Make the anon_vma list lock a read/write lock.  Heaviest use of this
lock is in the page_referenced()/try_to_unmap() calls from vmscan
[shrink_page_list()].  These functions can use a read lock to allow
some parallelism for different cpus trying to reclaim pages mapped
via the same set of vmas.

This change should not change the footprint of the anon_vma in the
non-debug case.

Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by:  Rik van Riel <riel@redhat.com>

Index: Linux/include/linux/rmap.h
===================================================================
--- Linux.orig/include/linux/rmap.h	2007-11-28 10:54:36.000000000 -0500
+++ Linux/include/linux/rmap.h	2007-11-28 11:12:37.000000000 -0500
@@ -25,7 +25,7 @@
  * pointing to this anon_vma once its vma list is empty.
  */
 struct anon_vma {
-	spinlock_t lock;	/* Serialize access to vma list */
+	rwlock_t rwlock;	/* Serialize access to vma list */
 	struct list_head head;	/* List of private "related" vmas */
 };
 
@@ -43,18 +43,21 @@ static inline void anon_vma_free(struct 
 	kmem_cache_free(anon_vma_cachep, anon_vma);
 }
 
+/*
+ * This needs to be a write lock for __vma_link()
+ */
 static inline void anon_vma_lock(struct vm_area_struct *vma)
 {
 	struct anon_vma *anon_vma = vma->anon_vma;
 	if (anon_vma)
-		spin_lock(&anon_vma->lock);
+		write_lock(&anon_vma->rwlock);
 }
 
 static inline void anon_vma_unlock(struct vm_area_struct *vma)
 {
 	struct anon_vma *anon_vma = vma->anon_vma;
 	if (anon_vma)
-		spin_unlock(&anon_vma->lock);
+		write_unlock(&anon_vma->rwlock);
 }
 
 /*
Index: Linux/mm/rmap.c
===================================================================
--- Linux.orig/mm/rmap.c	2007-11-28 10:54:37.000000000 -0500
+++ Linux/mm/rmap.c	2007-11-28 11:12:37.000000000 -0500
@@ -25,7 +25,7 @@
  *   mm->mmap_sem
  *     page->flags PG_locked (lock_page)
  *       mapping->i_mmap_lock
- *         anon_vma->lock
+ *         anon_vma->rwlock
  *           mm->page_table_lock or pte_lock
  *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
  *             swap_lock (in swap_duplicate, swap_info_get)
@@ -68,7 +68,7 @@ int anon_vma_prepare(struct vm_area_stru
 		if (anon_vma) {
 			allocated = NULL;
 			locked = anon_vma;
-			spin_lock(&locked->lock);
+			write_lock(&locked->rwlock);
 		} else {
 			anon_vma = anon_vma_alloc();
 			if (unlikely(!anon_vma))
@@ -87,7 +87,7 @@ int anon_vma_prepare(struct vm_area_stru
 		spin_unlock(&mm->page_table_lock);
 
 		if (locked)
-			spin_unlock(&locked->lock);
+			write_unlock(&locked->rwlock);
 		if (unlikely(allocated))
 			anon_vma_free(allocated);
 	}
@@ -113,9 +113,9 @@ void anon_vma_link(struct vm_area_struct
 	struct anon_vma *anon_vma = vma->anon_vma;
 
 	if (anon_vma) {
-		spin_lock(&anon_vma->lock);
+		write_lock(&anon_vma->rwlock);
 		list_add_tail(&vma->anon_vma_node, &anon_vma->head);
-		spin_unlock(&anon_vma->lock);
+		write_unlock(&anon_vma->rwlock);
 	}
 }
 
@@ -127,12 +127,12 @@ void anon_vma_unlink(struct vm_area_stru
 	if (!anon_vma)
 		return;
 
-	spin_lock(&anon_vma->lock);
+	write_lock(&anon_vma->rwlock);
 	list_del(&vma->anon_vma_node);
 
 	/* We must garbage collect the anon_vma if it's empty */
 	empty = list_empty(&anon_vma->head);
-	spin_unlock(&anon_vma->lock);
+	write_unlock(&anon_vma->rwlock);
 
 	if (empty)
 		anon_vma_free(anon_vma);
@@ -142,7 +142,7 @@ static void anon_vma_ctor(struct kmem_ca
 {
 	struct anon_vma *anon_vma = data;
 
-	spin_lock_init(&anon_vma->lock);
+ 	rwlock_init(&anon_vma->rwlock);
 	INIT_LIST_HEAD(&anon_vma->head);
 }
 
@@ -169,7 +169,7 @@ static struct anon_vma *page_lock_anon_v
 		goto out;
 
 	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
-	spin_lock(&anon_vma->lock);
+	read_lock(&anon_vma->rwlock);
 	return anon_vma;
 out:
 	rcu_read_unlock();
@@ -178,7 +178,7 @@ out:
 
 static void page_unlock_anon_vma(struct anon_vma *anon_vma)
 {
-	spin_unlock(&anon_vma->lock);
+	read_unlock(&anon_vma->rwlock);
 	rcu_read_unlock();
 }
 
Index: Linux/mm/mmap.c
===================================================================
--- Linux.orig/mm/mmap.c	2007-11-28 10:54:36.000000000 -0500
+++ Linux/mm/mmap.c	2007-11-28 11:12:37.000000000 -0500
@@ -564,7 +564,7 @@ again:			remove_next = 1 + (end > next->
 	if (vma->anon_vma)
 		anon_vma = vma->anon_vma;
 	if (anon_vma) {
-		spin_lock(&anon_vma->lock);
+		write_lock(&anon_vma->rwlock);
 		/*
 		 * Easily overlooked: when mprotect shifts the boundary,
 		 * make sure the expanding vma has anon_vma set if the
@@ -618,7 +618,7 @@ again:			remove_next = 1 + (end > next->
 	}
 
 	if (anon_vma)
-		spin_unlock(&anon_vma->lock);
+		write_unlock(&anon_vma->rwlock);
 	if (mapping)
 		spin_unlock(&mapping->i_mmap_lock);
 
Index: Linux/mm/migrate.c
===================================================================
--- Linux.orig/mm/migrate.c	2007-11-28 10:54:36.000000000 -0500
+++ Linux/mm/migrate.c	2007-11-28 11:12:37.000000000 -0500
@@ -229,12 +229,12 @@ static void remove_anon_migration_ptes(s
 	 * We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
 	 */
 	anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
-	spin_lock(&anon_vma->lock);
+	read_lock(&anon_vma->rwlock);
 
 	list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
 		remove_migration_pte(vma, old, new);
 
-	spin_unlock(&anon_vma->lock);
+	read_unlock(&anon_vma->rwlock);
 }
 
 /*

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