[patch 033/158] mm/mmap.c: rb_parent is not necessary in __vma_link_list()

[akpm@linux-foundation.org]

From: Wei Yang <richardw.yang@linux.intel.com>
Subject: mm/mmap.c: rb_parent is not necessary in __vma_link_list()

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@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/internal.h |    2 +-
 mm/mmap.c     |    2 +-
 mm/nommu.c    |    2 +-
 mm/util.c     |    8 ++------
 4 files changed, 5 insertions(+), 9 deletions(-)

--- a/mm/internal.h~mm-mmapc-rb_parent-is-not-necessary-in-__vma_link_list
+++ a/mm/internal.h
@@ -290,7 +290,7 @@ static inline bool is_data_mapping(vm_fl
 
 /* 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
--- a/mm/mmap.c~mm-mmapc-rb_parent-is-not-necessary-in-__vma_link_list
+++ a/mm/mmap.c
@@ -641,7 +641,7 @@ __vma_link(struct mm_struct *mm, struct
 	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);
 }
 
--- a/mm/nommu.c~mm-mmapc-rb_parent-is-not-necessary-in-__vma_link_list
+++ a/mm/nommu.c
@@ -648,7 +648,7 @@ static void add_vma_to_mm(struct mm_stru
 	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);
 }
 
 /*
--- a/mm/util.c~mm-mmapc-rb_parent-is-not-necessary-in-__vma_link_list
+++ a/mm/util.c
@@ -271,7 +271,7 @@ void *memdup_user_nul(const void __user
 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;
 
@@ -280,12 +280,8 @@ void __vma_link_list(struct mm_struct *m
 		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)
_