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    SubjectRe: [PATCH v3] mm: simplify find_vma_prev
    (12/12/11 8:26 AM), Michal Hocko wrote:
    > On Fri 09-12-11 17:48:40, kosaki.motohiro@gmail.com wrote:
    >> From: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
    >>
    >> commit 297c5eee37 (mm: make the vma list be doubly linked) added
    >> vm_prev member into vm_area_struct. Therefore we can simplify
    >> find_vma_prev() by using it. Also, this change help to improve
    >> page fault performance because it has strong locality of reference.
    >>
    >> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
    >> ---
    >> mm/mmap.c | 36 ++++++++----------------------------
    >> 1 files changed, 8 insertions(+), 28 deletions(-)
    >>
    >> diff --git a/mm/mmap.c b/mm/mmap.c
    >> index eae90af..b9c0241 100644
    >> --- a/mm/mmap.c
    >> +++ b/mm/mmap.c
    >> @@ -1603,39 +1603,19 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
    >>
    >> EXPORT_SYMBOL(find_vma);
    >>
    >> -/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
    >> +/*
    >> + * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
    >> + * Note: pprev is set to NULL when return value is NULL.
    >> + */
    >> struct vm_area_struct *
    >> find_vma_prev(struct mm_struct *mm, unsigned long addr,
    >> struct vm_area_struct **pprev)
    >> {
    >> - struct vm_area_struct *vma = NULL, *prev = NULL;
    >> - struct rb_node *rb_node;
    >> - if (!mm)
    >> - goto out;
    >> -
    >> - /* Guard against addr being lower than the first VMA */
    >> - vma = mm->mmap;
    >
    > Why have you removed this guard? Previously we had pprev==NULL and
    > returned mm->mmap.
    > This seems like a semantic change without any explanation. Could you
    > clarify?

    IIUC, find_vma_prev() is module unexported and none of known caller use
    pprev==NULL. Thus, I thought it can be also simplified. Am I missing
    something?



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