[PATCH] Calculate exactly how many pointers in PGD

[PATCH] Calculate exactly how many pointers in PGD

[Songmao Tian]

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.

Signed-off-by: Songmao Tian <tiansm@lemote.com>
---
 include/asm-mips/pgtable-32.h |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/include/asm-mips/pgtable-32.h b/include/asm-mips/pgtable-32.h
index 59c865d..dc8ec21 100644
--- a/include/asm-mips/pgtable-32.h
+++ b/include/asm-mips/pgtable-32.h
@@ -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)