From 4fc6dbabcf58279f00582f212daa1a44d40eeca3 Mon Sep 17 00:00:00 2001
From: Wei Yang <richardw.yang@linux.intel.com>
Date: Sat, 30 Nov 2019 17:50:53 -0800
Subject: [PATCH] mm/mmap.c: rb_parent is not necessary in __vma_link_list()

References: bnc#1155780 (VM/FS functional and performance backports)
Patch-mainline: v5.5-rc1
Git-commit: aba6dfb75fe15650991442efd137c32fbf2e2b85

Now we use rb_parent to get next, while this is not necessary.

When prev is NULL, this means vma should be the first element in the list.
Then next should be current first one (mm->mmap), no matter whether we
have parent or not.

After removing it, the code shows the beauty of symmetry.

Link: http://lkml.kernel.org/r/20190813032656.16625-1-richardw.yang@linux.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 mm/internal.h | 2 +-
 mm/mmap.c     | 2 +-
 mm/nommu.c    | 2 +-
 mm/util.c     | 8 ++------
 4 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index c8262b173754..074592588556 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -293,7 +293,7 @@ static inline bool is_data_mapping(vm_flags_t flags)
 
 /* mm/util.c */
 void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
-		struct vm_area_struct *prev, struct rb_node *rb_parent);
+		struct vm_area_struct *prev);
 void __vma_unlink_list(struct mm_struct *mm, struct vm_area_struct *vma);
 
 #ifdef CONFIG_MMU
diff --git a/mm/mmap.c b/mm/mmap.c
index 008683d32231..cebd101b3227 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -632,7 +632,7 @@ __vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
 	struct vm_area_struct *prev, struct rb_node **rb_link,
 	struct rb_node *rb_parent)
 {
-	__vma_link_list(mm, vma, prev, rb_parent);
+	__vma_link_list(mm, vma, prev);
 	__vma_link_rb(mm, vma, rb_link, rb_parent);
 }
 
diff --git a/mm/nommu.c b/mm/nommu.c
index c422e182dff4..1a403f65b99e 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -637,7 +637,7 @@ static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
 	if (rb_prev)
 		prev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
 
-	__vma_link_list(mm, vma, prev, parent);
+	__vma_link_list(mm, vma, prev);
 }
 
 /*
diff --git a/mm/util.c b/mm/util.c
index 796065f0eebf..5f113cd0acad 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -264,7 +264,7 @@ void *memdup_user_nul(const void __user *src, size_t len)
 EXPORT_SYMBOL(memdup_user_nul);
 
 void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
-		struct vm_area_struct *prev, struct rb_node *rb_parent)
+		struct vm_area_struct *prev)
 {
 	struct vm_area_struct *next;
 
@@ -273,12 +273,8 @@ void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
 		next = prev->vm_next;
 		prev->vm_next = vma;
 	} else {
+		next = mm->mmap;
 		mm->mmap = vma;
-		if (rb_parent)
-			next = rb_entry(rb_parent,
-					struct vm_area_struct, vm_rb);
-		else
-			next = NULL;
 	}
 	vma->vm_next = next;
 	if (next)