3 files changed, 663 insertions, 78 deletions

diff --git a/src/plugins/unittest/svm_fifo_test.c b/src/plugins/unittest/svm_fifo_test.c
index d2afc36e0d0..7d83b105c93 100644
--- a/src/plugins/unittest/svm_fifo_test.c
+++ b/src/plugins/unittest/svm_fifo_test.c
@@ -1456,8 +1456,403 @@ cleanup:
     }
 
   svm_fifo_free (f);
+  vec_free (test_data);
+  vec_free (data_buf);
+  return 0;
+}
+
+static int
+chunk_list_len (svm_fifo_chunk_t * c)
+{
+  svm_fifo_chunk_t *it;
+  int count = 0;
+
+  if (!c)
+    return 0;
+
+  count = 1;
+  it = c->next;
+  while (it && it != c)
+    {
+      it = it->next;
+      count++;
+    }
+  return count;
+}
+
+static void
+chunk_list_free (svm_fifo_chunk_t * c, svm_fifo_chunk_t * stop)
+{
+  svm_fifo_chunk_t *it, *next;
+
+  it = c;
+  while (it && it != stop)
+    {
+      next = it->next;
+      clib_mem_free (it);
+      it = next;
+    }
+}
+
+static void
+chunk_list_splice (svm_fifo_chunk_t * a, svm_fifo_chunk_t * b)
+{
+  svm_fifo_chunk_t *it;
+
+  it = a;
+  while (it->next)
+    it = it->next;
+  it->next = b;
+}
+
+static int
+sfifo_test_fifo_shrink (vlib_main_t * vm, unformat_input_t * input)
+{
+  int __clib_unused verbose = 0, fifo_size = 101, chunk_size = 100;
+  int i, rv, test_n_bytes, diff, deq_bytes;
+  svm_fifo_chunk_t *c, *prev, *collected;
+  u8 *test_data = 0, *data_buf = 0;
+  svm_fifo_t *f;
 
+  while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
+    {
+      if (unformat (input, "verbose"))
+	verbose = 1;
+      else
+	{
+	  vlib_cli_output (vm, "parse error: '%U'", format_unformat_error,
+			   input);
+	  return -1;
+	}
+    }
+
+  /*
+   * Init fifo with multiple chunks
+   */
+  f = fifo_prepare (fifo_size);
+  svm_fifo_init_pointers (f, 0, 0);
+
+  prev = 0;
+  for (i = 0; i < 11; i++)
+    {
+      c = clib_mem_alloc (sizeof (svm_fifo_chunk_t) + chunk_size);
+      c->length = 100;
+      c->start_byte = ~0;
+      c->next = prev;
+      prev = c;
+    }
+
+  svm_fifo_add_chunk (f, c);
+  SFIFO_TEST (f->size == 12 * chunk_size + 1, "size expected %u is %u",
+	      12 * chunk_size + 1, f->size);
+
+  /*
+   * No fifo wrap and no chunk used (one chunk)
+   */
+  rv = svm_fifo_reduce_size (f, chunk_size, 0);
+  SFIFO_TEST (rv == chunk_size, "len expected %u is %u", chunk_size, rv);
+  SFIFO_TEST (f->size == 12 * chunk_size + 1, "size expected %u is %u",
+	      12 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+
+  /* Check enqueue space to force size reduction */
+  (void) svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_COLLECT_CHUNKS, "collect flag should"
+	      " be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_SHRINK), "shrink flag should not be"
+	      " set");
+
+  collected = c = svm_fifo_collect_chunks (f);
+  rv = chunk_list_len (c);
+  SFIFO_TEST (rv == 1, "expected %u chunks got %u", 1, rv);
+  rv = chunk_list_len (f->start_chunk);
+  SFIFO_TEST (rv == 11, "expected %u chunks got %u", 11, rv);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /*
+   * Fifo wrap and multiple chunks used
+   */
+
+  /* Init test data and fifo */
+  test_n_bytes = f->nitems;
+  vec_validate (test_data, test_n_bytes - 1);
+  vec_validate (data_buf, vec_len (test_data));
+
+  for (i = 0; i < vec_len (test_data); i++)
+    test_data[i] = i;
+
+  svm_fifo_init_pointers (f, f->size / 2, f->size / 2);
+  for (i = 0; i < test_n_bytes; i++)
+    {
+      rv = svm_fifo_enqueue (f, sizeof (u8), &test_data[i]);
+      if (rv < 0)
+	SFIFO_TEST (0, "enqueue returned");
+    }
+
+  /* Try to reduce fifo size with fifo full */
+  rv = svm_fifo_reduce_size (f, 3.5 * chunk_size, 0);
