linux-kernel - Re: [PATCH 0/3] Fix kdump failures with crashkernel=high

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Date:	Wed, 3 Dec 2014 11:35:06 +0100
From:	Joerg Roedel <jroedel@...e.de>
To:	WANG Chao <chaowang@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Fix kdump failures with crashkernel=high

Hi,

On Wed, Dec 03, 2014 at 12:01:23PM +0800, WANG Chao wrote:
>>From your experience It seems like swiotlb isn't working well with
> crashkernel=X,high alone. What about using crashkernel=X,low with
> crashkernel=X,high? Is there any reason you have to use
> crashkernel=X,high alone?

Sure, when I specify an additional crashkernel=X,low then I can get
things to work this way too. But my patch-set is about changing the
default, since the failure was seen on common server systems with the
defaults.

> crashkernel=X,high shouldn't automatically reserve 72M low at the first
> place. Now it's going insane if you increase it to 256M by default.

How should a kernel without some low memory (which has only memory above
4G available) handle any 32bit DMA devices? There would be no way to
allocate DMA-able memory for those devices.

And as I said, if people prefer it I can change the patch-set so that
the amount of low-memory allocated is subtracted from the amount of
high-memory. This way the overall memory usage for kdump would stay the
same while changing the defaults to work on more systems.

	Joerg

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