augmented rbtree: add new RB_DECLARE_CALLBACKS_MAX macro

Add RB_DECLARE_CALLBACKS_MAX, which generates augmented rbtree callbacks
for the case where the augmented value is a scalar whose definition
follows a max(f(node)) pattern.  This actually covers all present uses of
RB_DECLARE_CALLBACKS, and saves some (source) code duplication in the
various RBCOMPUTE function definitions.

[walken@google.com: fix mm/vmalloc.c]
  Link: http://lkml.kernel.org/r/CANN689FXgK13wDYNh1zKxdipeTuALG4eKvKpsdZqKFJ-rvtGiQ@mail.gmail.com
[walken@google.com: re-add check to check_augmented()]
  Link: http://lkml.kernel.org/r/20190727022027.GA86863@google.com
Link: http://lkml.kernel.org/r/20190703040156.56953-3-walken@google.com
Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/pat_rbtree.c

@@ -54,23 +54,10 @@ static u64 get_subtree_max_end(struct rb_node *node)
 	return ret;
 }
 
-static u64 compute_subtree_max_end(struct memtype *data)
-{
-	u64 max_end = data->end, child_max_end;
+#define NODE_END(node) ((node)->end)
 
-	child_max_end = get_subtree_max_end(data->rb.rb_right);
-	if (child_max_end > max_end)
-		max_end = child_max_end;
-
-	child_max_end = get_subtree_max_end(data->rb.rb_left);
-	if (child_max_end > max_end)
-		max_end = child_max_end;
-
-	return max_end;
-}
-
-RB_DECLARE_CALLBACKS(static, memtype_rb_augment_cb, struct memtype, rb,
-		     u64, subtree_max_end, compute_subtree_max_end)
+RB_DECLARE_CALLBACKS_MAX(static, memtype_rb_augment_cb,
+			 struct memtype, rb, u64, subtree_max_end, NODE_END)
 
 /* Find the first (lowest start addr) overlapping range from rb tree */
 static struct memtype *memtype_rb_lowest_match(struct rb_root *root,