linux-kernel - [PATCH] mm/mmap.c: refine data locality of find_vma

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Date:   Tue,  6 Aug 2019 16:11:23 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     akpm@...ux-foundation.org, mhocko@...e.com, vbabka@...e.cz,
        kirill.shutemov@...ux.intel.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Wei Yang <richardw.yang@...ux.intel.com>
Subject: [PATCH] mm/mmap.c: refine data locality of find_vma_prev

When addr is out of the range of the whole rb_tree, pprev will points to
the biggest node. find_vma_prev gets is by going through the right most
node of the tree.

Since only the last node is the one it is looking for, it is not
necessary to assign pprev to those middle stage nodes. By assigning
pprev to the last node directly, it tries to improve the function
locality a little.

Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
---
 mm/mmap.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 7e8c3e8ae75f..284bc7e51f9c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2271,11 +2271,10 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
 		*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);
+		while (rb_node && rb_node->rb_right)
 			rb_node = rb_node->rb_right;
-		}
+		*pprev = rb_node ? NULL
+			 : rb_entry(rb_node, struct vm_area_struct, vm_rb);
 	}
 	return vma;
 }
-- 
2.17.1