Re: DMA memory limitation?

From: Alan Cox (
Date: Thu Jul 05 2001 - 06:53:45 EST

> Is there any limitation on DMA memory we can allocate using
> kmalloc(size, GFP_DMA)? I am not able to acquire more than
> 14MB of the mem using this on my PCI SMP box with 256MB ram.
> I think there is restriction on ISA boards of 16MB.

Yes. GFP_DMA allocates memory below 16Mbytes for ISA devices and that is
a physical wiring issue. For PCI devices you can allocate a lot more using
the pci_alloc_* and pci_map_* interface to allocate memory for PCI in a
CPU independant manner. It'll also then look after cache coherency issues
for you

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Sat Jul 07 2001 - 21:00:15 EST