Messages in this thread | | | Date | Mon, 16 Feb 2009 09:28:22 -0800 | From | "H. Peter Anvin" <> | Subject | Re: #tj-percpu has been rebased |
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Rusty Russell wrote: > > But note that for the non-NUMA case, you can just use kmalloc/__get_free_pages > and no remapping tricks are necessary at all. >
Only if your chunks are really small. Keep in mind that num_possible_cpus() may be 4096, and so it is unlikely you'll be able to get enough contiguous pages unless you're using the largepage pool, and even then you only get 512 bytes per cpu.
All in all I think a dedicated virtual zone per CPU as opposed to interleaving them seems to make more sense. Even with 4096 CPUs and reserving, say, 256 MB per CPU it's not that much address space in the context of a 47-bit kernel space. On 32 bits I don't think anything but the most trivial amount of percpu space is going to fly no matter what.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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