kern_descrip.patch

--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -130,7 +130,8 @@ static int  getmaxfd(struct thread *td);
  * resource limit).
  *
  * Since threads may hold references to individual descriptor table
- * entries, the tables are never freed.  Instead, they are placed on a
+ * entries, the tables are only freed if a process has one thread and
+ * the table has not been shared. Otherwise, they are placed on a
  * linked list and freed only when the struct filedesc is released.
  */
 #define NDFILE         20
@@ -1540,6 +1541,7 @@ fdgrowtable(struct filedesc *fdp, int nfd)
        struct freetable *ft;
        struct fdescenttbl *ntable;
        struct fdescenttbl *otable;
+       struct proc *p = curthread->td_proc;
        int nnfiles, onfiles;
        NDSLOTTYPE *nmap, *omap;
 
@@ -1601,19 +1603,24 @@ fdgrowtable(struct filedesc *fdp, int nfd)
        atomic_store_rel_ptr((volatile void *)&fdp->fd_files, (uintptr_t)ntable);
 
        /*
-        * Do not free the old file table, as some threads may still
-        * reference entries within it.  Instead, place it on a freelist
-        * which will be processed when the struct filedesc is released.
+        * If a the current process only has one thread, and the file
+        * table is not shared, we can free the old file table. Otherwise
+        * we place it on a freelist which will be processed when the
+        * struct filedesc is released.
         *
         * Note that if onfiles == NDFILE, we're dealing with the original
         * static allocation contained within (struct filedesc0 *)fdp,
         * which must not be freed.
         */
        if (onfiles > NDFILE) {
-               ft = (struct freetable *)&otable->fdt_ofiles[onfiles];
-               fdp0 = (struct filedesc0 *)fdp;
-               ft->ft_table = otable;
-               SLIST_INSERT_HEAD(&fdp0->fd_free, ft, ft_next);
+               if (fdp->fd_refcnt==1 && p->p_numthreads==1) {
+                       free(otable, M_FILEDESC);
+               } else {
+                       ft = (struct freetable *)&otable->fdt_ofiles[onfiles];
+                       ft->ft_table = otable;
+                       fdp0 = (struct filedesc0 *)fdp;
+                       SLIST_INSERT_HEAD(&fdp0->fd_free, ft, ft_next);
+               }
        }
        /*
         * The map does not have the same possibility of threads still