initramfs...
>> [   44.594348] Initramfs unpacking failed: Decoding failed
>> [   44.765141] Freeing initrd memory: 46348K
> 
> Also seeing soft lockups:
>> [  124.588634] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [swapper/1:0]

Yes, I noticed that -- there is a heavy slowdown somewhere.

As that patch is v5.10 already (and we're close to v5.12) I assume 
something is particularly weird about the platform you are running on - 
because this is the first time I see a report like that.

-- 
Thanks,

David / dhildenb