--- ad_lustre_aggregate.c	2009-07-02 17:19:27.000000000 +0200
+++ ad_lustre_aggregate.c.new	2010-01-14 14:58:15.000000000 +0100
@@ -22,9 +22,8 @@
      *  striping_info[1]: stripe_count
      *  striping_info[2]: avail_cb_nodes
      */
-    int stripe_size, stripe_count, CO = 1, CO_max = 1, CO_nodes, lflag;
+    int stripe_size, stripe_count, CO = 1;
     int avail_cb_nodes, divisor, nprocs_for_coll = fd->hints->cb_nodes;
-    char *value = (char *) ADIOI_Malloc((MPI_MAX_INFO_VAL + 1) * sizeof(char));
 
     /* Get hints value */
     /* stripe size */
@@ -33,9 +32,7 @@
     /* stripe_size and stripe_count have been validated in ADIOI_LUSTRE_Open() */
     stripe_count = fd->hints->striping_factor;
 
-    /* Calculate the available number of I/O clients, that is
-     *  avail_cb_nodes=min(cb_nodes, stripe_count*CO), where
-     *  CO=1 by default
+    /* Calculate the available number of I/O clients
      */
     if (!mode) {
         /* for collective read,
@@ -47,32 +44,43 @@
 	CO = 1;
 	/*XXX: maybe there are other better way for collective read */
     } else {
-        /* CO_max: the largest number of IO clients for each ost group */
-        CO_max = (nprocs_for_coll - 1)/ stripe_count + 1;
         /* CO also has been validated in ADIOI_LUSTRE_Open(), >0 */
 	CO = fd->hints->fs_hints.lustre.co_ratio;
-	CO = ADIOI_MIN(CO_max, CO);
     }
+
     /* Calculate how many IO clients we need */
     /* To avoid extent lock conflicts,
-     * avail_cb_nodes should divide (stripe_count*CO) exactly,
-     * so that each OST is accessed by only one or more constant clients. */
-    CO_nodes = stripe_count * CO;
-    avail_cb_nodes = ADIOI_MIN(nprocs_for_coll, CO_nodes);
-    if (avail_cb_nodes ==  CO_nodes) {
-        do {
-            /* find the divisor of CO_nodes */
-            divisor = 1;
-            do {
-                divisor ++;
-            } while (CO_nodes % divisor);
-            CO_nodes = CO_nodes / divisor;
-            /* if stripe_count*CO is a prime number, change nothing */
-            if ((CO_nodes <= avail_cb_nodes) && (CO_nodes != 1)) {
-                avail_cb_nodes = CO_nodes;
-                break;
-            }
-        } while (CO_nodes != 1);
+     * avail_cb_nodes should either be a multiple of stripe_count,
+                             or divide stripe_count exactly.
+     * so that each OST is accessed by a maximum of CO constant clients. */
+
+    if (nprocs_for_coll >= stripe_count)
+        /* avail_cb_nodes should be a multiple of stripe_count and the number of procs per OST
+           should be limited to the minimum between nprocs_for_coll/stripe_count and CO
+           e.g. if stripe_count=20, nprocs_for_coll=42 and CO=3 then avail_cb_nodes should be egal to 40 */
+        avail_cb_nodes = stripe_count * ADIOI_MIN(nprocs_for_coll/stripe_count, CO);
+    else {
+        /* nprocs_for_coll is less than stripe_count */
+        /* avail_cb_nodes should divide stripe_count */
+        /* e.g. if stripe_count=60 and nprocs_for_coll=8 then avail_cb_nodes should be egal to 6 */
+        /* This could be done with :
+                while (stripe_count % avail_cb_nodes != 0) avail_cb_nodes--;
+           but this can be optimized for large values of nprocs_for_coll and stripe_count */
+        divisor = 2;
+        avail_cb_nodes = 1;
+        /* try to divise */
+        while (stripe_count >= divisor*divisor) {
+                if ((stripe_count % divisor) == 0) {
+                        if (stripe_count/divisor <= nprocs_for_coll) {
+                                /* The value is found ! */
+                                avail_cb_nodes = stripe_count/divisor;
+                                break;
+                        }
+                        /* if divisor is less than nprocs_for_coll, divisor is a solution, but it is not sure that it is the best one */
+                        else if (divisor <= nprocs_for_coll) avail_cb_nodes = divisor;
+                }
+        divisor++;
+        }
     }
 
     *striping_info_ptr = (int *) ADIOI_Malloc(3 * sizeof(int));
@@ -80,8 +88,6 @@
     striping_info[0] = stripe_size;
     striping_info[1] = stripe_count;
     striping_info[2] = avail_cb_nodes;
-
-    ADIOI_Free(value);
 }
 
 int ADIOI_LUSTRE_Calc_aggregator(ADIO_File fd, ADIO_Offset off,