Calculate exactly how many ptr is needed for pgd
RFC 1/1 Calculate exactly how many ptr is needed for pgd
Under 32-bit kernel with 4k page, a page is needed for a pgd, but when page size > 4k, a page will be too much.
include/asm-mips/pgtable-32.h +0 -0
@@ -67,7 +67,8 @@ extern int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,
#define PTE_ORDER 0
#endif
-#define PTRS_PER_PGD ((PAGE_SIZE << PGD_ORDER) / sizeof(pgd_t))
+/* Using a page for pgd will be a waste when page size > 4k */
+#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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It works well. If I start xorg+xfce, it can save 2.5MB memory in my system.
Thanks, songmao.
2007/7/31, Songmao Tian <[email protected]>:
Quoted 20 lines
Under 32-bit kernel with 4k page, a page is needed for a pgd, but when page size > 4k, a page will be too much.
include/asm-mips/pgtable-32.h +2
-1@@ -67,7 +67,8 @@ extern int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,#define PTE_ORDER 0#endif -#define PTRS_PER_PGD ((PAGE_SIZE << PGD_ORDER) / sizeof(pgd_t)) +/* Using a page for pgd will be a waste when page size > 4k */ +#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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