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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 <>

    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

    - 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;
    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 @@

    #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);

    -#define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) \
    - free_pgd_range(tlb, addr, end, floor, ceiling)
    * 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

    #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 free_pgd_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 | minimalist, thank you. NOT _the_ _other_
    | _way_ _around_!
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      Last update: 2006-03-02 05:55    [W:0.031 / U:0.072 seconds]
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