sparc64: Fix accounting issues used to size TSBs

sparc64: Fix accounting issues used to size TSBs

Orabug: 24478985

As pages are allocated by a task, counters in the mm and mm_context
structures are used to track these allocations.  These counters are
then used to size the task's TSBs.  This patch addresses issues where
counts are not maintained properly, and TSBs of the incorrect size
are created for the task.

- hugetlb pages are not included in a task's RSS calculations.  However,
  the routine do_sparc64_fault() calculates the size of base TSB block
  by subtracting total size of hugetlb pages from RSS.  Since hugetlb
  size is likely larger than RSS, a negative value is passed as an
  unsigned value to the routine which allocates the TSB block.  The
  'negative unsigned' value appears as a really big value and results in
  a maximum sized base TSB being allocated.  This is the case for almost
  all tasks using hugetlb pages.

  THP pages are also counted in huge_pte_count[MM_PTES_HUGE].  And
  unlike hugetlb pages, THP pages are included in a task's RSS.
  Therefore, both hugetlb and THP can not be counted for in
  huge_pte_count[MM_PTES_HUGE].

  Add a new counter thp_pte_count for THP pages, and use this value for
  adjusting RSS to size the base TSB.

- In order to save memory, THP makes use of a huge zero page.  This huge
  zero page does not count against a task's RSS, but it does consume TSB
  entries.  Therefore, count huge zero page entries in
  huge_pte_count[MM_PTES_HUGE].

- Accounting of THP pages is done in the routine set_pmd_at().
  Unfortunately, this does not catch the case where a THP page is split.
  To handle this case, decrement the count in pmdp_invalidate().
  pmdp_invalidate is only called when splitting a THP.  However, 'sanity
  checks' are added in case it is ever called for other purposes.

- huge_pte_count[MM_PTES_HUGE] tracks the number of HPAGE_SIZE (8M) pages
  used by the task.  This value is used to size the TSB for HPAGE_SIZE
  pages.  However, for each HPAGE_SIZE (8M) there are two REAL_HPAGE_SIZE
  (4M) pages.  The TSB contains an entry for each REAL_HPAGE_SIZE page.
  Therefore, the number of REAL_HPAGE_SIZE pages used by the task should
  be used to size the MM_PTES_HUGE TSB.  A new compile time constant
  REAL_HPAGE_PER_HPAGE is used to multiply huge_pte_count[MM_PTES_HUGE]
  before sizing the TSB.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Vijay Kumar <vijay.ac.kumar@oracle.com>
Tested-by: Vijay Kumar <vijay.ac.kumar@oracle.com>
(cherry picked from commit 417fc85e759b6d4c4602fbdbdd5375ec5ddf2cb0)
Signed-off-by: Allen Pais <allen.pais@oracle.com>