(add linux-mm) On Wed, 29 Nov 2006 10:34:24 -0800 "Luck, Tony" <tony.luck@xxxxxxxxx> wrote: > > After some investigations I stated that count_node_pages() was computing > > mem_data[1].min_pfn = 0, and mem_data[1].max_pfn = 20000 for node 1, > > thus conflicting with the 0-2GB DMA memory range on node 0. > > This is due to the line: > > start = ORDERROUNDDOWN(start); > > There is an assumption here that the memory space on a node doesn't > cross a MAX_ORDER boundary ... and I'm not really sure where to go > with that. Your patch papers over the problem for your specific case, > but as you point out it will just re-appear for someone who picks > a bigger MAX_ORDER. > > Having nodes that are smaller than MAX_ORDER will cause confusion in > the allocator (if all the memory belonging to two nodes is in a > single MAX_ORDER page, the buddy allocator will give all the memory > to one node, and none to the other (won't it?). > > > This should at least be checked in the count_node_pages() function. > > Yes, a check should be made ... but count_node_pages() doesn't have > all the information if needs to do this (it just gets the start/size > for the memory on the node ... and it needs to check whether the > rounddown of the start address (or the roundup of the end address) > would cause conflicts with memory belonging to other nodes. > > Do we need a "max_order" variable that could be adjusted to some lower > value that MAX_ORDER if we find the memory topology doesn't fit inside > the lines? > (Your email talks about nodes, but I am asuming that we're actually dealing with per-zone concepts here) We could of course do that, although it looks like your runtime max_order should be per-zone and not global. And making it a runtime thing would cause more code to be emitted for alloc_pages() and alloc_pages_node(), so we'd at least have to move their checks into .c. But I wonder if a better approach would be to teach ia64 to just throw away the last 1 .. MAX_ORDER-1 pages from the oddball zone? - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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