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Subjecthugepage: Fix hugepage logic in free_pgtables()
free_pgtables() has special logic to call hugetlb_free_pgd_range()
instead of the normal free_pgd_range() on hugepage VMAs. However, the
test it uses to do so is incorrect: it calls is_hugepage_only_range on
a hugepage sized range at the start of the vma.
is_hugepage_only_range() will return true if the given range has any
intersection with a hugepage address region, and in this case the
given region need not be hugepage aligned. So, for example, this test
can return true if called on, say, a 4k VMA immediately preceding a
(nicely aligned) hugepage VMA.

At present we get away with this because the powerpc version of
hugetlb_free_pgd_range() is just a call to free_pgd_range(). On ia64
(the only other arch with a non-trivial is_hugepage_only_range()) we
get away with it for a different reason; the hugepage area is not
contiguous with the rest of the user address space, and VMAs are not
permitted in between, so the test can't return a false positive there.

Nonetheless this should be fixed. We do that in the patch below by
replacing the is_hugepage_only_range() test with an explicit test of
the VMA using is_vm_hugetlb_page().

This in turn changes behaviour for platforms where
is_hugepage_only_range() returns false always (everything except
powerpc and ia64). We address this by ensuring that
hugetlb_free_pgd_range() is defined to be identical to
free_pgd_range() (instead of a no-op) on everything except ia64. Even
so, it will prevent some otherwise possible coalescing of calls down
to free_pgd_range(). Since this only happens for hugepage VMAs,
removing this small optimization seems unlikely to cause any trouble.

This patch causes no regressions on the libhugetlbfs testsuite - ppc64
POWER5 (8-way), ppc64 G5 (2-way) and i386 Pentium M (UP).

Signed-off-by: David Gibson <dwg@au1.ibm.com>

Index: working-2.6/mm/memory.c
===================================================================
--- working-2.6.orig/mm/memory.c 2006-02-24 11:44:36.000000000 +1100
+++ working-2.6/mm/memory.c 2006-03-02 11:14:03.000000000 +1100
@@ -277,7 +277,7 @@ void free_pgtables(struct mmu_gather **t
anon_vma_unlink(vma);
unlink_file_vma(vma);

- if (is_hugepage_only_range(vma->vm_mm, addr, HPAGE_SIZE)) {
+ if (is_vm_hugetlb_page(vma)) {
hugetlb_free_pgd_range(tlb, addr, vma->vm_end,
floor, next? next->vm_start: ceiling);
} else {
@@ -285,8 +285,7 @@ void free_pgtables(struct mmu_gather **t
* Optimization: gather nearby vmas into one call down
*/
while (next && next->vm_start <= vma->vm_end + PMD_SIZE
- && !is_hugepage_only_range(vma->vm_mm, next->vm_start,
- HPAGE_SIZE)) {
+ && !is_vm_hugetlb_page(vma)) {
vma = next;
next = vma->vm_next;
anon_vma_unlink(vma);
Index: working-2.6/include/asm-ia64/page.h
===================================================================
--- working-2.6.orig/include/asm-ia64/page.h 2006-03-02 11:12:40.000000000 +1100
+++ working-2.6/include/asm-ia64/page.h 2006-03-02 11:30:26.000000000 +1100
@@ -57,6 +57,7 @@

# define HAVE_ARCH_HUGETLB_UNMAPPED_AREA
# define ARCH_HAS_HUGEPAGE_ONLY_RANGE
+# define ARCH_HAS_HUGETLB_FREE_PGD_RANGE
#endif /* CONFIG_HUGETLB_PAGE */

#ifdef __ASSEMBLY__
Index: working-2.6/include/asm-powerpc/pgtable.h
===================================================================
--- working-2.6.orig/include/asm-powerpc/pgtable.h 2006-02-24 11:44:35.000000000 +1100
+++ working-2.6/include/asm-powerpc/pgtable.h 2006-03-02 11:29:26.000000000 +1100
@@ -468,11 +468,6 @@ extern pgd_t swapper_pg_dir[];

extern void paging_init(void);

-#ifdef CONFIG_HUGETLB_PAGE
-#define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) \
- free_pgd_range(tlb, addr, end, floor, ceiling)
-#endif
-
/*
* This gets called at the end of handling a page fault, when
* the kernel has put a new PTE into the page table for the process.
Index: working-2.6/include/linux/hugetlb.h
===================================================================
--- working-2.6.orig/include/linux/hugetlb.h 2006-03-02 11:12:40.000000000 +1100
+++ working-2.6/include/linux/hugetlb.h 2006-03-02 11:47:30.000000000 +1100
@@ -43,8 +43,10 @@ void hugetlb_change_protection(struct vm

#ifndef ARCH_HAS_HUGEPAGE_ONLY_RANGE
#define is_hugepage_only_range(mm, addr, len) 0
-#define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) \
- do { } while (0)
+#endif
+
+#ifndef ARCH_HAS_HUGETLB_FREE_PGD_RANGE
+#define hugetlb_free_pgd_range free_pgd_range
#endif

#ifndef ARCH_HAS_PREPARE_HUGEPAGE_RANGE
@@ -93,8 +95,7 @@ static inline unsigned long hugetlb_tota
#define prepare_hugepage_range(addr, len) (-EINVAL)
#define pmd_huge(x) 0
#define is_hugepage_only_range(mm, addr, len) 0
-#define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) \
- do { } while (0)
+#define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) ({BUG(); 0; })
#define hugetlb_fault(mm, vma, addr, write) ({ BUG(); 0; })

#define hugetlb_change_protection(vma, address, end, newprot)
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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