User allocated memory for DMA

Benjamin Herrenschmidt benh at
Wed Dec 8 15:45:17 EST 2004

On Wed, 2004-12-08 at 09:19 +0530, Amit K Tiwari wrote:
> Thanks, it helped a lot.
> Here is what works - 
> 1. Increase the shared memory limit (sysctl kernel.shmmax)
> 2. Configure the large pages (echo 256 > /proc/sys/vm/nr_hugepages)
> 3. Use shmget to get a handle to huge pages - Set the  SHM_HUGETLB
> bits in flags.

Still, user pages beeing mapped in wrong order is a bit worrying... I
may be fixed in more recent kernels, or not, I'd rather do some


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