(12/12/11 8:26 AM), Michal Hocko wrote:
On Fri 09-12-11 17:48:40, kosaki.motohiro@xxxxxxxxx wrote:
From: KOSAKI Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
---
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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