mm: replace vma prio_tree with an interval tree

Implement an interval tree as a replacement for the VMA prio_tree.  The
algorithms are similar to lib/interval_tree.c; however that code can't be
directly reused as the interval endpoints are not explicitly stored in the
VMA.  So instead, the common algorithm is moved into a template and the
details (node type, how to get interval endpoints from the node, etc) are
filled in using the C preprocessor.

Once the interval tree functions are available, using them as a
replacement to the VMA prio tree is a relatively simple, mechanical job.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 61 insertions, 0 deletions

diff --git a/mm/interval_tree.c b/mm/interval_tree.c
new file mode 100644
index 000000000000..7dc565660e56
--- /dev/null
+++ b/mm/interval_tree.c
@@ -0,0 +1,61 @@
+/*
+ * mm/interval_tree.c - interval tree for mapping->i_mmap
+ *
+ * Copyright (C) 2012, Michel Lespinasse <walken@google.com>
+ *
+ * This file is released under the GPL v2.
+ */
+
+#include <linux/mm.h>
+#include <linux/fs.h>
+
+#define ITSTRUCT   struct vm_area_struct
+#define ITRB       shared.linear.rb
+#define ITTYPE     unsigned long
+#define ITSUBTREE  shared.linear.rb_subtree_last
+#define ITSTART(n) ((n)->vm_pgoff)
+#define ITLAST(n)  ((n)->vm_pgoff + \
+                    (((n)->vm_end - (n)->vm_start) >> PAGE_SHIFT) - 1)
+#define ITSTATIC
+#define ITPREFIX   vma_interval_tree
+
+#include <linux/interval_tree_tmpl.h>
+
+/* Insert old immediately after vma in the interval tree */
+void vma_interval_tree_add(struct vm_area_struct *vma,
+                           struct vm_area_struct *old,
+                           struct address_space *mapping)
+{
+        struct rb_node **link;
+        struct vm_area_struct *parent;
+        unsigned long last;
+
+        if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
+                list_add(&vma->shared.nonlinear, &old->shared.nonlinear);
+                return;
+        }
+
+        last = ITLAST(vma);
+
+        if (!old->shared.linear.rb.rb_right) {
+                parent = old;
+                link = &old->shared.linear.rb.rb_right;
+        } else {
+                parent = rb_entry(old->shared.linear.rb.rb_right,
+                                  struct vm_area_struct, shared.linear.rb);
+                if (parent->shared.linear.rb_subtree_last < last)
+                        parent->shared.linear.rb_subtree_last = last;
+                while (parent->shared.linear.rb.rb_left) {
+                        parent = rb_entry(parent->shared.linear.rb.rb_left,
+                                struct vm_area_struct, shared.linear.rb);
+                        if (parent->shared.linear.rb_subtree_last < last)
+                                parent->shared.linear.rb_subtree_last = last;
+                }
+                link = &parent->shared.linear.rb.rb_left;
+        }
+
+        vma->shared.linear.rb_subtree_last = last;
+        rb_link_node(&vma->shared.linear.rb, &parent->shared.linear.rb, link);
+        rb_insert_augmented(&vma->shared.linear.rb, &mapping->i_mmap,
+                            &vma_interval_tree_augment_callbacks);
+}