lib/interval_tree: fast overlap detection

Allow interval trees to quickly check for overlaps to avoid unnecesary
tree lookups in interval_tree_iter_first().

As of this patch, all interval tree flavors will require using a
'rb_root_cached' such that we can have the leftmost node easily
available.  While most users will make use of this feature, those with
special functions (in addition to the generic insert, delete, search
calls) will avoid using the cached option as they can do funky things
with insertions -- for example, vma_interval_tree_insert_after().

[jglisse@redhat.com: fix deadlock from typo vm_lock_anon_vma()]
  Link: http://lkml.kernel.org/r/20170808225719.20723-1-jglisse@redhat.com
Link: http://lkml.kernel.org/r/20170719014603.19029-12-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Doug Ledford <dledford@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Christian Benvenuti <benve@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 55 insertions, 24 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 509434aaf5a4..6111976848ff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -392,7 +392,7 @@ struct address_space {
 	struct radix_tree_root	page_tree;	/* radix tree of all pages */
 	spinlock_t		tree_lock;	/* and lock protecting it */
 	atomic_t		i_mmap_writable;/* count VM_SHARED mappings */
-	struct rb_root		i_mmap;		/* tree of private and shared mappings */
+	struct rb_root_cached	i_mmap;		/* tree of private and shared mappings */
 	struct rw_semaphore	i_mmap_rwsem;	/* protect tree, count, list */
 	/* Protected by tree_lock together with the radix tree */
 	unsigned long		nrpages;	/* number of total pages */
@@ -487,7 +487,7 @@ static inline void i_mmap_unlock_read(struct address_space *mapping)
  */
 static inline int mapping_mapped(struct address_space *mapping)
 {
-	return	!RB_EMPTY_ROOT(&mapping->i_mmap);
+	return	!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root);
 }
 
 /*
diff --git a/include/linux/interval_tree.h b/include/linux/interval_tree.h
index 724556aa3c95..202ee1283f4b 100644
--- a/include/linux/interval_tree.h
+++ b/include/linux/interval_tree.h
@@ -11,13 +11,15 @@ struct interval_tree_node {
 };
 
 extern void
-interval_tree_insert(struct interval_tree_node *node, struct rb_root *root);
+interval_tree_insert(struct interval_tree_node *node,
+		     struct rb_root_cached *root);
 
 extern void
-interval_tree_remove(struct interval_tree_node *node, struct rb_root *root);
+interval_tree_remove(struct interval_tree_node *node,
+		     struct rb_root_cached *root);
 
 extern struct interval_tree_node *
-interval_tree_iter_first(struct rb_root *root,
+interval_tree_iter_first(struct rb_root_cached *root,
 			 unsigned long start, unsigned long last);
 
