[kbuild-devel] A hole in kernel space!

[Pannaga Bhushan]

Hi all,
        I am looking for a setup where I need to have a certain amount of data always available to the kernel. The size of data I am looking at is abt 40MB(preferably, but I will settle for 20MB too) . So the normal kmalloc will not help me. So what I did was, I created a hole in kernel space by putting the following line in vmlinux.lds

    ALIGN(4096);
 __hole_start = .;
    . = . + 0xmy_size;
 __hole_end = .;

First, I put these lines in code segment and found that  'my_size' cannot go beyond 0x500000(5MB) . Any larger value , the kernel image refuses to boot up. I found the same problem with these lines being in data segment or in the bss segment.

But putting these line after

_end = .;

line in vmlinux.lds, I am able to give 0x1700000(17MB) to my_size and still boot with that kernel image.

My questions are :

1.   Is there any other way I can get to keep 40MB(or even 20MB) of contiguous kernel memory space ?

2.    Abt the 17MB hole, I am able to use after the   _end = .;   ....     is this 17MB really there in kernel image?('cos it isn't in any segment and also it appears after _end).
        if yes, are the pages corresponding to this region swappable or is it that since this hole appears in kernel image, it is locked to a physical space and this is never swapped. (basically, i want by data in kernel space always available to kernel without having to bother abt swapping the pages back)

Thanx in advance,
Pannaga Bhushan