linux-kernel - Re: [PATCH] kdump: add default crashkernel reserve kernel config options

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Message-ID: <20180524110241.3f60997c@ezekiel.suse.cz>
Date:   Thu, 24 May 2018 11:02:41 +0200
From:   Petr Tesarik <ptesarik@...e.cz>
To:     Dave Young <dyoung@...hat.com>
Cc:     dzickus@...hat.com, Neil Horman <nhorman@...hat.com>,
        Tony Luck <tony.luck@...el.com>, bhe@...hat.com,
        Michael Ellerman <mpe@...erman.id.au>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] kdump: add default crashkernel reserve kernel config
 options

On Thu, 24 May 2018 15:26:27 +0800
Dave Young <dyoung@...hat.com> wrote:

> On 05/24/18 at 08:57am, Petr Tesarik wrote:
>[...]
> > What is "a very minimal initrd"? Last time I had to make a significant
> > adjustment to the estimation for openSUSE, this was caused by growing
> > user-space requirements (systemd in this case, but I don't want to
> > start flamewars on that topic, please).  
> 
> Still I think we have agreement and same feeling about the userspace
> memory requirement.   I think although it is hard, we have been still
> trying to shrink the initramfs memory use.
> 
> Besides of distribution use,  why people can not use some minimal
> initrd?  For example only a basic shell and some necessary tools and
> basic storage eg. raw disks supported, and he/she can just collect the
> panic infomation by himself in a shell.

Again, I'm having trouble with the definition of a "minimal initrd" and
also with the definition of a "workstation". I have already seen a sad
case where kdump started going OOM after connecting a 4K monitor,
because, well, it needed a bigger framebuffer...

OTOH you wrote in another mail that RH has tested some values on a
variety of hardware, so you seem to have a clue. Good for you. I still
believe it is moving policy into the kernel.

Based on past experience, I expect that certain users will argue that
"crashkernel=auto" should work out of the box on their HPE Superdome
with 600+ LUNs attached...

As you wrote elsewhere in the thread:

> I means this patch is not trying to force add a fixed value for crashkernel
> in kernel code. It provides another way one can use on kernel build time
> the value just works.

I don't mind if it is added, although I don't find it very useful.

Petr T