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Subject: Re: why does "mem auto-init: clearing system memory may take some
 time..." takes about 14 sec under 5.4.17 but only few msec under 5.5.1?
To:     =?UTF-8?Q?Toralf_F=c3=b6rster?= <toralf.foerster@gmx.de>,
        Linux Kernel <linux-kernel@vger.kernel.org>
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From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <011e98b7-e73d-99e3-d0e7-5b68f89636bf@infradead.org>
Date:   Thu, 2 Apr 2020 18:33:24 -0700
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On 3/30/20 2:12 AM, Toralf Förster wrote:
> On 3/30/20 4:55 AM, Randy Dunlap wrote:
>> Hi > Toralf,
>>
>> Curious/odd.
>>
>> Do you have the kernel .config files for 5.4.17 and 5.5.1?
>> Looks like it would have to be a config difference AFAICT.
> 
> Sry,
> 
> attached the wrong configs at my previous mail. Here are 2 configs from the affected server attached.

Hi Toralf,

There's not much difference in the kernel config files, although
the one for 5.5.8 does have CONFIG_DEBUG_KERNEL=y while it's not set
in 5.4.17.

I built both kernels and booted them. I don't see a big time difference
like you reported.  Here's what I get:

5.4.17:

[    0.112274] mem auto-init: stack:off, heap alloc:on, heap free:on
[    0.112275] mem auto-init: clearing system memory may take some time...
[    0.621019] Memory: 3935312K/4095412K available (10243K kernel code, 1427K rwdata, 1924K rodata, 968K init, 768K bss, 160100K reserved, 0K cma-reserved)

and 5.5.8:

[    0.114455] mem auto-init: stack:off, heap alloc:on, heap free:on
[    0.114456] mem auto-init: clearing system memory may take some time...
[    0.622989] Memory: 3933200K/4095412K available (12291K kernel code, 1438K rwdata, 1952K rodata, 964K init, 708K bss, 162212K reserved, 0K cma-reserved)

but then a lot of the timestamps in your 5.5.8 log are 0.

-- 
~Randy