Messages in this thread | | | Date | Mon, 26 Jun 2006 14:22:20 +0100 (IST) | From | Mel Gorman <> | Subject | Re: 2.6.17-mm1 |
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On Mon, 26 Jun 2006, Franck Bui-Huu wrote:
> Mel Gorman wrote:
>>>> Not all arches will use init_bootmem(). Arm for example uses >>>> init_bootmem_node(). ARCH_PFN_OFFSET is only meant to affect mem_map, >>>> >>> well, I don't agree here. ARCH_PFN_OFFSET is used to save the first >>> page number that has physical memory. I don't see why we couldn't >>> useit to correctly initialise the memory system... >> >> Architectures will not always have a known fixed start of physical >> memory. On IA64 at least, they initialise memory as if it starts at 0 >> but on my one test machine, the beginning part is always a memory hole. > > in that case ARCH_PFN_OFFSET is 0 which is the old behaviour, nothing > change... >
The change is that ARCH_PFN_OFFSET has a slightly different meaning when you alter those two initialisation functions. Currently it is used to offset memmap from NODE_DATA(0)->node_start_pfn. By changing free_area_init() and init_bootmem(), it changes to altering the value of NODE_DATA(0)->node_start_pfn but only when memory is initialised in a particular way. I believe it makes ARCH_PFN_OFFSET even more obscure than it currently is.
I think we should just fix the problem at hand now for which two simple patches have been posted and consider making further changes to free_area_init() and init_bootmem() as a separate issue.
>> I've seen nothing to indicate that this hole will be the same size on >> all IA64 machines but I kinda doubt it. Also, arches that use >> init_bootmem() do not necessary use free_area_init(). >> > > but in that case do they use ARCH_PFN_OFFSET != 0 ?
IA64 do not and I didn't check all arches.
> if so that would be > very surprising. That would meand "I have a hole a the start of my mem, > I don't know at compile time where it starts, but I state that my physical > mem start at ARCH_PFN_OFFSET anyways" > >>> If we don't change init_bootmem() to use ARCH_PFN_OFFSET, then the >>> kernel will initialise the start of memory to 0 which is boggus. >>> IOW, >>> we can't use this function without this change (except if your memory >>> start at 0 of course). And I think that init_bootmem() has been >>> implemented for systems which have only one node _whatever_ memory >>> start value... >>> >> >> While you may be right, it'll only fix the problem for arches with >> ARCH_PFN_OFFSET and using init_bootmem (which is the case of MIPS I >> guess). But arches using init_bootmem_node or not using free_area_init() >> may still get kicked. >> > > Again in these cases, I doubt that they will setup ARCH_PFN_OFFSET... >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - 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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