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>

mm/mmap.c

@@ -289,9 +289,9 @@ out:
 	return retval;
 }
 
-static long vma_compute_subtree_gap(struct vm_area_struct *vma)
+static inline unsigned long vma_compute_gap(struct vm_area_struct *vma)
 {
-	unsigned long max, prev_end, subtree_gap;
+	unsigned long gap, prev_end;
 
 	/*
 	 * Note: in the rare case of a VM_GROWSDOWN above a VM_GROWSUP, we
@@ -299,14 +299,21 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma)
 	 * an unmapped area; whereas when expanding we only require one.
 	 * That's a little inconsistent, but keeps the code here simpler.
 	 */
-	max = vm_start_gap(vma);
+	gap = vm_start_gap(vma);
 	if (vma->vm_prev) {
 		prev_end = vm_end_gap(vma->vm_prev);
-		if (max > prev_end)
-			max -= prev_end;
+		if (gap > prev_end)
+			gap -= prev_end;
 		else
-			max = 0;
+			gap = 0;
 	}
+	return gap;
+}
+
+#ifdef CONFIG_DEBUG_VM_RB
+static unsigned long vma_compute_subtree_gap(struct vm_area_struct *vma)
+{
+	unsigned long max = vma_compute_gap(vma), subtree_gap;
 	if (vma->vm_rb.rb_left) {
 		subtree_gap = rb_entry(vma->vm_rb.rb_left,
 				struct vm_area_struct, vm_rb)->rb_subtree_gap;
@@ -322,7 +329,6 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma)
 	return max;
 }
 
-#ifdef CONFIG_DEBUG_VM_RB
 static int browse_rb(struct mm_struct *mm)
 {
 	struct rb_root *root = &mm->mm_rb;
@@ -428,8 +434,9 @@ static void validate_mm(struct mm_struct *mm)
 #define validate_mm(mm) do { } while (0)
 #endif
 
-RB_DECLARE_CALLBACKS(static, vma_gap_callbacks, struct vm_area_struct, vm_rb,
-		     unsigned long, rb_subtree_gap, vma_compute_subtree_gap)
+RB_DECLARE_CALLBACKS_MAX(static, vma_gap_callbacks,
+			 struct vm_area_struct, vm_rb,
+			 unsigned long, rb_subtree_gap, vma_compute_gap)
 
 /*
  * Update augmented rbtree rb_subtree_gap values after vma->vm_start or
@@ -439,8 +446,8 @@ RB_DECLARE_CALLBACKS(static, vma_gap_callbacks, struct vm_area_struct, vm_rb,
 static void vma_gap_update(struct vm_area_struct *vma)
 {
 	/*
-	 * As it turns out, RB_DECLARE_CALLBACKS() already created a callback
-	 * function that does exactly what we want.
+	 * As it turns out, RB_DECLARE_CALLBACKS_MAX() already created
+	 * a callback function that does exactly what we want.
 	 */
 	vma_gap_callbacks_propagate(&vma->vm_rb, NULL);
 }

mm/vmalloc.c

@@ -396,9 +396,8 @@ compute_subtree_max_size(struct vmap_area *va)
 		get_subtree_max_size(va->rb_node.rb_right));
 }
 
-RB_DECLARE_CALLBACKS(static, free_vmap_area_rb_augment_cb,
-	struct vmap_area, rb_node, unsigned long, subtree_max_size,
-	compute_subtree_max_size)
+RB_DECLARE_CALLBACKS_MAX(static, free_vmap_area_rb_augment_cb,
+	struct vmap_area, rb_node, unsigned long, subtree_max_size, va_size)
 
 static void purge_vmap_area_lazy(void);
 static BLOCKING_NOTIFIER_HEAD(vmap_notify_list);