[PATCH 1/1] Page Table cleanup patch

[PATCH 1/1] Page Table cleanup patch

[Paul Davies]

This patch is a proposed cleanup of the current page table organisation.
Such a cleanup would be a logical first step towards introducing at least
a partial clean page table interface, geared towards providing enhanced 
virtualization oportunities for x86.  It is also a common sense cleanup 
in its own right.

 * Creates mlpt.c to hold the page table implementation currently held 
   in memory.c.
 * Adjust Makefile 
 * Move implementation dependent page table code out of 
   include/linux/mm.h into include/linux/mlpt-mm.h
 * Move implementation dependent page table code out of 
   include/asm-generic/pgtable.h to include/asm-generic/pgtable-mlpt.h

mlpt stands from multi level page table.

Signed-Off-By: Paul Davies <pauld@gelato.unsw.edu.au>

---

 include/asm-generic/pgtable-mlpt.h |   79 ++++++++++++++++++++
 include/asm-generic/pgtable.h      |   68 -----------------
 include/linux/mlpt-mm.h            |   75 +++++++++++++++++++
 include/linux/mm.h                 |   71 ------------------
 mm/Makefile                        |    2 
 mm/memory.c                        |  121 -------------------------------
 mm/mlpt.c                          |  141 +++++++++++++++++++++++++++++++++++++
 7 files changed, 299 insertions(+), 258 deletions(-)
Index: linux-2.6.20-rc5/mm/Makefile
===================================================================
--- linux-2.6.20-rc5.orig/mm/Makefile	2007-01-24 11:46:30.441362000 +1100
+++ linux-2.6.20-rc5/mm/Makefile	2007-01-24 11:46:32.141362000 +1100
@@ -5,7 +5,7 @@
 mmu-y			:= nommu.o
 mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
 			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
-			   vmalloc.o
+			   vmalloc.o mlpt.o
 
 obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   page_alloc.o page-writeback.o pdflush.o \
Index: linux-2.6.20-rc5/mm/memory.c
===================================================================
--- linux-2.6.20-rc5.orig/mm/memory.c	2007-01-24 11:46:30.441362000 +1100
+++ linux-2.6.20-rc5/mm/memory.c	2007-01-24 11:46:32.145362000 +1100
@@ -93,31 +93,6 @@
 }
 __setup("norandmaps", disable_randmaps);
 
-
-/*
- * If a p?d_bad entry is found while walking page tables, report
- * the error, before resetting entry to p?d_none.  Usually (but
- * very seldom) called out from the p?d_none_or_clear_bad macros.
- */
-
-void pgd_clear_bad(pgd_t *pgd)
-{
-	pgd_ERROR(*pgd);
-	pgd_clear(pgd);
-}
-
-void pud_clear_bad(pud_t *pud)
-{
-	pud_ERROR(*pud);
-	pud_clear(pud);
-}
-
-void pmd_clear_bad(pmd_t *pmd)
-{
-	pmd_ERROR(*pmd);
-	pmd_clear(pmd);
-}
-
 /*
  * Note: this doesn't free the actual pages themselves. That
  * has been handled earlier when unmapping all the memory regions.
@@ -300,41 +275,6 @@
 	}
 }
 
-int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
-{
-	struct page *new = pte_alloc_one(mm, address);
-	if (!new)
-		return -ENOMEM;
-
-	pte_lock_init(new);
-	spin_lock(&mm->page_table_lock);
-	if (pmd_present(*pmd)) {	/* Another has populated it */
-		pte_lock_deinit(new);
-		pte_free(new);
-	} else {
-		mm->nr_ptes++;
-		inc_zone_page_state(new, NR_PAGETABLE);
-		pmd_populate(mm, pmd, new);
-	}
-	spin_unlock(&mm->page_table_lock);
-	return 0;
-}
-
-int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
-{
-	pte_t *new = pte_alloc_one_kernel(&init_mm, address);
-	if (!new)
-		return -ENOMEM;
-
-	spin_lock(&init_mm.page_table_lock);
-	if (pmd_present(*pmd))		/* Another has populated it */
-		pte_free_kernel(new);
-	else
-		pmd_populate_kernel(&init_mm, pmd, new);
-	spin_unlock(&init_mm.page_table_lock);
-	return 0;
-}
-
 static inline void add_mm_rss(struct mm_struct *mm, int file_rss, int anon_rss)
 {
 	if (file_rss)
@@ -2476,67 +2416,6 @@
 
