Messages in this thread | | | Date | Thu, 2 May 2002 18:40:37 +0200 | From | Andrea Arcangeli <> | Subject | Re: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?] |
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On Thu, May 02, 2002 at 09:10:00AM -0700, Martin J. Bligh wrote: > > You can trivially map the phys mem between 1G and 1G+256M to be in a > > direct mapping between 3G+256M and 3G+512M, then you can put such 256M > > at offset 1G into the ZONE_NORMAL of node-id 1 with discontigmem too. > > > > The constraints you have on the normal memory are only two: > > > > 1) direct mapping > > 2) DMA > > > > so as far as the ram is capable of 32bit DMA with pci32 and it's mapped > > in the direct mapping you can put it into the normal zone. There is no > > difference at all between discontimem or nonlinear in this sense. > > Now imagine an 8 node system, with 4Gb of memory in each node. > First 4Gb is in node 0, second 4Gb is in node 1, etc. > > Even with 64 bit DMA, the real problem is breaking the assumption > that mem between 0 and 896Mb phys maps 1-1 onto kernel space. > That's 90% of the difficulty of what Dan's doing anyway, as I > see it.
You don't need any additional common code abstraction to make virtual address 3G+256G to point to physical address 1G as in my example above, after that you're free to put the physical ram between 1G and 1G+256M into the zone normal of node 1 and the stuff should keep working but with zone-normal spread in more than one node. You just have full control on virt_to_page, pci_map_single, __va. Actually it may be as well cleaner to just let the arch define page_address() when discontigmem is enabled (instead of hacking on top of __va), that's a few liner. (the only true limit you have is on the phys ram above 4G, that cannot definitely go into zone-normal regardless if it belongs to a direct mapping or not because of pci32 API)
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