+  SFIFO_TEST (rv == 3 * chunk_size, "len expected %u is %u", 3 * chunk_size,
+	      rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+
+  /* Check enqueue space to try size reduction. Should not work */
+  rv = svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (rv == 0, "free space expected %u is %u", 0, rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /* Dequeue byte-by-byte up to last byte on last chunk */
+  deq_bytes = f->size - f->size / 2 - 1;
+  for (i = 0; i < deq_bytes; i++)
+    {
+      (void) svm_fifo_max_enqueue (f);
+      rv = svm_fifo_dequeue (f, 1, &data_buf[i]);
+      if (rv < 0)
+	SFIFO_TEST (0, "dequeue returned");
+    }
+
+  rv = svm_fifo_max_enqueue (f);
+
+  /* We've dequeued more than 3*chunk_size so nitems should be updated */
+  SFIFO_TEST (f->nitems == 8 * chunk_size, "nitems expected %u is %u",
+	      8 * chunk_size, f->nitems);
+  /* Free space should be what was dequeued - 3 * chunk_size, which was
+   * consumed by shrinking the fifo */
+  diff = deq_bytes - 3 * chunk_size;
+  SFIFO_TEST (rv == diff, "free space expected %u is %u", diff, rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /* Dequeue one more such that head goes beyond last chunk */
+  rv = svm_fifo_dequeue (f, 1, &data_buf[deq_bytes]);
+  if (rv < 0)
+    SFIFO_TEST (0, "dequeue returned");
+
+  rv = svm_fifo_max_enqueue (f);
+  SFIFO_TEST (f->nitems == 8 * chunk_size, "nitems expected %u is %u",
+	      8 * chunk_size, f->nitems);
+  SFIFO_TEST (rv == diff + 1, "free space expected %u is %u", diff + 1, rv);
+  SFIFO_TEST (f->size == 8 * chunk_size + 1, "size expected %u is %u",
+	      8 * chunk_size + 1, f->size);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_SHRINK), "shrink flag should not be"
+	      " set");
+  SFIFO_TEST (f->flags & SVM_FIFO_F_COLLECT_CHUNKS, "collect flag should"
+	      " be set");
+
+  /* Dequeue the rest of the data */
+  deq_bytes += 1;
+  for (i = 0; i < test_n_bytes - deq_bytes; i++)
+    {
+      rv = svm_fifo_dequeue (f, 1, &data_buf[i + deq_bytes]);
+      if (rv < 0)
+	SFIFO_TEST (0, "dequeue returned");
+    }
+
+  rv = svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (f->size == 8 * chunk_size + 1, "size expected %u is %u",
+	      8 * chunk_size + 1, f->size);
+  SFIFO_TEST (rv == 8 * chunk_size, "free space expected %u is %u",
+	      8 * chunk_size, rv);
+
+  rv = compare_data (data_buf, test_data, 0, vec_len (test_data),
+		     (u32 *) & i);
+  if (rv)
+    SFIFO_TEST (0, "[%d] dequeued %u expected %u", i, data_buf[i],
+		test_data[i]);
+
+  c = svm_fifo_collect_chunks (f);
+  rv = chunk_list_len (c);
+  SFIFO_TEST (rv == 3, "expected %u chunks got %u", 3, rv);
+  rv = chunk_list_len (f->start_chunk);
+  SFIFO_TEST (rv == 8, "expected %u chunks got %u", 8, rv);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /*
+   * OOO segment on chunk that should be removed
+   */
+
+  svm_fifo_add_chunk (f, c);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+
+  memset (data_buf, 0, vec_len (data_buf));
+  svm_fifo_init_pointers (f, f->size / 2, f->size / 2);
+  svm_fifo_enqueue (f, 200, test_data);
+  svm_fifo_enqueue_with_offset (f, 50, vec_len (test_data) - 250,
+				&test_data[250]);
+
+  /* Free space */
+  rv = svm_fifo_max_enqueue (f);
+  SFIFO_TEST (rv == vec_len (test_data) - 200, "free space expected %u is %u",
+	      vec_len (test_data) - 200, rv);
+
+  /* Ask to reduce size */
+  rv = svm_fifo_reduce_size (f, 3.5 * chunk_size, 0);
+  SFIFO_TEST (rv == 3 * chunk_size, "len expected %u is %u", 3 * chunk_size,
+	      rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+
+  /* Try to force size reduction but it should fail */