 EXPORT_SYMBOL_GPL(__handle_mm_fault);
 
-#ifndef __PAGETABLE_PUD_FOLDED
-/*
- * Allocate page upper directory.
- * We've already handled the fast-path in-line.
- */
-int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
-{
-	pud_t *new = pud_alloc_one(mm, address);
-	if (!new)
-		return -ENOMEM;
-
-	spin_lock(&mm->page_table_lock);
-	if (pgd_present(*pgd))		/* Another has populated it */
-		pud_free(new);
-	else
-		pgd_populate(mm, pgd, new);
-	spin_unlock(&mm->page_table_lock);
-	return 0;
-}
-#else
-/* Workaround for gcc 2.96 */
-int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
-{
-	return 0;
-}
-#endif /* __PAGETABLE_PUD_FOLDED */
-
-#ifndef __PAGETABLE_PMD_FOLDED
-/*
- * Allocate page middle directory.
- * We've already handled the fast-path in-line.
- */
-int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
-{
-	pmd_t *new = pmd_alloc_one(mm, address);
-	if (!new)
-		return -ENOMEM;
-
-	spin_lock(&mm->page_table_lock);
-#ifndef __ARCH_HAS_4LEVEL_HACK
-	if (pud_present(*pud))		/* Another has populated it */
-		pmd_free(new);
-	else
-		pud_populate(mm, pud, new);
-#else
-	if (pgd_present(*pud))		/* Another has populated it */
-		pmd_free(new);
-	else
-		pgd_populate(mm, pud, new);
-#endif /* __ARCH_HAS_4LEVEL_HACK */
-	spin_unlock(&mm->page_table_lock);
-	return 0;
-}
-#else
-/* Workaround for gcc 2.96 */
-int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
-{
-	return 0;
-}
-#endif /* __PAGETABLE_PMD_FOLDED */
-
 int make_pages_present(unsigned long addr, unsigned long end)
 {
 	int ret, len, write;
Index: linux-2.6.20-rc5/include/asm-generic/pgtable.h
===================================================================
--- linux-2.6.20-rc5.orig/include/asm-generic/pgtable.h	2007-01-24 11:46:30.441362000 +1100
+++ linux-2.6.20-rc5/include/asm-generic/pgtable.h	2007-01-24 11:52:28.633362000 +1100
@@ -182,72 +182,8 @@
 #define arch_leave_lazy_mmu_mode()	do {} while (0)
 #endif
 
-/*
- * When walking page tables, get the address of the next boundary,
- * or the end address of the range if that comes earlier.  Although no
- * vma end wraps to 0, rounded up __boundary may wrap to 0 throughout.
- */
-
-#define pgd_addr_end(addr, end)						\
-({	unsigned long __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK;	\
-	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
-})
-
-#ifndef pud_addr_end
-#define pud_addr_end(addr, end)						\
-({	unsigned long __boundary = ((addr) + PUD_SIZE) & PUD_MASK;	\
-	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
-})
-#endif
-
-#ifndef pmd_addr_end
-#define pmd_addr_end(addr, end)						\
-({	unsigned long __boundary = ((addr) + PMD_SIZE) & PMD_MASK;	\
-	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
-})
-#endif
-
-/*
- * When walking page tables, we usually want to skip any p?d_none entries;
- * and any p?d_bad entries - reporting the error before resetting to none.
- * Do the tests inline, but report and clear the bad entry in mm/memory.c.
- */
-void pgd_clear_bad(pgd_t *);
-void pud_clear_bad(pud_t *);
-void pmd_clear_bad(pmd_t *);
-
-static inline int pgd_none_or_clear_bad(pgd_t *pgd)
-{
-	if (pgd_none(*pgd))
-		return 1;
-	if (unlikely(pgd_bad(*pgd))) {
-		pgd_clear_bad(pgd);
-		return 1;
-	}
-	return 0;
-}
-
-static inline int pud_none_or_clear_bad(pud_t *pud)
-{
-	if (pud_none(*pud))
-		return 1;
-	if (unlikely(pud_bad(*pud))) {
-		pud_clear_bad(pud);
-		return 1;
-	}
-	return 0;
-}
-
-static inline int pmd_none_or_clear_bad(pmd_t *pmd)
-{
-	if (pmd_none(*pmd))
-		return 1;
-	if (unlikely(pmd_bad(*pmd))) {
-		pmd_clear_bad(pmd);
-		return 1;
-	}
-	return 0;
-}
 #endif /* !__ASSEMBLY__ */
 
