THP support for PPC64

Hi,

This patchset adds transparent huge page support for PPC64.

I am marking the series to linux-mm because the PPC64 implementation
required few interface changes to core THP code. I still have considerable
number of FIXME!! in the patchset mostly related to PPC64 mm susbsytem.
Those would require closer review and once we are clear on those changes,
I will drop those FIXME!! with necessary comments.

Some numbers:

The latency measurements code from Anton  found at
http://ozlabs.org/~anton/junkcode/latency2001.c

THP disabled 64K page size
------------------------
[root@llmp24l02 ~]# ./latency2001 8G
 8589934592    731.73 cycles    205.77 ns
[root@llmp24l02 ~]# ./latency2001 8G
 8589934592    743.39 cycles    209.05 ns
[root@llmp24l02 ~]#

THP disabled large page via hugetlbfs
-------------------------------------
[root@llmp24l02 ~]# ./latency2001  -l 8G
 8589934592    416.09 cycles    117.01 ns
[root@llmp24l02 ~]# ./latency2001  -l 8G
 8589934592    415.74 cycles    116.91 ns

THP enabled 64K page size.
----------------
[root@llmp24l02 ~]# ./latency2001 8G
 8589934592    405.07 cycles    113.91 ns
[root@llmp24l02 ~]# ./latency2001 8G
 8589934592    411.82 cycles    115.81 ns
[root@llmp24l02 ~]#


We are close to hugetlbfs in latency and we can achieve this with zero
config/page reservation. Most of the allocations above are fault allocated.
I haven't really measured the collapse alloc impact.

Another test that does 50000000 random access over 1GB area goes from
2.65 seconds to 1.07 seconds with this patchset.

Changes from RFC V1:
* HugeTLB fs now works
* Compile issues fixed
* rebased to v3.8
* Patch series reorded so that ppc64 cleanups and MM THP changes are moved
  early in the series. This should help in picking those patches early.

Thanks,
-aneesh

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