Add debugging information to debug travis failures.

cont.c

@@ -185,7 +185,8 @@ fiber_pool_expand(struct fiber_pool * fiber_pool, size_t size, size_t count)
     allocation->base = NULL;
     allocation->size = size;
     allocation->count = count;
-
+
+    fprintf(stderr, "\nfiber_pool_expand: %p, %zu x [%zu]\n", fiber_pool, count, size);
 
 #ifdef _WIN32
     DWORD old_protect;
@@ -330,7 +331,7 @@ fiber_pool_stack_acquire(struct fiber_pool * fiber_pool) {
 
     fiber_pool_stack_reset(&vacancy->stack);
 
-    // printf("\nfiber_pool_stack_acquire: %p, next=%p\n", vacancy->stack.base, fiber_pool->vacancies);
+    fprintf(stderr, "\nfiber_pool_stack_acquire: %p, next=%p\n", vacancy->stack.base, fiber_pool->vacancies);
 
     return vacancy->stack;
 }
@@ -341,13 +342,13 @@ fiber_pool_stack_release(struct fiber_pool_stack stack) {
 
     // Using madvise can make physical memory available to OS when there is memory pressure.
     // But bencmarks show that this approach makes performance worse.
-    // madvise(vacancy->stack.base, vacancy->stack.size - RB_PAGE_SIZE, MADV_FREE);
+    madvise(vacancy->stack.base, vacancy->stack.size - RB_PAGE_SIZE, MADV_FREE);
 
     vacancy->stack = stack;
     vacancy->next = stack.pool->vacancies;
     stack.pool->vacancies = vacancy;
 
-    // printf("\nfiber_pool_stack_release: %p\n", vacancy->stack.base);
+    fprintf(stderr, "\nfiber_pool_stack_release: %p\n", vacancy->stack.base);
 }
 
 static COROUTINE