linux-kernel - Re: [RFC Patch 1/2] kexec: show memory info in /proc/iomem

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Message-ID: <m1eirhlryf.fsf@fess.ebiederm.org>
Date:	Tue, 11 Aug 2009 18:51:52 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	Neil Horman <nhorman@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, akpm@...ux-foundation.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC Patch 1/2] kexec: show memory info in /proc/iomem

Amerigo Wang <amwang@...hat.com> writes:

>> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>>
>> We can inspect the image we are going to load to get this information.
>> In fact /sbin/kexec already inspects the image we are going to load
>> to get this information.  Putting this in the kernel adds kernel
>> complexity for no gain.
>>   
>
> /sbin/kexec is supported to know this, of course. But this is not for
> /sbin/kexec, this is for user (or other programs) to observe the memory
> information, so that he can know the memory he reserved is too much or not.

> Without this, it is a little hard to use patch 2/2.

So add on option to /sbin/kexec.

Furthermore none of this does a good job of predicting how much
memory /sbin/fsck will require to check the filesystem before we
write a crash dump.

The only way I know of reliably obtaining that kind of information is
testing your crash userspace with different amounts of memory and
understanding what is going on.

Eric
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