+#include <asm-generic/pgtable-mlpt.h>
+
 #endif /* _ASM_GENERIC_PGTABLE_H */
Index: linux-2.6.20-rc5/include/linux/mlpt-mm.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.20-rc5/include/linux/mlpt-mm.h	2007-01-24 11:46:32.169362000 +1100
@@ -0,0 +1,75 @@
+#ifndef _LINUX_MLPT_MM_H
+#define _LINUX_MLPT_MM_H
+
+int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address);
+int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address);
+int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address);
+int __pte_alloc_kernel(pmd_t *pmd, unsigned long address);
+
+/*
+ * The following ifdef needed to get the 4level-fixup.h header to work.
+ * Remove it when 4level-fixup.h has been removed.
+ */
+#if defined(CONFIG_MMU) && !defined(__ARCH_HAS_4LEVEL_HACK)
+static inline pud_t *pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
+{
+	return (unlikely(pgd_none(*pgd)) && __pud_alloc(mm, pgd, address))?
+		NULL: pud_offset(pgd, address);
+}
+
+static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
+{
+	return (unlikely(pud_none(*pud)) && __pmd_alloc(mm, pud, address))?
+		NULL: pmd_offset(pud, address);
+}
+#endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */
+
+#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
+/*
+ * We tuck a spinlock to guard each pagetable page into its struct page,
+ * at page->private, with BUILD_BUG_ON to make sure that this will not
+ * overflow into the next struct page (as it might with DEBUG_SPINLOCK).
+ * When freeing, reset page->mapping so free_pages_check won't complain.
+ */
+#define __pte_lockptr(page)	&((page)->ptl)
+#define pte_lock_init(_page)	do {					\
+	spin_lock_init(__pte_lockptr(_page));				\
+} while (0)
+#define pte_lock_deinit(page)	((page)->mapping = NULL)
+#define pte_lockptr(mm, pmd)	({(void)(mm); __pte_lockptr(pmd_page(*(pmd)));})
+#else
+/*
+ * We use mm->page_table_lock to guard all pagetable pages of the mm.
+ */
+#define pte_lock_init(page)	do {} while (0)
+#define pte_lock_deinit(page)	do {} while (0)
+#define pte_lockptr(mm, pmd)	({(void)(pmd); &(mm)->page_table_lock;})
+#endif /* NR_CPUS < CONFIG_SPLIT_PTLOCK_CPUS */
+
+#define pte_offset_map_lock(mm, pmd, address, ptlp)	\
+({							\
+	spinlock_t *__ptl = pte_lockptr(mm, pmd);	\
+	pte_t *__pte = pte_offset_map(pmd, address);	\
+	*(ptlp) = __ptl;				\
+	spin_lock(__ptl);				\
+	__pte;						\
+})
+
+#define pte_unmap_unlock(pte, ptl)	do {		\
+	spin_unlock(ptl);				\
+	pte_unmap(pte);					\
+} while (0)
+
+#define pte_alloc_map(mm, pmd, address)			\
+	((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
+		NULL: pte_offset_map(pmd, address))
+
+#define pte_alloc_map_lock(mm, pmd, address, ptlp)	\
+	((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
+		NULL: pte_offset_map_lock(mm, pmd, address, ptlp))
+
+#define pte_alloc_kernel(pmd, address)			\
+	((unlikely(!pmd_present(*(pmd))) && __pte_alloc_kernel(pmd, address))? \
+		NULL: pte_offset_kernel(pmd, address))
+
+#endif
Index: linux-2.6.20-rc5/include/linux/mm.h
===================================================================
--- linux-2.6.20-rc5.orig/include/linux/mm.h	2007-01-24 11:46:30.441362000 +1100
+++ linux-2.6.20-rc5/include/linux/mm.h	2007-01-24 11:46:32.169362000 +1100
@@ -853,76 +853,7 @@
 
 extern pte_t *FASTCALL(get_locked_pte(struct mm_struct *mm, unsigned long addr, spinlock_t **ptl));
 
