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

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Date:	Wed, 5 Aug 2009 10:04:08 -0400
From:	Neil Horman <nhorman@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Amerigo Wang <amwang@...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

On Wed, Aug 05, 2009 at 06:33:57AM -0700, Eric W. Biederman wrote:
> Amerigo Wang <amwang@...hat.com> writes:
> 
> > This series of patch implements automatically reserved memory for crashkernel,
> > by introducing a new boot option "crashkernel=auto". This idea is from Neil.
> >
> > In case of breaking user-space applications, it modifies this boot option after
> > it decides how much memory should be reserved.
> >
> > On different arch, the threshold and reserved memory size is different. Please
> > refer patch 7/7 which contains an update for the documentation.
> >
> > Note: This patchset was only tested on x86_64 with differernt memory sizes.
> 
> This seems like a silly hard code. Especially for a feature distros don't
> care enough about to implement a working initrd for.
> 
> Has anyone bothered to justify those large amounts of memory?
> Where does the 128M go?
> 
> Please pardon me for being a cynic but I don't see the command line option
> being the bottleneck for real users to make this work.
> 
> Eric

Lots of the impetus behind this results from a desire to have kexec configured
and setup up during install.  Having the kernel allocate a default size block of
RAM lets you do that without the need for an interim reboot.  You could of
course boot the installer kernel with a crashkernel line pre-selected  suppose,
but then you have to go to the trouble of figuring that allocation size out each
time.  This gives you a nice convienent way to get a reasonable block of memory
without the need to do all that extra work.
Neil

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