1M hugepage size being registered on Linux

[Benjamin Herrenschmidt]

On Wed, 2017-06-21 at 20:33 +1000, Michael Ellerman wrote:
> victora <victora at linux.vnet.ibm.com> writes:
> 
> > Hi Alistair/Jeremy,
> > 
> > I am working on a bug related to 1M hugepage size being registered on 
> > Linux (Power 8 Baremetal - Garrison).
> 
> Wasn't that caused by a firmware bug?
> 
> > I was checking dmesg and it seems that 1M page size is coming from 
> > firmware to Linux.
> > 
> > [    0.000000] base_shift=20: shift=20, sllp=0x0130, avpnm=0x00000000, 
> > tlbiel=0, penc=2
> > [    1.528867] HugeTLB registered 1 MB page size, pre-allocated 0 pages
> > 
> > Should Linux support this page size?
> 
> Does it work? :)
> 
> The user manual says it's a supported size, but I thought it didn't work
> (in hardware) for some reason.

Right, I thought there was some config bit to switch between 1M and 16M
and that had never been fully verified ? I don't remember the details.