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    SubjectRe: Always passing mm and vma down (was: [RFC][PATCH] Convert do_no_page() to a hook to avoid DFS race)
    On Sat, May 31, 2003 at 10:46:18AM +0200, Ingo Oeser wrote:
    > On Fri, May 30, 2003 at 04:41:50PM -0700, Paul E. McKenney wrote:
    > > -struct page *
    > > -ia32_install_shared_page (struct vm_area_struct *vma, unsigned long address, int no_share)
    > > +int
    > > +ia32_install_shared_page (struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access, pmd_t *pmd)
    > Why do we always pass mm and vma down, even if vma->vm_mm
    > contains the mm, where the vma belongs to? Is the connection
    > between a vma and its mm also protected by the mmap_sem?
    > Is this really necessary or an oversight and we waste a lot of
    > stack in a lot of places?
    > If we just need it for accounting: We need current->mm, if we
    > need it to locate the next vma relatively to this vma, vma->vm_mm
    > is the one.

    Interesting point. The original do_no_page() API does this
    as well:

    static int
    do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
    unsigned long address, int write_access, pte_t *page_table, pmd_t *pmd)

    As does do_anonymous_page(). I assumed that there were corner
    cases where this one-to-one correspondence did not exist, but
    must confess that I did not go looking for them.

    Or is this a performance issue, avoiding a dereference and
    possible cache miss?

    Thanx, Paul
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