 extern struct interval_tree_node *
diff --git a/include/linux/interval_tree_generic.h b/include/linux/interval_tree_generic.h
index 58370e1862ad..f096423c8cbd 100644
--- a/include/linux/interval_tree_generic.h
+++ b/include/linux/interval_tree_generic.h
@@ -65,11 +65,13 @@ RB_DECLARE_CALLBACKS(static, ITPREFIX ## _augment, ITSTRUCT, ITRB,	      \
 									      \
 /* Insert / remove interval nodes from the tree */			      \
 									      \
-ITSTATIC void ITPREFIX ## _insert(ITSTRUCT *node, struct rb_root *root)	      \
+ITSTATIC void ITPREFIX ## _insert(ITSTRUCT *node,			      \
+				  struct rb_root_cached *root)	 	      \
 {									      \
-	struct rb_node **link = &root->rb_node, *rb_parent = NULL;	      \
+	struct rb_node **link = &root->rb_root.rb_node, *rb_parent = NULL;    \
 	ITTYPE start = ITSTART(node), last = ITLAST(node);		      \
 	ITSTRUCT *parent;						      \
+	bool leftmost = true;						      \
 									      \
 	while (*link) {							      \
 		rb_parent = *link;					      \
@@ -78,18 +80,22 @@ ITSTATIC void ITPREFIX ## _insert(ITSTRUCT *node, struct rb_root *root)	      \
 			parent->ITSUBTREE = last;			      \
 		if (start < ITSTART(parent))				      \
 			link = &parent->ITRB.rb_left;			      \
-		else							      \
+		else {							      \
 			link = &parent->ITRB.rb_right;			      \
+			leftmost = false;				      \
+		}							      \
 	}								      \
 									      \
 	node->ITSUBTREE = last;						      \
 	rb_link_node(&node->ITRB, rb_parent, link);			      \
-	rb_insert_augmented(&node->ITRB, root, &ITPREFIX ## _augment);	      \
+	rb_insert_augmented_cached(&node->ITRB, root,			      \
+				   leftmost, &ITPREFIX ## _augment);	      \
 }									      \
 									      \
-ITSTATIC void ITPREFIX ## _remove(ITSTRUCT *node, struct rb_root *root)	      \
+ITSTATIC void ITPREFIX ## _remove(ITSTRUCT *node,			      \
+				  struct rb_root_cached *root)		      \
 {									      \
-	rb_erase_augmented(&node->ITRB, root, &ITPREFIX ## _augment);	      \
+	rb_erase_augmented_cached(&node->ITRB, root, &ITPREFIX ## _augment);  \
 }									      \
 									      \
 /*									      \
@@ -140,15 +146,35 @@ ITPREFIX ## _subtree_search(ITSTRUCT *node, ITTYPE start, ITTYPE last)	      \
 }									      \
 									      \
 ITSTATIC ITSTRUCT *							      \
-ITPREFIX ## _iter_first(struct rb_root *root, ITTYPE start, ITTYPE last)      \
+ITPREFIX ## _iter_first(struct rb_root_cached *root,			      \
+			ITTYPE start, ITTYPE last)			      \
 {									      \
-	ITSTRUCT *node;							      \
+	ITSTRUCT *node, *leftmost;					      \
 									      \
-	if (!root->rb_node)						      \
+	if (!root->rb_root.rb_node)					      \
 		return NULL;						      \
-	node = rb_entry(root->rb_node, ITSTRUCT, ITRB);			      \
+									      \
+	/*								      \
+	 * Fastpath range intersection/overlap between A: [a0, a1] and	      \
+	 * B: [b0, b1] is given by:					      \
+	 *								      \
+	 *         a0 <= b1 && b0 <= a1					      \
+	 *								      \
+	 *  ... where A holds the lock range and B holds the smallest	      \
+	 * 'start' and largest 'last' in the tree. For the later, we	      \
+	 * rely on the root node, which by augmented interval tree	      \
+	 * property, holds the largest value in its last-in-subtree.	      \
+	 * This allows mitigating some of the tree walk overhead for	      \
+	 * for non-intersecting ranges, maintained and consulted in O(1).     \
+	 */								      \
+	node = rb_entry(root->rb_root.rb_node, ITSTRUCT, ITRB);		      \
 	if (node->ITSUBTREE < start)					      \
 		return NULL;						      \
+									      \
+	leftmost = rb_entry(root->rb_leftmost, ITSTRUCT, ITRB);		      \
+	if (ITSTART(leftmost) > last)					      \
+		return NULL;						      \
+									      \
 	return ITPREFIX ## _subtree_search(node, start, last);		      \
 }									      \
 									      \
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5195e272fc4a..f8c10d336e42 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2034,13 +2034,13 @@ extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
 
 /* interval_tree.c */
 void vma_interval_tree_insert(struct vm_area_struct *node,
-			      struct rb_root *root);
+			      struct rb_root_cached *root);
 void vma_interval_tree_insert_after(struct vm_area_struct *node,
 				    struct vm_area_struct *prev,
-				    struct rb_root *root);
+				    struct rb_root_cached *root);
 void vma_interval_tree_remove(struct vm_area_struct *node,
-			      struct rb_root *root);
-struct vm_area_struct *vma_interval_tree_iter_first(struct rb_root *root,
+			      struct rb_root_cached *root);
+struct vm_area_struct *vma_interval_tree_iter_first(struct rb_root_cached *root,
 				unsigned long start, unsigned long last);
 struct vm_area_struct *vma_interval_tree_iter_next(struct vm_area_struct *node,
 				unsigned long start, unsigned long last);
@@ -2050,11 +2050,12 @@ struct vm_area_struct *vma_interval_tree_iter_next(struct vm_area_struct *node,
 	     vma; vma = vma_interval_tree_iter_next(vma, start, last))
 
 void anon_vma_interval_tree_insert(struct anon_vma_chain *node,
-				   struct rb_root *root);
+				   struct rb_root_cached *root);
 void anon_vma_interval_tree_remove(struct anon_vma_chain *node,
-				   struct rb_root *root);
-struct anon_vma_chain *anon_vma_interval_tree_iter_first(
-	struct rb_root *root, unsigned long start, unsigned long last);
+				   struct rb_root_cached *root);
+struct anon_vma_chain *
+anon_vma_interval_tree_iter_first(struct rb_root_cached *root,
+				  unsigned long start, unsigned long last);
 struct anon_vma_chain *anon_vma_interval_tree_iter_next(
 	struct anon_vma_chain *node, unsigned long start, unsigned long last);
 #ifdef CONFIG_DEBUG_VM_RB
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index f8ca2e74b819..733d3d8181e2 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -55,7 +55,9 @@ struct anon_vma {
 	 * is serialized by a system wide lock only visible to
 	 * mm_take_all_locks() (mm_all_locks_mutex).
 	 */
-	struct rb_root rb_root;	/* Interval tree of private "related" vmas */
+
+	/* Interval tree of private "related" vmas */
+	struct rb_root_cached rb_root;
 };
 
 /*