--- ../plan3/pf.c.vm3	2016-10-30 12:20:23.834100000 +1300
+++ ../plan3/pf.c.vm3	2016-11-02 20:15:08.147099000 +1300
@@ -59,6 +59,7 @@ 
 #include <sys/sysctl.h>
 #include <sys/taskqueue.h>
 #include <sys/ucred.h>
+#include <sys/proc.h>
 
 #include <net/if.h>
 #include <net/if_var.h>
@@ -777,12 +778,34 @@ 
 	struct pf_keyhash	*kh;
 	struct pf_idhash	*ih;
 	struct pf_srchash	*sh;
+        u_long hw_physmem;
 	u_int i;
-
-	if (pf_hashsize == 0 || !powerof2(pf_hashsize))
+        size_t size;
+        
+	/* Get the available hardware memory */
+        size=sizeof(hw_physmem);
+        if (kernel_sysctlbyname(&thread0, "hw.physmem", &hw_physmem,	\
+	&size, 0, 0, 0, 0) != 0)
+	/* make the check against hw.physmem irrelevant */
+		hw_physmem = ULONG_MAX; 
+
+	if (pf_hashsize == 0 || !powerof2(pf_hashsize) || 		\
+	(pf_hashsize * sizeof(struct pf_keyhash)) > hw_physmem || 	\
+	(pf_hashsize * sizeof(struct pf_idhash)) > hw_physmem){
+		printf("pf: Invalid states hash table size : %lu. "
+			"Using the default value %lu.\n", 
+			(unsigned long)pf_hashsize,
+			(unsigned long)PF_HASHSIZ);
 		pf_hashsize = PF_HASHSIZ;
-	if (pf_srchashsize == 0 || !powerof2(pf_srchashsize))
+	}
+	if (pf_srchashsize == 0 || !powerof2(pf_srchashsize) || 	\
+	(pf_srchashsize * sizeof(struct pf_srchash)) > hw_physmem ){
+		printf("pf: Invalid source node hash table size : %lu. "
+			"Using the default value %lu.\n", 
+			(unsigned long)pf_srchashsize,
+			(unsigned long)(PF_HASHSIZ/4));
 		pf_srchashsize = PF_HASHSIZ / 4;
+	}
 
 	V_pf_hashseed = arc4random();