On Wed, Apr 26, 2006 at 11:28:02AM -0700, Randy.Dunlap wrote: > On Wed, 26 Apr 2006 14:11:08 -0400 Vivek Goyal wrote: > > > On Wed, Apr 26, 2006 at 10:49:35AM -0700, David Wilder wrote: > > > > > > 2) On x86, enable high memory support under "Processor type and > > > features": > > > > > > CONFIG_HIGHMEM=y > > > > I think it should be changed to CONFIG_HIGHMEM64G=y > > Why? Lots of people won't care for that.
Kdump kernel uses the code under CONFIG_HIGHMEM to map the memory being used by the first kernel hence HIGHMEM support is required in second kernel. But it is not necessary to set CONFIG_HIGHMEM64G=y. User can very well choose CONFIG_HIGHMEM4G=y. I misunderstood the option. I thought that if first kernel had booted with memory more than 4G then second kernel would need CONFIG_HIGHMEM64G=y to access that memory. But grepping through the code, it looks like that this option enbales DMA to 64 bit addresses on 32 bit machines. And in this case DMA from/to that address is not required as after mapping the pfn, we copy the page to user space buffer which is in LOWMEM as second kernel is booted with just 64MB of memory. -vivek
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