[patch 127/134] mm/mmap.c: refine find_vma_prev() with rb_last()

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From: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Subject: mm/mmap.c: refine find_vma_prev() with rb_last()

When addr is out of range of the whole rb_tree, pprev will point to the
right-most node.  rb_tree facility already provides a helper function,
rb_last(), to do this task.  We can leverage this instead of
reimplementing it.

This patch refines find_vma_prev() with rb_last() to make it a little
nicer to read.

[akpm@xxxxxxxxxxxxxxxxxxxx: little cleanup, per Vlastimil]
Link: http://lkml.kernel.org/r/20190809001928.4950-1-richardw.yang@xxxxxxxxxxxxxxx
Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/mmap.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/mm/mmap.c~mm-mmapc-refine-find_vma_prev-with-rb_last
+++ a/mm/mmap.c
@@ -2274,12 +2274,9 @@ find_vma_prev(struct mm_struct *mm, unsi
 	if (vma) {
 		*pprev = vma->vm_prev;
 	} else {
-		struct rb_node *rb_node = mm->mm_rb.rb_node;
-		*pprev = NULL;
-		while (rb_node) {
-			*pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
-			rb_node = rb_node->rb_right;
-		}
+		struct rb_node *rb_node = rb_last(&mm->mm_rb);
+
+		*pprev = rb_node ? rb_entry(rb_node, struct vm_area_struct, vm_rb) : NULL;
 	}
 	return vma;
 }
_



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