On Mon, Jul 09, 2007 at 11:08:02AM +0200, Lukas Hejtmanek wrote: > On Sun, Jul 08, 2007 at 10:03:16PM -0700, Roland Dreier wrote: > > Is the memory given to a domU always physically contiguous? If not, > > what happens when a domU kernel does alloc_pages(GFP_KERNEL, 6) to try > > and allocate 256 KB or something like that. Let's assume that the > > domU kernel has enough guest contiguous pages to satisfy the > > allocation -- is there any guarantee that the pages are really > > physically contiguous? > > according to Xen-dev alloc_pages does *not* guarantee contiguous > pages. They say that the pci_alloc_consistent should be used > instead. The question is whether non-Xen kernel *usually* allocates > contiguous pages and so far it has been working and whether it > should be fixed in the mainline of the driver. > > I do some tests (and also try to figure out how to change > alloc_pages to pci_alloc_consistent) to verify contiguous pages.
You missed an important bit of Keir's response---it's perfectly fine to use alloc_pages provided you then use the dma_map_single API, which for Xen dom0 will take care of bounce-buffering to a machine-contiguous buffer if necessary. I am not sure if the same holds for a domU kernel. Cheers, Muli _______________________________________________ general mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
