linux-kernel - [PATCH v2] mm: simplify find_vma

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Date:	Fri,  9 Dec 2011 16:23:00 -0500
From:	kosaki.motohiro@...il.com
To:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org> (commit_signer:15/23=65%),
	Hugh Dickins <hughd@...gle.com> (commit_signer:7/23=30%),
	Peter Zijlstra <a.p.zijlstra@...llo.nl> (commit_signer:4/23=17%),
	Shaohua Li <shaohua.li@...el.com> (commit_signer:3/23=13%)
Subject: [PATCH v2] mm: simplify find_vma_prev

From: KOSAKI Motohiro <kosaki.motohiro@...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@...fujitsu.com>
---
 mm/mmap.c |   40 +++++++++++-----------------------------
 1 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index eae90af..a84539b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1603,39 +1603,21 @@ 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)
+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;
-
-	/* Go through the RB tree quickly. */
-	rb_node = mm->mm_rb.rb_node;
-
-	while (rb_node) {
-		struct vm_area_struct *vma_tmp;
-		vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);
+	struct vm_area_struct *vma;
 
-		if (addr < vma_tmp->vm_end) {
-			rb_node = rb_node->rb_left;
-		} else {
-			prev = vma_tmp;
-			if (!prev->vm_next || (addr < prev->vm_next->vm_end))
-				break;
-			rb_node = rb_node->rb_right;
-		}
-	}
+	*pprev = NULL;
+	vma = find_vma(mm, addr);
+	if (vma)
+		*pprev = vma->vm_prev;
 
-out:
-	*pprev = prev;
-	return prev ? prev->vm_next : vma;
+	return vma;
 }
 
 /*
-- 
1.7.1

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