Proposal for run time memory allocation for crash kernel

[Ronit halder]

Hi,
Currenty linux kernel allocates memory at the boot time for crash
kernel booted using kexec system call in kernel crash. It will be very
useful if we can allocate memory in run time.
It is possible to allocate memory for crash kernel at the boot time
using CMA (Contiguous Memory Allocator). CMA is capable of allocating
big chunk of memory. At the boot time we will create one (if only low
memory is used) or two (if we use both high and low memory) CMA areas
of size given in "crashkernel" boot time command line parameter. Then
the user can allocate or free memory from those CMA areas using
"/sys/kernel/kexec_crash_size" sysfs entry.

I am attaching a prototype patch with the mail. I have made the patch
against kernel version v4.4.11.
Please give your opinions.
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