diff --git a/ompi/mca/rcache/rb/rcache_rb.c b/ompi/mca/rcache/rb/rcache_rb.c
index 133e165215..7a057c402e 100644
--- a/ompi/mca/rcache/rb/rcache_rb.c
+++ b/ompi/mca/rcache/rb/rcache_rb.c
@@ -96,14 +96,19 @@ int mca_rcache_rb_insert (
                           uint32_t flags
                           ) { 
     int rc = OMPI_SUCCESS;
-
     OPAL_THREAD_LOCK(&rcache->lock); 
     reg->flags = flags;
-
     if(flags & MCA_MPOOL_FLAGS_CACHE) { 
         rc = mca_rcache_rb_mru_insert( (mca_rcache_rb_module_t*) rcache, reg); 
         if(OMPI_SUCCESS != rc) { 
-            OPAL_THREAD_UNLOCK(&rcache->lock); 
+            OPAL_THREAD_UNLOCK(&rcache->lock);
+            if(OMPI_ERR_TEMP_OUT_OF_RESOURCE == rc) {
+                /* if the registration is too big for the rcache, 
+                   don't cahce it and reset the flags so the upper level 
+                   handles things appropriatly */ 
+                reg->flags = 0;
+                return OMPI_SUCCESS;
+            }
             return rc; 
         }
         OPAL_THREAD_ADD32((int32_t*)&reg->ref_count, 1); 
diff --git a/ompi/mca/rcache/rb/rcache_rb.h b/ompi/mca/rcache/rb/rcache_rb.h
index 64bd38e4f2..6db1003099 100644
--- a/ompi/mca/rcache/rb/rcache_rb.h
+++ b/ompi/mca/rcache/rb/rcache_rb.h
@@ -27,21 +27,21 @@
 #include "ompi/class/ompi_rb_tree.h"
 #include "ompi/mca/rcache/rcache.h"
 
-
 struct mca_rcache_rb_module_t { 
     mca_rcache_base_module_t base; 
     ompi_rb_tree_t rb_tree;
     ompi_free_list_t rb_tree_item_list; 
     opal_list_t mru_list; 
     size_t reg_mru_len; 
-    
+    size_t reg_max_mru_size;
+    size_t reg_cur_mru_size;
+
 };
 typedef struct mca_rcache_rb_module_t mca_rcache_rb_module_t; 
 
 
 struct mca_rcache_rb_component_t { 
     mca_rcache_base_component_t super; 
-    size_t reg_mru_len; 
 }; typedef struct mca_rcache_rb_component_t mca_rcache_rb_component_t; 
 
 OMPI_COMP_EXPORT extern mca_rcache_rb_component_t mca_rcache_rb_component;
diff --git a/ompi/mca/rcache/rb/rcache_rb_component.c b/ompi/mca/rcache/rb/rcache_rb_component.c
index bc416ebe62..f7c04441b1 100644
--- a/ompi/mca/rcache/rb/rcache_rb_component.c
+++ b/ompi/mca/rcache/rb/rcache_rb_component.c
@@ -57,16 +57,27 @@ static int mca_rcache_rb_component_open(void)
 
 mca_rcache_base_module_t* mca_rcache_rb_component_init(void) {
     mca_rcache_rb_module_t* rcache; 
+    
+    rcache = (mca_rcache_rb_module_t*) malloc(sizeof(mca_rcache_rb_module_t));
+    mca_rcache_rb_module_init(rcache);
+ 
     mca_base_param_reg_int(&mca_rcache_rb_component.super.rcache_version, 
                            "mru_len", 
-                           "The maximum size of the MRU (most recently used) rcache list", 
+                           "The maximum size IN ENTRIES of the MRU (most recently used) rcache list", 
                            false, 
                            false, 
                            256, 
-                           (int*)&(mca_rcache_rb_component.reg_mru_len)); 
+                           (int*)&(rcache->reg_mru_len)); 
+    
+    mca_base_param_reg_int(&mca_rcache_rb_component.super.rcache_version, 
+                           "mru_size", 
+                           "The maximum size IN BYTES of the MRU (most recently used) rcache list", 
+                           false, 
+                           false, 
+                           1*1024*1024*1024, /* default to 1GB? */  
+                           (int*)&(rcache->reg_max_mru_size)); 
+
     
-    rcache = (mca_rcache_rb_module_t*) malloc(sizeof(mca_rcache_rb_module_t));
-    mca_rcache_rb_module_init(rcache); 
     return &rcache->base; 
 }
 
diff --git a/ompi/mca/rcache/rb/rcache_rb_mru.c b/ompi/mca/rcache/rb/rcache_rb_mru.c
index 44aadb2373..ffd8a93522 100644
--- a/ompi/mca/rcache/rb/rcache_rb_mru.c
+++ b/ompi/mca/rcache/rb/rcache_rb_mru.c
@@ -29,7 +29,7 @@
  */
 int mca_rcache_rb_mru_init(mca_rcache_rb_module_t* rcache){
     OBJ_CONSTRUCT(&rcache->mru_list, opal_list_t); 
-    rcache->reg_mru_len = mca_rcache_rb_component.reg_mru_len;
+    rcache->reg_cur_mru_size = 0;
     return OMPI_SUCCESS; 
 }
 
@@ -42,6 +42,14 @@ int mca_rcache_rb_mru_insert(
         
                               ) {
     mca_mpool_base_registration_t* old_reg; 
+    size_t reg_size = reg->bound - reg->base + 1;
+    
+    if(reg_size > rcache->reg_max_mru_size) { 
+        return OMPI_ERR_TEMP_OUT_OF_RESOURCE; 
+    }
+    
+    rcache->reg_cur_mru_size += reg_size; 
+
     if(rcache->reg_mru_len <= rcache->mru_list.opal_list_length) {
         /* call deregister - which removes the registration from
          * the tree and mru list. memory will be deregistered when
@@ -55,7 +63,20 @@ int mca_rcache_rb_mru_insert(
         old_reg->mpool->mpool_deregister(old_reg->mpool, old_reg);
         
     }
+    
+    while(rcache->reg_max_mru_size <= rcache->reg_cur_mru_size) { 
+        old_reg = (mca_mpool_base_registration_t*)
+            opal_list_get_first(&rcache->mru_list);
+        /* we need to retain first, because we only want the registration 
+         removed from the tree and the mru */
+        old_reg->mpool->mpool_retain(old_reg->mpool, old_reg);
+        old_reg->mpool->mpool_deregister(old_reg->mpool, old_reg);
+        rcache->reg_cur_mru_size -= (old_reg->bound - old_reg->base + 1);
+                
+    }
+
     opal_list_append(&rcache->mru_list,(opal_list_item_t*) reg); 
+    
     return OMPI_SUCCESS; 
 }