Description of problem:
The crashkernel=auto detection algorithm bails out on systems with less than 4GB of memory, leading to the remove of the whole crashkernel=auto command line parameter.

The algorithm shouldn't force any artificial boundaries, instead it should try it's best to get kdump working. So instead of bailing out in the case of <4GB main memory it should just return the default of 128MB. If the system cannot allocate the memory it's going to complain anyway.

kernel/kexec.c
unsigned long long __init arch_default_crash_size(unsigned long long total_size)
{
        if (total_size < KEXEC_AUTO_THRESHOLD)
                return 0;
include/asm-generic/kexec.h
#define KEXEC_AUTO_THRESHOLD (1ULL<<32) /* 4G */

Also the kernel command line should be preserved the way it is. Tempering with it is usually a bad idea. It also conceals the reason why no memory gets reserved in this scenario.

static void __init reserve_crashkernel(void)
[...]
                        /*
                         * We can't reserve memory auotmatcally,
                         * remove "crashkernel=auto" from cmdline.
                         */
                        ck_cmdline += 4; /* strlen("auto") */
                        memmove(ck_cmdline - 16, ck_cmdline,
                                strlen(cmdline) - (ck_cmdline - cmdline) + 1);
                        return -ENOMEM;



Version-Release number of selected component (if applicable):
2.6.32-37.el6.i686