How to allocate a block of 16MB in kernel space using my driver module

s_anumolu · 07-14-2005, 11:22 PM

Hi all,
I am new to device driver programming and working on linux 2-4-20. I have tried to allcoate 16MB block in kernel space with get_free_pages(), kmalloc(), kmem_cache_create().; I am not able to allocate more than 2Mb though used the GFP_USER or with GFP_KERNEL flags. I could not do more than that , as per their limitations in allocation. Can any one please help me in this issue.
Thanks
sudheer

foo_bar_foo · 07-15-2005, 12:48 AM

yes it's very hard to get a concurrent DMA buffer larger than 128 KB at runtime
i think it's because the memory gets fragmented
you can keep digging at the same area with kmalloc(GFP_ATOMIC)
but that seems like pretty risky buisness to me
download the samples here
http://examples.oreilly.com/linuxdrive2/
and check out the folder allocator

i don't know that much about it or what you are doing but there is a driver I/O abstraction layer
struct kiobuf from <linux/iobuf.h>
you can allocate a vector of buffers

Code:

int alloc_kiovec(int nr, struct kiobuf **iovec);

it allows you to ignore the underlying vm junk
or for block devices you got the kernel file
./drivers/char/raw.c
where you really don't go through the kernel at all