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    SubjectRe: [PATCH 1/7] Introduce the pagetable_operations and associated helper macros.
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    On (19/02/07 22:29), Christoph Hellwig didst pronounce:
    > On Mon, Feb 19, 2007 at 10:31:34AM -0800, Adam Litke wrote:
    > > Signed-off-by: Adam Litke <agl@us.ibm.com>
    > > ---
    > >
    > > include/linux/mm.h | 25 +++++++++++++++++++++++++
    > > 1 files changed, 25 insertions(+), 0 deletions(-)
    > >
    > > diff --git a/include/linux/mm.h b/include/linux/mm.h
    > > index 2d2c08d..a2fa66d 100644
    > > --- a/include/linux/mm.h
    > > +++ b/include/linux/mm.h
    > > @@ -98,6 +98,7 @@ struct vm_area_struct {
    > >
    > > /* Function pointers to deal with this struct. */
    > > struct vm_operations_struct * vm_ops;
    > > + struct pagetable_operations_struct * pagetable_ops;
    > >
    > > /* Information about our backing store: */
    > > unsigned long vm_pgoff; /* Offset (within vm_file) in PAGE_SIZE
    > > @@ -218,6 +219,30 @@ struct vm_operations_struct {
    > > };
    > >
    > > struct mmu_gather;
    > > +
    > > +struct pagetable_operations_struct {
    > > + int (*fault)(struct mm_struct *mm,
    > > + struct vm_area_struct *vma,
    > > + unsigned long address, int write_access);
    > > + int (*copy_vma)(struct mm_struct *dst, struct mm_struct *src,
    > > + struct vm_area_struct *vma);
    > > + int (*pin_pages)(struct mm_struct *mm, struct vm_area_struct *vma,
    > > + struct page **pages, struct vm_area_struct **vmas,
    > > + unsigned long *position, int *length, int i);
    > > + void (*change_protection)(struct vm_area_struct *vma,
    > > + unsigned long address, unsigned long end, pgprot_t newprot);
    > > + unsigned long (*unmap_page_range)(struct vm_area_struct *vma,
    > > + unsigned long address, unsigned long end, long *zap_work);
    > > + void (*free_pgtable_range)(struct mmu_gather **tlb,
    > > + unsigned long addr, unsigned long end,
    > > + unsigned long floor, unsigned long ceiling);
    > > +};
    >
    > I don't think adding another operation vector is a good idea. But I'd
    > rather extend the vma operations vector to deal with all nessecary
    > buts ubstead if addubg a second one.

    Well, there are a lot of users of vm_operations_struct that have no interest in
    the operations in pagetable_operations_struct. Expanding vm_operations_struct
    would increase the size of all VMAs by more than is necessary.

    Also, having the pagetable ops in vm_operations_struct might lead device
    drivers to believe they should be doing something entertaining there. In
    reality, we would only want drivers playing with pagetable_operations when
    they really know what they are doing and why. Having the pagetable_ops
    set is similar to VM_HUGETLB set as a strong sign that something unusual is
    going on that is fairly easy to check for.

    I prefer the additional struct to extending VMAs anyway.

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab
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