Calculate exactly how many pointers in PGD

In 32-bit kernel, we treat BadAddr as a 32-bit address, so using a page for pgd will be a waste when page size > 4k, calculating exactly how many pointers in PGD will save memory quite a bit.

---
include/asm-mips/pgtable-32.h | 7 ++++++-

1 files changed, 6 insertions(+), 1 deletions(-)

index 59c865d..dc8ec21 100644
@@ -57,7 +57,12 @@ extern int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,

#define PMD_ORDER 1
#define PTE_ORDER 0

-#define PTRS_PER_PGD ((PAGE_SIZE << PGD_ORDER) / sizeof(pgd_t))
+/*
+ * Using a page for pgd will be a waste when page size > 4k,
+ * so we calculate exactly how many pointers in PGD under
+ * 32-bit address space configuration.
+ */
+#define PTRS_PER_PGD (1 << (32 - PGDIR_SHIFT))
#define PTRS_PER_PTE ((PAGE_SIZE << PTE_ORDER) / sizeof(pte_t))

#define USER_PTRS_PER_PGD (0x80000000UL/PGDIR_SIZE)