message: meshable-arena: re-order loops in findPages
diff: @@ -156,10 +156,18 @@ bool MeshableArena::findPagesInner(internal::vector<Span> freeSpans[kSpanClassCo
  }
  bool MeshableArena::findPages(Length pageCount, Span &result) {
  + // Search through all dirty spans first. We don't worry about
  + // fragmenting dirty pages, as being able to reuse dirty pages means
  + // we don't increase RSS.
  for (size_t i = Span(0, pageCount).spanClass(); i < kSpanClassCount; i++) {
  if (findPagesInner(_dirty, i, pageCount, result)) {
  return true;
  }
  + }
  +
  + // if no dirty pages are avaiable, search clean pages. An allocated
  + // clean page (once it is written to) means an increased RSS.
  + for (size_t i = Span(0, pageCount).spanClass(); i < kSpanClassCount; i++) {
  if (findPagesInner(_clean, i, pageCount, result)) {
  return true;
  }
  