On Thu, Jun 21, 2012 at 05:57:09PM -0400, Rik van Riel wrote:

+			if (!vma->vm_prev) {
+				/* This is the left-most VMA. */
+				if (vma->vm_start - len >= lower_limit) {
+					addr = lower_limit;
+					goto found_addr;
+				}
+			} else {
+				/* Is this gap large enough? Remember it. */
+				vma_start = max(vma->vm_prev->vm_end, lower_limit);
+				if (vma->vm_start - len >= vma_start) {
+					addr = vma_start;
+					found_here = true;
+				}
+			}

You could unify these two cases:

			vma_start = lower_limit;
			if (vma->vm_prev && vma->vm_prev->vm_end > vma_start)
				vma_start = vma->vm_prev->vm_end;
			if (vma->vm_start - len >= vma_start) {
				addr = vma_start;
				found_here = true;
			}

You don't need the goto found_addr; the search won't be going left as there
is no node there and it won't be going right as found_here is true.

We may also be albe to dispense with found_here and replace it with a special
value (either NULL or something not page aligned) for addr.

+		if (!found_here && node_free_gap(rb_node->rb_right) >= len) {
+			/* Last known gap is to the right of this subtree. */
+			rb_node = rb_node->rb_right;
+			continue;
+		} else if (!addr) {
+			rb_node = rb_find_next_uncle(rb_node);
+			continue;
 		}

Looks like you're already using my suggestion of using !addr to indicate
we haven't found a suitable gap yet :)

I don't think we want to visit just any uncle though - we want to visit one
that has a large enough free gap somewhere in its subtree.

So, maybe:

		if (!found_here) {	// or if(!addr) or whatever
			struct rb_node *rb_prev = NULL;
			do {
				if (rb_node != rb_prev &&
				    node_free_gap(rb_node->rb_right) >= len) {
					rb_node = rb_node->rb_right;
					break;
				}
				rb_prev = rb_node;
				rb_node = rb_parent(rb_node);
			} while (rb_node);
			continue;
		}

+		/* This is the left-most gap. */
+		goto found_addr;
 	}
+
+	/*
+	 * There is not enough space to the left of any VMA.
+	 * Check the far right-hand side of the VMA tree.
+	 */
+	rb_node = mm->mm_rb.rb_node;
+	while (rb_node->rb_right)
+		rb_node = rb_node->rb_right;
+	vma = rb_to_vma(rb_node);
+	addr = vma->vm_end;
+
+	/*
+	 * The right-most VMA ends below the lower limit. Can only happen
+	 * if a binary personality loads the stack below the executable.
+	 */
+	if (addr < lower_limit)
+		addr = lower_limit;
+
+ found_addr:
+	if (TASK_SIZE - len < addr)
+		return -ENOMEM;

I'm confused - if we come from 'goto found_addr', we found a gap to the
left of an existing vma; aren't we guaranteed that this gap ends to the
left of TASK_SIZE too since the existing vma's vm_begin should be
less than TASK_SIZE ?

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

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