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>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 0618cd85b862..b874c4761e84 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -391,7 +391,7 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
                  * Leave empty anon_vmas on the list - we'll need
                  * to free them outside the lock.
                  */
-                if (RB_EMPTY_ROOT(&anon_vma->rb_root)) {
+                if (RB_EMPTY_ROOT(&anon_vma->rb_root.rb_root)) {
                         anon_vma->parent->degree--;
                         continue;
                 }
@@ -425,7 +425,7 @@ static void anon_vma_ctor(void *data)
 
         init_rwsem(&anon_vma->rwsem);
         atomic_set(&anon_vma->refcount, 0);
-        anon_vma->rb_root = RB_ROOT;
+        anon_vma->rb_root = RB_ROOT_CACHED;
 }
 
 void __init anon_vma_init(void)