3.7-rc6 memory accounting problem (manifests like a memory leak)

[Dave Hansen <dave@linux.vnet.ibm.com>]

page_owner didn't help, at least not directly.  As the pages "leak",
they stop showing up in page_owner, which means they're in the
allocator.  Check out buddyinfo/meminfo:

> dave@nimitz:~/ltc/linux.git$ cat /proc/buddyinfo /proc/meminfo 
> Node 0, zone      DMA      0      0      0      1      2      1      1      0      1      1      3 
> Node 0, zone    DMA32  25450  13645  11665   2994   1242    665    234     50     12      1      1 
> Node 0, zone   Normal   6494  28630  16790   5872   3524   1666    844    238    146     60    398 
> MemTotal:        7825604 kB
> MemFree:         1285260 kB
...

Just the 398 order-10 zone Normal pages account for ~1.6GB of free
memory, yet the MemFree is ~1.3GB, and that's a *SINGLE* bucket in the
buddy allocator.  Adding them all up, it's fairly close to the amount of
memory that I'm missing at the moment.

Rather than being a real leak, it looks like this might just be an
accounting problem:

$ cat /proc/zoneinfo  | egrep 'free_pages|Node'
Node 0, zone      DMA
    nr_free_pages 3976
Node 0, zone    DMA32
    nr_free_pages 177041
Node 0, zone   Normal
    nr_free_pages 16148

That 16148 pages for ZONE_NORMAL is obviously bogus compared to what
buddyinfo is saying.

Commit d1ce749a0d did mess with NR_FREE_PAGES accounting quite a bit.
Guess I'll try a revert and see where I end up.

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