diff --git a/TODO b/TODO
index f7c22a7..690b4ce 100644
--- a/TODO
+++ b/TODO
@@ -15,8 +15,8 @@ CLEANUP
 
 BUGS
 	* fast input or slow output -> blocks pile up, huge memory usage
+		* performance lags under IO?
 	* slow input -> CPUs idle while waiting for input
-	* performance lags under IO?
 
 EFFICIENCY
 	* should use ordered list in collator
diff --git a/common.c b/common.c
index d5c0534..2c8f38a 100644
--- a/common.c
+++ b/common.c
@@ -218,9 +218,10 @@ void *decode_block_start(off_t block_seek) {
     return bw;
 }
 
-queue_t *queue_new(void) {
+queue_t *queue_new(queue_free_t freer) {
     queue_t *q = malloc(sizeof(queue_t));
     q->first = q->last = NULL;
+    q->freer = freer;
     pthread_mutex_init(&q->mutex, NULL);
     pthread_cond_init(&q->pop_cond, NULL);
     return q;
@@ -229,7 +230,8 @@ queue_t *queue_new(void) {
 void queue_free(queue_t *q) {
     for (queue_item_t *i = q->first; i; ) {
         queue_item_t *tmp = i->next;
-        free(i->data);
+        if (q->freer)
+            q->freer(i->type, i->data);
         free(i);
         i = tmp;
     }
diff --git a/pixz.h b/pixz.h
index 2f687f8..fd4f3cd 100644
--- a/pixz.h
+++ b/pixz.h
@@ -36,12 +36,16 @@ struct queue_item_t {
     queue_item_t *next;
 };
 
+typedef void (*queue_free_t)(int type, void *p);
+
 typedef struct {
     queue_item_t *first;
     queue_item_t *last;
     
     pthread_mutex_t mutex;
     pthread_cond_t pop_cond;
+    
+    queue_free_t freer;
 } queue_t;
 
 
@@ -70,8 +74,7 @@ void read_file_index(void);
 void dump_file_index(void);
 void free_file_index(void);
 
-queue_t *queue_new(void);
+queue_t *queue_new(queue_free_t freer);
 void queue_free(queue_t *q);
-// data should be on heap, if present
 void queue_push(queue_t *q, int type, void *data);
 int queue_pop(queue_t *q, void **datap);
diff --git a/write.c b/write.c
index 72aa758..d8f46ec 100644
--- a/write.c
+++ b/write.c
@@ -27,7 +27,7 @@ struct io_block_t {
 static size_t gNumEncodeThreads = 0;
 static pthread_t *gEncodeThreads = NULL;
 static pthread_t gReadThread;
-static queue_t *gEncodeQ, *gWriteQ;
+static queue_t *gReadQ, *gEncodeQ, *gWriteQ;
 static size_t gBlockInSize = 0, gBlockOutSize = 0;
 
 static off_t gMultiHeaderStart = 0;
@@ -47,7 +47,7 @@ static size_t gFileIndexBufPos = 0;
 
 static void *read_thread(void *data);
 static void *encode_thread(void *data);
-
+static void block_queue_free(int type, void *p);
 
 static bool is_multi_header(const char *name);
 static void add_file(off_t offset, const char *name);
@@ -90,8 +90,16 @@ int main(int argc, char **argv) {
     // thread setup
     gNumEncodeThreads = num_threads();
     gEncodeThreads = malloc(gNumEncodeThreads * sizeof(pthread_t));
-    gEncodeQ = queue_new();
-    gWriteQ = queue_new();
+    gReadQ = queue_new(block_queue_free);
+    gEncodeQ = queue_new(block_queue_free);
+    gWriteQ = queue_new(block_queue_free);
+    for (size_t i = 0; i < (int)(gNumEncodeThreads * 2 + 4); ++i) {
+        // create blocks, including a margin of error
+        io_block_t *ib = malloc(sizeof(io_block_t));
+        ib->input = malloc(gBlockInSize);
+        ib->output = malloc(gBlockOutSize);
+        queue_push(gReadQ, MSG_BLOCK, ib);
+    }
     if (pthread_create(&gReadThread, NULL, &read_thread, NULL))
         die("Error creating read thread");
     for (int i = 0; i < gNumEncodeThreads; ++i) {
@@ -133,6 +141,7 @@ int main(int argc, char **argv) {
         die("Error joining read thread");
     queue_free(gEncodeQ);
     queue_free(gWriteQ);
+    queue_free(gReadQ);
     free(gEncodeThreads);
     
     return 0;
@@ -167,13 +176,9 @@ static void *read_thread(void *data) {
     
     // write last block, if necessary
     if (gReadBlock) {
-        if (gReadBlock->insize) {
-            queue_push(gEncodeQ, MSG_BLOCK, gReadBlock);
-        } else { // if this block had only one read, and it was EOF
-            free(gReadBlock->input);
-            free(gReadBlock->output);
-            free(gReadBlock);
-        }
+        // if this block had only one read, and it was EOF, it's waste
+        queue_push(gReadBlock->insize ? gEncodeQ : gReadQ, MSG_BLOCK, gReadBlock);
+        gReadBlock = NULL;
     }
     
     // stop the other threads
@@ -191,9 +196,7 @@ static void *read_thread(void *data) {
 
 static ssize_t tar_read(struct archive *ar, void *ref, const void **bufp) {
     if (!gReadBlock) {
-        gReadBlock = malloc(sizeof(io_block_t));
-        gReadBlock->input = malloc(gBlockInSize);
-        gReadBlock->output = malloc(gBlockOutSize);
+        queue_pop(gReadQ, (void**)&gReadBlock);
         gReadBlock->insize = 0;
         gReadBlock->seq = gBlockNum++;
     }
@@ -251,6 +254,22 @@ static void add_file(off_t offset, const char *name) {
     gLastFile = f;
 }
 
+static void block_queue_free(int type, void *p) {
+    switch (type) {
+        case MSG_BLOCK: {
+            io_block_t *ib = (io_block_t*)p;
+            free(ib->input);
+            free(ib->output);
+            free(ib);
+            break;
+        }
+        case MSG_STOP:
+            break;
+        default:
+            die("Unknown msg type %d", type);
+    }
+}
+
 
 #pragma mark ENCODING
 
@@ -324,9 +343,7 @@ static void write_blocks(io_block_t **ibs, size_t *seq) {
                 } else {
                     *ibs = ib->next;
                 }
-                free(ib->input);
-                free(ib->output);
-                free(ib);
+                queue_push(gReadQ, MSG_BLOCK, ib);
                 
                 ++*seq;
                 block_missing = false;