-int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address);
-int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address);
-int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address);
-int __pte_alloc_kernel(pmd_t *pmd, unsigned long address);
-
-/*
- * The following ifdef needed to get the 4level-fixup.h header to work.
- * Remove it when 4level-fixup.h has been removed.
- */
-#if defined(CONFIG_MMU) && !defined(__ARCH_HAS_4LEVEL_HACK)
-static inline pud_t *pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
-{
-	return (unlikely(pgd_none(*pgd)) && __pud_alloc(mm, pgd, address))?
-		NULL: pud_offset(pgd, address);
-}
-
-static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
-{
-	return (unlikely(pud_none(*pud)) && __pmd_alloc(mm, pud, address))?
-		NULL: pmd_offset(pud, address);
-}
-#endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */
-
-#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
-/*
- * We tuck a spinlock to guard each pagetable page into its struct page,
- * at page->private, with BUILD_BUG_ON to make sure that this will not
- * overflow into the next struct page (as it might with DEBUG_SPINLOCK).
- * When freeing, reset page->mapping so free_pages_check won't complain.
- */
-#define __pte_lockptr(page)	&((page)->ptl)
-#define pte_lock_init(_page)	do {					\
-	spin_lock_init(__pte_lockptr(_page));				\
-} while (0)
-#define pte_lock_deinit(page)	((page)->mapping = NULL)
-#define pte_lockptr(mm, pmd)	({(void)(mm); __pte_lockptr(pmd_page(*(pmd)));})
-#else
-/*
- * We use mm->page_table_lock to guard all pagetable pages of the mm.
- */
-#define pte_lock_init(page)	do {} while (0)
-#define pte_lock_deinit(page)	do {} while (0)
-#define pte_lockptr(mm, pmd)	({(void)(pmd); &(mm)->page_table_lock;})
-#endif /* NR_CPUS < CONFIG_SPLIT_PTLOCK_CPUS */
-
-#define pte_offset_map_lock(mm, pmd, address, ptlp)	\
-({							\
-	spinlock_t *__ptl = pte_lockptr(mm, pmd);	\
-	pte_t *__pte = pte_offset_map(pmd, address);	\
-	*(ptlp) = __ptl;				\
-	spin_lock(__ptl);				\
-	__pte;						\
-})
-
-#define pte_unmap_unlock(pte, ptl)	do {		\
-	spin_unlock(ptl);				\
-	pte_unmap(pte);					\
-} while (0)
-
-#define pte_alloc_map(mm, pmd, address)			\
-	((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
-		NULL: pte_offset_map(pmd, address))
-
-#define pte_alloc_map_lock(mm, pmd, address, ptlp)	\
-	((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
-		NULL: pte_offset_map_lock(mm, pmd, address, ptlp))
-
-#define pte_alloc_kernel(pmd, address)			\
-	((unlikely(!pmd_present(*(pmd))) && __pte_alloc_kernel(pmd, address))? \
-		NULL: pte_offset_kernel(pmd, address))
+#include <linux/mlpt-mm.h>
 
