Re: [PATCh v3] powerpc: add hugepagesz boot-time parameter

Arnd Bergmann wrote:

We started discussing this in v1, but the discussion got sidetracked:
Is there a technical reason why you don't also allow 1M pages, which
may be useful in certain scenarios?
  

No, it was mostly a matter of the time I have had and machines easily
available to me for testing.  I don't know of a technical reason that
would prevent supporting 1M huge pages, but would want the tests in the
libhugetlbfs suite to pass, etc.

On the Cell/B.E. platforms (IBM/Mercury blades, Toshiba Celleb, PS3), the
second large page size is an option that can be set in a HID SPR
to either 64KB or 1MB. Unfortunately, we can't do these two simultaneously,
but the firmware can change the default and put it into the device tree,
or you could have the kernel override the firmware settings.

Going a lot further, do you have plans for a fully dynamic hugepage size,
e.g. using a mount option for hugetlbfs? I can see that as rather useful,
but at the same time it's probably much more complicated than the boot time
option.
  

Eventually we will want to support dynamic huge page sizes.  This is
already being looked into.  In the meantime we can have some flexibility
with a boot-time parameter though.

	Arnd <><
  

Jon