How to allocate LARGE (more than 16M) DMA memory?

leechaotang · 10-04-2011, 01:54 AM

Hi,

In Fedora 15, how I allocate LARGE (more than 16M) DMA memory? My device is PCIe bus.

I try the dma_alloc_coherent and pci_alloc_consistent, it seems the two functions can not work more than 4M.

What kernel parameter(s) can let me allocate LARGE DMA memory?

Thanks!

syg00 · 10-04-2011, 02:07 AM

Dma32 ?

leechaotang · 10-04-2011, 02:13 AM

Hi,

I did more test, I can allocate 4M for 4 times successfully but can not allocate a 16M .....

Why? Anything I can configure the Linux ...

robvoo · 10-05-2011, 06:04 AM

Hi try this: cat /proc/buddyinfo

It will display how manyblocks are available at which NUMA node.
Look on the internet on how to interpretate the data.
The right most numbers are the 4MB DMA blocks.

After a fresh reboot the most 4MB blocks are available, don't
know if a function exists to gather smaller blocks into a large one
look at these links:

http://lwn.net/Articles/211505/
http://puschitz.com/pblog/?p=28