 extern void free_area_init(unsigned long * zones_size);
 extern void free_area_init_node(int nid, pg_data_t *pgdat,
Index: linux-2.6.20-rc5/mm/mlpt.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.20-rc5/mm/mlpt.c	2007-01-24 11:46:32.169362000 +1100
@@ -0,0 +1,141 @@
+#include <linux/kernel_stat.h>
+#include <linux/mm.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/swap.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/module.h>
+#include <linux/delayacct.h>
+#include <linux/init.h>
+#include <linux/writeback.h>
+
+#include <asm/pgalloc.h>
+#include <asm/uaccess.h>
+#include <asm/tlb.h>
+#include <asm/tlbflush.h>
+#include <asm/pgtable.h>
+
+#include <linux/swapops.h>
+#include <linux/elf.h>
+
+/*
+ * If a p?d_bad entry is found while walking page tables, report
+ * the error, before resetting entry to p?d_none.  Usually (but
+ * very seldom) called out from the p?d_none_or_clear_bad macros.
+ */
+
+void pgd_clear_bad(pgd_t *pgd)
+{
+	pgd_ERROR(*pgd);
+	pgd_clear(pgd);
+}
+
+void pud_clear_bad(pud_t *pud)
+{
+	pud_ERROR(*pud);
+	pud_clear(pud);
+}
+
+void pmd_clear_bad(pmd_t *pmd)
+{
+	pmd_ERROR(*pmd);
+	pmd_clear(pmd);
+}
+
+int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
+{
+	struct page *new = pte_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	pte_lock_init(new);
+	spin_lock(&mm->page_table_lock);
+	if (pmd_present(*pmd)) {	/* Another has populated it */
+		pte_lock_deinit(new);
+		pte_free(new);
+	} else {
+		mm->nr_ptes++;
+		inc_zone_page_state(new, NR_PAGETABLE);
+		pmd_populate(mm, pmd, new);
+	}
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+
+int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
+{
+	pte_t *new = pte_alloc_one_kernel(&init_mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&init_mm.page_table_lock);
+	if (pmd_present(*pmd))		/* Another has populated it */
+		pte_free_kernel(new);
+	else
+		pmd_populate_kernel(&init_mm, pmd, new);
+	spin_unlock(&init_mm.page_table_lock);
+	return 0;
+}
+
+#ifndef __PAGETABLE_PUD_FOLDED
+/*
+ * Allocate page upper directory.
+ * We've already handled the fast-path in-line.
+ */
+int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
+{
+	pud_t *new = pud_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&mm->page_table_lock);
+	if (pgd_present(*pgd))		/* Another has populated it */
+		pud_free(new);
+	else
+		pgd_populate(mm, pgd, new);
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+#else
+/* Workaround for gcc 2.96 */
+int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
+{
+	return 0;
+}
+#endif /* __PAGETABLE_PUD_FOLDED */
+
+#ifndef __PAGETABLE_PMD_FOLDED
+/*
+ * Allocate page middle directory.
+ * We've already handled the fast-path in-line.
+ */
+int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
+{
+	pmd_t *new = pmd_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	spin_lock(&mm->page_table_lock);
+#ifndef __ARCH_HAS_4LEVEL_HACK
+	if (pud_present(*pud))		/* Another has populated it */
+		pmd_free(new);
+	else
+		pud_populate(mm, pud, new);
+#else
+	if (pgd_present(*pud))		/* Another has populated it */
+		pmd_free(new);
+	else
+		pgd_populate(mm, pud, new);
+#endif /* __ARCH_HAS_4LEVEL_HACK */
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+#else
+/* Workaround for gcc 2.96 */
+int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
+{
+	return 0;
+}
+#endif /* __PAGETABLE_PMD_FOLDED */
Index: linux-2.6.20-rc5/include/asm-generic/pgtable-mlpt.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.20-rc5/include/asm-generic/pgtable-mlpt.h	2007-01-24 11:52:12.141362000 +1100
@@ -0,0 +1,79 @@
+#ifndef _ASM_GENERIC_PGTABLE_MLPT_H
+#define _ASM_GENERIC_PGTABLE_MLPT_H
+
+#ifndef __ASSEMBLY__
+
+#ifndef __HAVE_ARCH_PGD_OFFSET_GATE
+#define pgd_offset_gate(mm, addr)	pgd_offset(mm, addr)
+#endif
+
+/*
+ * When walking page tables, get the address of the next boundary,
+ * or the end address of the range if that comes earlier.  Although no
+ * vma end wraps to 0, rounded up __boundary may wrap to 0 throughout.
+ */
+
+#define pgd_addr_end(addr, end)						\
+({	unsigned long __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK;	\
+	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
+})
+
+#ifndef pud_addr_end
+#define pud_addr_end(addr, end)						\
+({	unsigned long __boundary = ((addr) + PUD_SIZE) & PUD_MASK;	\
+	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
+})
+#endif
+
+#ifndef pmd_addr_end
+#define pmd_addr_end(addr, end)						\
+({	unsigned long __boundary = ((addr) + PMD_SIZE) & PMD_MASK;	\
+	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
+})
+#endif
+
+/*
+ * When walking page tables, we usually want to skip any p?d_none entries;
+ * and any p?d_bad entries - reporting the error before resetting to none.
+ * Do the tests inline, but report and clear the bad entry in mm/memory.c.
+ */
+void pgd_clear_bad(pgd_t *);
+void pud_clear_bad(pud_t *);
+void pmd_clear_bad(pmd_t *);
+
+static inline int pgd_none_or_clear_bad(pgd_t *pgd)
+{
+	if (pgd_none(*pgd))
+		return 1;
+	if (unlikely(pgd_bad(*pgd))) {
+		pgd_clear_bad(pgd);
+		return 1;
+	}
+	return 0;
+}
+
+static inline int pud_none_or_clear_bad(pud_t *pud)
+{
+	if (pud_none(*pud))
+		return 1;
+	if (unlikely(pud_bad(*pud))) {
+		pud_clear_bad(pud);
+		return 1;
+	}
+	return 0;
+}
+
+static inline int pmd_none_or_clear_bad(pmd_t *pmd)
+{
+	if (pmd_none(*pmd))
+		return 1;
+	if (unlikely(pmd_bad(*pmd))) {
+		pmd_clear_bad(pmd);
+		return 1;
+	}
+	return 0;
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* _ASM_GENERIC_PGTABLE_H */

