linux-kernel - Re: [Patch 0/7] Implement crashkernel=auto

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Date:	Thu, 06 Aug 2009 11:39:23 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Neil Horman <nhorman@...hat.com>, linux-kernel@...r.kernel.org,
	tony.luck@...el.com, linux-ia64@...r.kernel.org,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	Anton Vorontsov <avorontsov@...mvista.com>
Subject: Re: [Patch 0/7] Implement crashkernel=auto

Eric W. Biederman wrote:
> In general I figure that whoever builds the kernel and initrd should be
> responsible for testing and figuring out the amount of memory needed.
> The primary kernel has no idea what is going to loaded in there and
> as such no real idea how much memory is needed.
>   

Yeah, that is exactly why I _didn't_ pick the idea of reserving memory 
automatically and silently without "crashkernel=auto".

If a user specifies "crashkernel=auto", that means he/she has no idea 
how much memory to be reserved, he/she wants to let the kernel to 
decide. Kernel should know better than the user in this situation.

>>> You also have to build (or at least load) the whole kdump image after
>>> the system boots, and configure someplace for this to be saved.
>>>
>>> What class of problems do you expect to catch with this?
>>>   
>>>       
>> Again, try to save the user from choosing numbers for "crashkernel=".
>>     
>
> The user being kernel developers?  Whoever builds the kernel and initrd
> should be responsible for testing and figuring this out.
>
> In a distro context installers etc should be able to setup good defaults
> so end users don't have to worry about this.
>
>   
For kernel developers, "crashkernel=auto" should save a lot. You seem 
agree with this one.

For users, they rely on the distro which can always specify 
"crashkernel=auto" now, not different numbers for different arch, since 
"crashkernel=auto" is designed to be safe for all cases. Also saves many 
work...

>>> What has me puzzled is that the mkdumprd that ships with fedora isn't
>>> usable without patching, and it seems to be steadily getting worse.  
>>>       
>> Please explain why it is not usable? The patch won't break the userspace, since
>> it modifies the "crashkernel=" command line dynamically.
>>     
>
> No the crashdump mechanism is useless because user space is already
> broken and unusable.

Again, why broken?

Thanks.


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