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Message-ID: <4A7A9E54.60705@redhat.com>
Date: Thu, 06 Aug 2009 17:11:48 +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>,
Andi Kleen <andi@...stfloor.org>
Subject: Re: [Patch 0/7] Implement crashkernel=auto
Eric W. Biederman wrote:
> Amerigo Wang <amwang@...hat.com> writes:
>
>> Yes, exactly, in fact I am doing another part which will allow us to take back
>> of the reserved memory at run-time.
>>
>
> Alright. Let's look at that.
>
> I would make the restriction you can't resize the area while a kexec
> on panic image is loaded, and growing the area would not be a
> realistic option.
>
>
Sure, I have no plan to do growing reserved memory at run-time... only
freeing or shrinking it...
> If crash_kernel=auto happens in the context of being able to shrink
> the area from user space the definition is simple. We reserve as much
> memory as we think we can without affecting performance, stability,
> reliability.
>
> We can use an initial approximation of perhaps 1/32nd of low memory
> (aka directly mapped memory), and I don't see a point in making the
> code arch dependent at all. We should run the size approximation past
> the folks on linux-mm as they are more likely to know how much memory
> reduction we can tolerate without problems.
>
>
Yup, agreed.
> We can then plan on user space saying hey that is more than I need:
> shrink that, and load the kexec on panic kernel.
>
Exactly... but the interface still needs to be discussed...
Currently, we have two options:
1) add a new flag to kexec_load(2) to tell the kernel to shrink the memory;
2) use /proc/iomem, let the user to decide which and how much of the
reserved memory should be removed.
Any thoughts?
Thanks.
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