Vitaly Mayatskikh <v.mayatskih at gmail.com> writes: > Patch applies to 2.6.34-rc5 > > On x86 platform, even if hardware is 64-bit capable, kernel starts > execution in 32-bit mode. When system is kdump-enabled, crashed kernel > switches to 32 bit mode and jumps into new kernel. This automatically > limits location of dump-capture kernel image and it's initrd by first > 4Gb of memory. Switching to 32 bit mode is performed by purgatory > code, which has relocations of type R_X86_64_32S (32-bit signed), and > this cuts "good" address space for crash kernel down to 2 Gb. I/O > regions may cut down this space further. > > When system has a lot of memory (hundreds of gigabytes), dump-capture > kernel also needs relatively a lot of memory to account old kernel's > pages. It may be impossible to reserve enough memory below 2 or even 4 > Gb. Simplest solution is it break dump-capture kernel's reserved > memory region into two pieces: first (small) region for kernel and > initrd images may be easily placed in "good" address space in the > beginning of physical memory, and second region may be located > anywhere. > > This serie of patches realizes this approach. It requires also changes > in kexec utility to make this feature work, but is > backward-compatible: old versions of kexec will work with new > kernel. I will post patch to kexec-tools upstream separately. Have you tried loading a 64bit vmlinux directly into a higher address range? There may be a bit or two missing but you should be able to load a linux kernel above 4GB. I tested the basics of that mechanism when I made the 64bit relocatable kernel. I don't buy the argument that there is a direct connection between the amount of memory you have and how much memory it takes to dump it. Even an indirect connections seems suspicious. Eric
