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

From: Joerg Roedel
Date: Wed Dec 03 2014 - 05:35:16 EST


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

> 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.


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