Re: [PATCH] x86, kdump: Set crashkernel_low automatically

From: H. Peter Anvin
Date: Mon Mar 18 2013 - 17:17:16 EST

On 03/18/2013 01:00 PM, Vivek Goyal wrote:
> On Mon, Mar 18, 2013 at 12:10:47PM -0700, H. Peter Anvin wrote:
>> On 03/18/2013 08:33 AM, Vivek Goyal wrote:
>>> Thinking more about it, if ongoing DMA is an issue, then setting up
>>> software iotlb in those areas is also prone to being overwritten by
>>> those DMAs. Hence, reserving memory low where no DMA is setup by first
>>> kernel, seems somewhat safer.
>> Agreed. We really should reserve some memory low.
> So which approach do you like for reserving some memory low.
> - User specifies crashkernel_low=X to reserve some memory. Biggest problem
> here is how does user know how much memory is required for setting up
> swiotlb.
> - Take yinghai's patch where by default low memory for swiotlb is reserved
> and a user need to opt out of it using crashkernel_low=0 if system has
> iommu enabled.
> - crashkernel=X by default first looks for specified memory in low
> memory area.
> I kind of like yinghai's approach. It is little wasteful of memory when
> memory is reserved high but atleast user does not have know how much memory
> to reserve low it works both when memory is reserved low (system does
> not have any RAM mapped above 4G) and when memory is reserved high.

I would agree, I think it is the most user friendly.


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