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[PATCH] Calculate exactly how many pointers in PGD

To: linux-mips <linux-mips@linux-mips.org>
Subject: [PATCH] Calculate exactly how many pointers in PGD
From: Songmao Tian <tiansm@lemote.com>
Date: Tue, 18 Sep 2007 21:33:25 +0800
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: Icedove 1.5.0.8 (X11/20061116)
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)


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