the trouble with large pages

[Hollis Blanchard <hollisb-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

The PowerPC 440 Linux kernel uses 256MB pages for the linear mapping.
When we run that as a guest, those pages would of course need to be
physically contiguous in the host.

I think long-term the KVM plan is to move memory allocation out of the
kernel (where it currently uses vmalloc) into userspace, with the idea
being that userspace could allocate memory via hugetlbfs. Anybody tried
hugetlbfs on 440 or e500?

A poor-man's equivalent might be to limit the host memory to e.g. 256MB,
then have userspace mmap(/dev/ram) starting there.

Another possibility is to fake out guest large pages by actually using
small pages on the host, and handle the extra faults in KVM without
notifying the guest.

-- 
Hollis Blanchard
IBM Linux Technology Center


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