coll/han: alltoall uses han freelist when possible

As an optimization, when the han alltoall algorithm is forced to
allocate a bounce buffer, and that bounce buffer is small enough, then
use a buffer from the han_component.pack_buffers free list.

Signed-off-by: Luke Robison <lrbison@amazon.com>

Author: Luke Robison

ompi/mca/coll/han/coll_han_alltoall.c

@@ -72,6 +72,12 @@ int mca_coll_han_alltoall_using_smsc(
     opal_convertor_t convertor;
     int send_needs_bounce, have_device_buffer;
     size_t packed_size = 0;
+    enum {
+        BOUNCE_NOT_INITIALIZED = 0,
+        BOUNCE_IS_FROM_RBUF = 1,
+        BOUNCE_IS_FROM_FREELIST = 2,
+        BOUNCE_IS_FROM_MALLOC = 3,
+    };
 
 
     OPAL_OUTPUT_VERBOSE((90, mca_coll_han_component.han_output,
@@ -191,7 +197,7 @@ int mca_coll_han_alltoall_using_smsc(
 
       If the application buffer is device memory, we'll also need to exchange
       in push mode so that the process which has device registrations can
-      perform the reads.
+      perform the reads. (this mode has been disabled)
 
       In both of these cases, we'll need to use the bounce buffer too.
     */
@@ -211,19 +217,30 @@ int mca_coll_han_alltoall_using_smsc(
     inter_recv_reqs = malloc(sizeof(*inter_recv_reqs) * up_size );
     char **low_bufs = malloc(low_size * sizeof(*low_bufs));
     void **sbuf_map_ctx = malloc(low_size * sizeof(&sbuf_map_ctx));
+    opal_free_list_item_t *send_fl_item = NULL;
 
     const int nptrs_gather = 3;
     void **gather_buf_out = calloc(low_size*nptrs_gather, sizeof(void*));
-    bool send_bounce_is_allocated = false;
+    int send_bounce_status = BOUNCE_NOT_INITIALIZED;
 
     do {
 start_allgather:
         if ( 0 == send_needs_bounce ) {
             send_bounce = (char*)rbuf + up_rank*send_bytes_per_fan;
+            send_bounce_status = BOUNCE_IS_FROM_RBUF;
         } else {
-            if (!send_bounce_is_allocated) {
-                send_bounce = malloc(send_bytes_per_fan * fanout);
-                send_bounce_is_allocated = true;
+            if (send_bounce_status == BOUNCE_NOT_INITIALIZED || send_bounce_status == BOUNCE_IS_FROM_RBUF) {
+                if (send_bytes_per_fan * fanout < mca_coll_han_component.han_packbuf_bytes) {
+                    send_fl_item = opal_free_list_get(&mca_coll_han_component.pack_buffers);
+                    if (send_fl_item) {
+                        send_bounce_status = BOUNCE_IS_FROM_FREELIST;
+                        send_bounce = send_fl_item->ptr;
+                    }
+                }
+                if (!send_fl_item) {
+                    send_bounce = malloc(send_bytes_per_fan * fanout);
+                    send_bounce_status = BOUNCE_IS_FROM_MALLOC;
+                }
             }
         }
 
@@ -409,7 +426,11 @@ int mca_coll_han_alltoall_using_smsc(
         }
     }
     OBJ_DESTRUCT(&convertor);
-    if (send_bounce_is_allocated) free(send_bounce);
+    if (send_bounce_status == BOUNCE_IS_FROM_FREELIST) {
+        opal_free_list_return(&mca_coll_han_component.pack_buffers, send_fl_item);
+    } else if (send_bounce_status == BOUNCE_IS_FROM_MALLOC) {
+        free(send_bounce);
+    }
     free(inter_send_reqs);
     free(inter_recv_reqs);
     free(sbuf_map_ctx);