Messages in this thread | | | From | Ulrich Weigand <> | Subject | Re: [PATCH] s390 (5/7): kmalloc arguments. | Date | Fri, 7 Mar 2003 22:13:23 +0100 (MET) |
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Pete Zaitcev wrote:
>What does GFP_DMA do on s390 and s390x?
On s390, nothing.
On s390x, it makes sure the allocated memory resides at addresses below 2 GB. This is necessary, as many of the I/O subsystem data structures as defined by the hardware contain pointer fields that are still 31-bit, even on 64-bit machines. Thus we have to make sure those data structures are allocated below 2 GB. Using the GFP_DMA mechanism for that purpose seemed to be the way to go ...
Note that contrary to the usual purpose of GFP_DMA on Intel, the actual *data* that is being transferred via the I/O subsystem can reside at arbitrary addresses (which are specified via indirect-addressing lists); it is only the control data structures that need to go below 2 GB.
Bye, Ulrich
-- Dr. Ulrich Weigand weigand@informatik.uni-erlangen.de - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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