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Re: [PATCH 1/1] Page Table cleanup patch

[Nick Piggin]

Paul Davies wrote:
> This patch is a proposed cleanup of the current page table organisation.
> Such a cleanup would be a logical first step towards introducing at least
> a partial clean page table interface, geared towards providing enhanced 
> virtualization oportunities for x86.  It is also a common sense cleanup 
> in its own right.
> 
>  * Creates mlpt.c to hold the page table implementation currently held 
>    in memory.c.
>  * Adjust Makefile 
>  * Move implementation dependent page table code out of 
>    include/linux/mm.h into include/linux/mlpt-mm.h
>  * Move implementation dependent page table code out of 
>    include/asm-generic/pgtable.h to include/asm-generic/pgtable-mlpt.h
> 
> mlpt stands from multi level page table.

Hi Paul,

I'm not sure that I see the point of this patch alone, as there is still
all the mlpt implementation details in all the page table walkers. Or
did you have a scheme to change implementations somehow just using the
p*d_addr_next?

> -#ifndef __PAGETABLE_PUD_FOLDED
> -/*
> - * Allocate page upper directory.
> - * We've already handled the fast-path in-line.
> - */
> -int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
> -{
> -	pud_t *new = pud_alloc_one(mm, address);
> -	if (!new)
> -		return -ENOMEM;
> -
> -	spin_lock(&mm->page_table_lock);
> -	if (pgd_present(*pgd))		/* Another has populated it */
> -		pud_free(new);
> -	else
> -		pgd_populate(mm, pgd, new);
> -	spin_unlock(&mm->page_table_lock);
> -	return 0;
> -}
> -#else
> -/* Workaround for gcc 2.96 */
> -int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
> -{
> -	return 0;
> -}
> -#endif /* __PAGETABLE_PUD_FOLDED */

...

> -/* Workaround for gcc 2.96 */
> -int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
> -{
> -	return 0;
> -}
> -#endif /* __PAGETABLE_PMD_FOLDED */

Hmm, we're gcc-3.2 minimum now -- let's get rid of that crud?

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Re: [PATCH 1/1] Page Table cleanup patch

[Paul Cameron Davies]

Hi Nick

On Wed, 24 Jan 2007, Nick Piggin wrote:

> Paul Davies wrote:
>> This patch is a proposed cleanup of the current page table organisation.
>> Such a cleanup would be a logical first step towards introducing at least
>> a partial clean page table interface, geared towards providing enhanced 
>> virtualization oportunities for x86.  It is also a common sense cleanup in 
>> its own right.
>>
>>  * Creates mlpt.c to hold the page table implementation currently held 
>> in memory.c.
>>  * Adjust Makefile  * Move implementation dependent page table code out of 
>> include/linux/mm.h into include/linux/mlpt-mm.h
>>  * Move implementation dependent page table code out of 
>> include/asm-generic/pgtable.h to include/asm-generic/pgtable-mlpt.h
>> 
>> mlpt stands from multi level page table.
>
> Hi Paul,
>
> I'm not sure that I see the point of this patch alone, as there is still
> all the mlpt implementation details in all the page table walkers. Or
> did you have a scheme to change implementations somehow just using the
> p*d_addr_next?

This patch alone doesn't acheive nearly enough.  Separating out as much
implementation (without tackling the walkers) would be a start though.
The MLPT appears to be intrinsic to the kernel owing to its open coding, 
and starting to isolate its implementation (even partially) is an 
important step towards destroying this misconception.

I strongly prefer not to go down the path of using a scheme to change 
implementations with p*d_addr_next.  I tried this kind of thing early on 
and it was horribly ugly.  There are far cleaner ways to do it.

Cheers

Paul Davies

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