From: ebiederm@xmission.com (Eric W. Biederman)
To: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Cc: Cong Wang <amwang@redhat.com>,
Neil Horman <nhorman@tuxdriver.com>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
Haren Myneni <hbabu@us.ibm.com>, Ingo Molnar <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH 0/5] Add second memory region for crash kernel
Date: Thu, 22 Apr 2010 15:07:11 -0700 [thread overview]
Message-ID: <m1aasvkupc.fsf@fess.ebiederm.org> (raw)
In-Reply-To: <1271953392-6324-1-git-send-email-v.mayatskih@gmail.com> (Vitaly Mayatskikh's message of "Thu\, 22 Apr 2010 18\:23\:07 +0200")
Vitaly Mayatskikh <v.mayatskih@gmail.com> writes:
> Patch applies to 2.6.34-rc5
>
> On x86 platform, even if hardware is 64-bit capable, kernel starts
> execution in 32-bit mode. When system is kdump-enabled, crashed kernel
> switches to 32 bit mode and jumps into new kernel. This automatically
> limits location of dump-capture kernel image and it's initrd by first
> 4Gb of memory. Switching to 32 bit mode is performed by purgatory
> code, which has relocations of type R_X86_64_32S (32-bit signed), and
> this cuts "good" address space for crash kernel down to 2 Gb. I/O
> regions may cut down this space further.
>
> When system has a lot of memory (hundreds of gigabytes), dump-capture
> kernel also needs relatively a lot of memory to account old kernel's
> pages. It may be impossible to reserve enough memory below 2 or even 4
> Gb. Simplest solution is it break dump-capture kernel's reserved
> memory region into two pieces: first (small) region for kernel and
> initrd images may be easily placed in "good" address space in the
> beginning of physical memory, and second region may be located
> anywhere.
>
> This serie of patches realizes this approach. It requires also changes
> in kexec utility to make this feature work, but is
> backward-compatible: old versions of kexec will work with new
> kernel. I will post patch to kexec-tools upstream separately.
Have you tried loading a 64bit vmlinux directly into a higher address
range? There may be a bit or two missing but you should be able to
load a linux kernel above 4GB. I tested the basics of that mechanism
when I made the 64bit relocatable kernel.
I don't buy the argument that there is a direct connection between
the amount of memory you have and how much memory it takes to dump it.
Even an indirect connections seems suspicious.
Eric
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next prev parent reply other threads:[~2010-04-22 22:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-22 16:23 [PATCH 0/5] Add second memory region for crash kernel Vitaly Mayatskikh
2010-04-22 16:23 ` [PATCH 1/5] Introduce second memory resource " Vitaly Mayatskikh
2010-04-22 16:23 ` [PATCH 2/5] Modify parse_crashkernel* for new syntax Vitaly Mayatskikh
2010-04-22 16:23 ` [PATCH 3/5] Support second memory region in crash_shrink_memory() Vitaly Mayatskikh
2010-04-22 16:23 ` [PATCH 4/5] x86: use second memory region for dump-capture kernel Vitaly Mayatskikh
2010-04-22 16:23 ` [PATCH 5/5] kexec: update documentation Vitaly Mayatskikh
2010-04-22 22:07 ` Eric W. Biederman [this message]
2010-04-22 22:37 ` [PATCH 0/5] Add second memory region for crash kernel H. Peter Anvin
2010-04-22 22:45 ` Vivek Goyal
2010-04-23 0:48 ` Eric W. Biederman
2010-04-23 5:21 ` Cong Wang
2010-04-23 5:42 ` Eric W. Biederman
2010-04-23 6:43 ` Vitaly Mayatskikh
2010-04-23 14:44 ` Vivek Goyal
2010-04-23 7:08 ` Vitaly Mayatskikh
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