Messages in this thread | | | Date | Mon, 18 Mar 2013 14:14:28 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] x86, kdump: Set crashkernel_low automatically |
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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.
-hpa
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