port r11516 from 1.1: considerably reduce the amount of requests submitted at the same time. Pushing more does not seem to really improve performance, and on the contrary increases the latency of possibly urging requests

src/datawizard/data_request.c

@@ -24,8 +24,8 @@
  * Data interfaces should also have to declare how many asynchronous requests
  * they have actually started (think of e.g. csr).
  */
-#define MAX_PENDING_REQUESTS_PER_NODE 400
-#define MAX_PENDING_PREFETCH_REQUESTS_PER_NODE 200
+#define MAX_PENDING_REQUESTS_PER_NODE 20
+#define MAX_PENDING_PREFETCH_REQUESTS_PER_NODE 10
 
 /* requests that have not been treated at all */
 static struct _starpu_data_request_list *data_requests[STARPU_MAXNODES];