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

[Jon Tollefson <kniht@linux.vnet.ibm.com>]

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