diff --git a/plageq.c b/plageq.c
index be0141a..a743a5b 100644
--- a/plageq.c
+++ b/plageq.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <stdlib.h>
+#include <sys/mman.h>
 #include <string.h>
 #include <error.h>
 #include <errno.h>
@@ -17,8 +17,6 @@ struct node {
 typedef struct node *iptree;
 typedef void (*bitsfun)(bits, mask_t, mask_t, mask_t);
 
-pos_t maxpos = 0;
-
 void clearb(uint8_t *b) {
 	bzero(b, DEPTHB);
 }
@@ -41,24 +39,37 @@ int getb(uint8_t *b, int n) {
 }
 
 iptree iptree_new(pos_t size) {
-	iptree t = malloc(size * sizeof(struct node));
-	if (t == 0) error(1, errno, "iptree_new: malloc failed");
-	pos_t i;
-	for(i = 0; i < size; ++i) {
-		t[i].a[0] = i + 1;
-		t[i].a[1] = 0;
-		clearb(t[i].b);
-	}
-	t[i].a[0] = 0;
+	// use mmap to get pages lazily and zeroed
+	iptree t = mmap(0, size * sizeof(struct node), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+	if (t == MAP_FAILED) error(1, errno, "iptree_new: mmap failed");
+	// use 2 queues of free nodes
+	t[0].a[0] = 1; // start of continuous range
+	t[0].a[1] = 0; // pointer to a chain of free nodes
+	t[size - 1].a[0] = 1; // end of countinous range marker
 	return t;
 }
 
 pos_t iptree_popfree(iptree t) {
-	pos_t f = t[0].a[0];
-	if (f > maxpos) maxpos = f;
-	if (!f) error(1, 0, "iptree_popfree: no free nodes left");
-	t[0].a[0] = t[f].a[0];
-	t[f].a[0] = 0;
+	pos_t f;
+	if (t[0].a[1]) {
+		// try from chain first
+		f = t[0].a[1];
+		t[0].a[1] = t[f].a[0]; // shift pointer to the next node
+		t[f].a[0] = 0; // clear popped element
+	} else if (t[0].a[0]) {
+		// then try if something is left in continuous range
+		f = t[0].a[0]; // start of the range
+		if (t[f].a[0]) {
+			// this is the last element
+			t[0].a[0] = 0;
+			t[f].a[0] = 0; // celar popped element
+		} else {
+			// more elements are there in the range
+			++(t[0].a[0]);
+		}
+	} else {
+		if (!f) error(1, 0, "iptree_popfree: no free nodes left");
+	}
 	return f;
 }
 
@@ -211,6 +222,7 @@ int main(void) {
 	iptree_traverse(t, ip4, print4);
 	iptree_traverse(t, ip6, print6);
 
+	pos_t maxpos = t[0].a[0] ? t[0].a[0] : SIZE;
 	double mb_used = nodes2mb(maxpos);
 	double mb_all = nodes2mb(SIZE);
 	fprintf(stderr, "max nodes: %.2f%%, %d / %d, %.2fMB / %.2fMB\n", maxpos / (double)SIZE * 100.0, maxpos, SIZE, mb_used, mb_all);
diff --git a/plagmax.c b/plagmax.c
index 4d6108b..95f0ed5 100644
--- a/plagmax.c
+++ b/plagmax.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <stdlib.h>
+#include <sys/mman.h>
 #include <string.h>
 #include <error.h>
 #include <errno.h>
@@ -11,33 +11,46 @@ struct node { pos_t a[2]; };
 typedef struct node *iptree;
 typedef void (*bitsfun)(bits, mask_t);
 
-pos_t maxpos = 0;
-
 iptree iptree_new(pos_t size) {
-	iptree t = malloc(size * sizeof(struct node));
-	if (t == 0) error(1, errno, "iptree_new: malloc failed");
-	pos_t i;
-	for(i = 0; i < size; ++i) {
-		t[i].a[0] = i + 1;
-		t[i].a[1] = 0;
-	}
-	t[i].a[0] = 0;
+	// use mmap to get pages lazily and zeroed
+	iptree t = mmap(0, size * sizeof(struct node), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+	if (t == MAP_FAILED) error(1, errno, "iptree_new: mmap failed");
+	// use 2 queues of free nodes
+	t[0].a[0] = 1; // start of continuous range
+	t[0].a[1] = 0; // pointer to a chain of free nodes
+	t[size - 1].a[0] = 1; // end of countinous range marker
 	return t;
 }
 
 pos_t iptree_popfree(iptree t) {
-	pos_t f = t[0].a[0];
-	if (f > maxpos) maxpos = f;
-	if (!f) error(1, 0, "iptree_popfree: no free nodes left");
-	t[0].a[0] = t[f].a[0];
-	t[f].a[0] = 0;
+	pos_t f;
+	if (t[0].a[1]) {
+		// try from chain first
+		f = t[0].a[1];
+		t[0].a[1] = t[f].a[0]; // shift pointer to the next node
+		t[f].a[0] = 0; // clear popped element
+	} else if (t[0].a[0]) {
+		// then try if something is left in continuous range
+		f = t[0].a[0]; // start of the range
+		if (t[f].a[0]) {
+			// this is the last element
+			t[0].a[0] = 0;
+			t[f].a[0] = 0; // celar popped element
+		} else {
+			// more elements are there in the range
+			++(t[0].a[0]);
+		}
+	} else {
+		error(1, 0, "iptree_popfree: no free nodes left");
+	}
 	return f;
 }
 
 void iptree_pushfree(iptree t, pos_t f) {
-	t[f].a[0] = t[0].a[0];
-	t[f].a[1] = 0;
-	t[0].a[0] = f;
+	// elements are pushed only to the pointer chain
+	t[f].a[0] = t[0].a[1]; // pointer to current head
+	t[f].a[1] = 0; // clear remaining fields
+	t[0].a[1] = f; // redirect the pointer to new head
 }
 
 int iptree_is_term(iptree t, pos_t h) {
@@ -191,6 +204,7 @@ int main(void) {
 	iptree_traverse(t, ip4, print4);
 	iptree_traverse(t, ip6, print6);
 
+	pos_t maxpos = t[0].a[0] ? t[0].a[0] : SIZE;
 	double mb_used = nodes2mb(maxpos);
 	double mb_all = nodes2mb(SIZE);
 	fprintf(stderr, "max nodes: %.2f%%, %d / %d, %.2fMB / %.2fMB\n", maxpos / (double)SIZE * 100.0, maxpos, SIZE, mb_used, mb_all);