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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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