Messages in this thread | | | Date | Tue, 18 Oct 2005 11:29:18 +0900 | From | Yasunori Goto <> | Subject | Re: [discuss] Re: x86_64: 2.6.14-rc4 swiotlb broken |
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Hello. Linus-san.
> NOTE! Even if the machine has 4GB or more of memory, it's entirely likely > that the quick "use NODE(0)" hack will work fine. > > Why? Because the bootmem memory should still be allocated low-to-high by > default, which means that as logn as NODE(0) has _enough_ memory in the > DMA range, we should be ok. > > So I _think_ the simple one-liner NODE(0) patch is sufficient, and should > work (and is a lot more acceptable for 2.6.14 than switching the node > ordering around yet again, or doing bigger surgery on the bootmem code). > > So the only thing that worried me (and made me ask whether there might be > machines where it doesn't work) is if some machines might have their high > memory (or no memory at all) on NODE(0). It does sound unlikely, but I > simple don't know what kind of strange NUMA configs there are out there. > > And I'm definitely only interested in machines that are out there, not > some theoretical issues.
In our making IA64 machine node 0 might not have any low-memory, and another node can have low-memory instead.
This cause comes from hotplug whole of one node. For example, please imagine following case.
1) In this case, firmware remembers pxm 1's node has low memory.
node 0 node 1 +--------------+ +-----------+ | pxm = 1 | | pxm = 2 | | low memory | | | +--------------+ +-----------+
2) If one node is hot-added at pxm = 0 (pxm is decided from physical locate by firmware.), new node will be node 2.
node 2 node 0 node 1 +-----------+ +--------------+ +-----------+ | pxm = 0 | | pxm = 1 | | pxm = 2 | | | | low memory | | | +-----------+ +--------------+ +-----------+
3) If user reboots the machine, Linux decides node id from pxm's order. But firmware still remembers which node has low memory. So, node 0 will not have any low memory.
node 0 node 1 node 2 +-----------+ +--------------+ +-----------+ | pxm = 0 | | pxm = 1 | | pxm = 2 | | | | low memory | | | +-----------+ +--------------+ +-----------+
So, just "use NODE(0)" is not enough hack for our machine. If "use NODE(0)" is selected, kernel must sort pgdat link and node id by memory address. I think that hot add code will be a bit messy instead.
Thanks.
-- Yasunori Goto
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