Re: [PATCH/RFC] Shared page tables

[Robin Holt <holt@sgi.com>]

Dave,

This appears to work on ia64 with the attached patch.  Could you
send me any test application you think would be helpful for me
to verify it is operating correctly?  I could not get the PTSHARE_PUD
to compile.  I put _NO_ effort into it.  I found the following line
was invalid and quit trying.

> +	spged = pgd_val(0);

Thanks,
Robin Holt


Index: linux-2.6/arch/ia64/Kconfig
===================================================================
--- linux-2.6.orig/arch/ia64/Kconfig	2006-01-14 07:16:46.149226872 -0600
+++ linux-2.6/arch/ia64/Kconfig	2006-01-14 07:25:02.228853432 -0600
@@ -289,6 +289,38 @@ source "mm/Kconfig"
 config ARCH_SELECT_MEMORY_MODEL
 	def_bool y
 
+config PTSHARE
+	bool "Share page tables"
+	default y
+	help
+	  Turn on sharing of page tables between processes for large shared
+	  memory regions.
+
+menu "Page table levels to share"
+	depends on PTSHARE
+
+config PTSHARE_PTE
+	bool "Bottom level table (PTE)"
+	depends on PTSHARE
+	default y
+
+config PTSHARE_PMD
+	bool "Middle level table (PMD)"
+	depends on PTSHARE
+	default y
+
+config PTSHARE_PUD
+	bool "Upper level table (PUD)"
+	depends on PTSHARE && PGTABLE_4
+	default n
+
+endmenu
+
+config PTSHARE_HUGEPAGE
+	bool
+	depends on PTSHARE && PTSHARE_PMD
+	default y
+
 config ARCH_DISCONTIGMEM_ENABLE
 	def_bool y
 	help
Index: linux-2.6/include/asm-ia64/pgtable.h
===================================================================
--- linux-2.6.orig/include/asm-ia64/pgtable.h	2006-01-14 09:49:47.628417563 -0600
+++ linux-2.6/include/asm-ia64/pgtable.h	2006-01-14 09:51:25.315194368 -0600
@@ -283,14 +283,16 @@ ia64_phys_addr_valid (unsigned long addr
 #define pud_bad(pud)			(!ia64_phys_addr_valid(pud_val(pud)))
 #define pud_present(pud)		(pud_val(pud) != 0UL)
 #define pud_clear(pudp)			(pud_val(*(pudp)) = 0UL)
-#define pud_page(pud)			((unsigned long) __va(pud_val(pud) & _PFN_MASK))
+#define pud_page_kernel(pud)		((unsigned long) __va(pud_val(pud) & _PFN_MASK))
+#define pud_page(pud)			virt_to_page((pud_val(pud) + PAGE_OFFSET))
 
 #ifdef CONFIG_PGTABLE_4
 #define pgd_none(pgd)			(!pgd_val(pgd))
 #define pgd_bad(pgd)			(!ia64_phys_addr_valid(pgd_val(pgd)))
 #define pgd_present(pgd)		(pgd_val(pgd) != 0UL)
 #define pgd_clear(pgdp)			(pgd_val(*(pgdp)) = 0UL)
-#define pgd_page(pgd)			((unsigned long) __va(pgd_val(pgd) & _PFN_MASK))
+#define pgd_page_kernel(pgd)		((unsigned long) __va(pgd_val(pgd) & _PFN_MASK))
+#define pgd_page(pgd)			virt_to_page((pgd_val(pgd) + PAGE_OFFSET))
 #endif
 
 /*
@@ -363,12 +365,12 @@ pgd_offset (struct mm_struct *mm, unsign
 #ifdef CONFIG_PGTABLE_4
 /* Find an entry in the second-level page table.. */
 #define pud_offset(dir,addr) \
-	((pud_t *) pgd_page(*(dir)) + (((addr) >> PUD_SHIFT) & (PTRS_PER_PUD - 1)))
+	((pud_t *) pgd_page_kernel(*(dir)) + (((addr) >> PUD_SHIFT) & (PTRS_PER_PUD - 1)))
 #endif
 
 /* Find an entry in the third-level page table.. */
 #define pmd_offset(dir,addr) \
-	((pmd_t *) pud_page(*(dir)) + (((addr) >> PMD_SHIFT) & (PTRS_PER_PMD - 1)))
+	((pmd_t *) pud_page_kernel(*(dir)) + (((addr) >> PMD_SHIFT) & (PTRS_PER_PMD - 1)))
 
 /*
  * Find an entry in the third-level page table.  This looks more complicated than it
-
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