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I am somewhat of a newbie to Linux apps / kernel / driver programming.
I have question related to kernel memory allocation which I am not able to clearly find an answer. I have Google'd around and found lot of incomplete threads without any solution. Here is what I have -
For x86_64 - Nehalem CPU 64 bit mode, I have a system with 6GB memory, with a PCIe device capable of performing 64 bit DMA.
I want to allocate 2GB or more of DMA memory via a kernel lkm module. Basically idea is to make memory allocation kernel aware.
1> Can the DMA memory beyond 4G address space be allocated by kernel ?
Are there any limitations with 2.6.x ?
2> I have a sample LKM which via an ioctl allocates memory using get_free_page, however after allocating around 65xxx pages (~256MB), the kernel OOM kicks in and kills the user process ? Is there a config anywhere to prevent his ? Is the user space process limited to certain amount memory ?
3> This is 64 bit mode kernel so technically there should be no restrictions right ? I am also aware about some of the allocate_bootmem options, but not quite clear on their usage for address space beyond 4Gb. Is this only choice ? What about DMA coherency ?
Thanks a bunch in advance.
Last edited by kd2000; 03-26-2010 at 05:20 PM.
Distribution: Debian squeeze (Gnome) on netbooks; Debian Lenny on servers and Debian wheezy (XFCE) on new laptops
As far as I know the 64 bits kernels all have a limit of 64GB and also the 32 bits BigMem kernels do, with the difference that applications will get a maximum of 3008MB per application in the 32 bits BigMem kernels and in the 64 bits they will have all memory available per process.
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