+  rv = svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (rv == vec_len (test_data) - 200, "free space expected %u is %u",
+	      vec_len (test_data) - 200, rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /* Dequeue the in order data. This should shrink nitems */
+  rv = svm_fifo_dequeue (f, 200, data_buf);
+  if (rv < 0)
+    SFIFO_TEST (0, "dequeue returned");
+
+  rv = svm_fifo_max_enqueue (f);
+  SFIFO_TEST (rv == vec_len (test_data) - 200, "free space expected %u is %u",
+	      vec_len (test_data) - 200, rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->nitems == 11 * chunk_size - 200, "nitems expected %u is %u",
+	      11 * chunk_size - 200, f->nitems);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /* Enqueue the missing 50 bytes. Fifo will become full */
+  rv = svm_fifo_enqueue (f, 50, &test_data[200]);
+  SFIFO_TEST (rv == vec_len (test_data) - 200, "free space expected %u is %u",
+	      vec_len (test_data) - 200, rv);
+
+  rv = svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (rv == 0, "free space expected %u is %u", 0, rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+
+  /* Dequeue a chunk and check nitems shrink but fifo still full */
+  svm_fifo_dequeue (f, 100, &data_buf[200]);
+
+  rv = svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (rv == 0, "free space expected %u is %u", 0, rv);
+  SFIFO_TEST (f->size == 11 * chunk_size + 1, "size expected %u is %u",
+	      11 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->nitems == 11 * chunk_size - 300, "nitems expected %u is %u",
+	      11 * chunk_size - 300, f->nitems);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  /* Dequeue enough to unwrap the fifo */
+  deq_bytes = f->size - f->size / 2 - 300;
+  svm_fifo_dequeue (f, deq_bytes, &data_buf[300]);
+  rv = svm_fifo_max_enqueue (f);
+
+  /* Overall we've dequeued deq_bytes + 300, but fifo size shrunk 300 */
+  SFIFO_TEST (rv == 300 + deq_bytes - 300, "free space expected %u is %u",
+	      300 + deq_bytes - 300, rv);
+  SFIFO_TEST (f->size == 8 * chunk_size + 1, "size expected %u is %u",
+	      8 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->nitems == 8 * chunk_size, "nitems expected %u is %u",
+	      8 * chunk_size, f->nitems);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_SHRINK), "shrink flag should not be"
+	      " set");
+  SFIFO_TEST (f->flags & SVM_FIFO_F_COLLECT_CHUNKS, "collect flag should"
+	      " be set");
+
+  /* Dequeue the rest */
+  svm_fifo_dequeue (f, test_n_bytes / 2, &data_buf[300 + deq_bytes]);
+  rv = compare_data (data_buf, test_data, 0, vec_len (test_data),
+		     (u32 *) & i);
+  if (rv)
+    SFIFO_TEST (0, "[%d] dequeued %u expected %u", i, data_buf[i],
+		test_data[i]);
+
+  c = svm_fifo_collect_chunks (f);
+  rv = chunk_list_len (c);
+  SFIFO_TEST (rv == 3, "expected %u chunks got %u", 3, rv);
+  rv = chunk_list_len (f->start_chunk);
+  SFIFO_TEST (rv == 8, "expected %u chunks got %u", 8, rv);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  chunk_list_splice (collected, c);
+
+  /*
+   * Remove all chunks possible
+   */
+  svm_fifo_init_pointers (f, 601, 601);
+  rv = svm_fifo_reduce_size (f, 8 * chunk_size, 1);
+  SFIFO_TEST (rv == 7 * chunk_size, "actual len expected %u is %u",
+	      7 * chunk_size, rv);
+  SFIFO_TEST (f->size == 6 * chunk_size + 1, "size expected %u is %u",
+	      6 * chunk_size + 1, f->size);
+  SFIFO_TEST (f->nitems == 1 * chunk_size, "nitems expected %u is %u",
+	      1 * chunk_size, f->nitems);
+  SFIFO_TEST (f->flags & SVM_FIFO_F_SHRINK, "shrink flag should be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+
+  rv = svm_fifo_max_enqueue (f);
+  SFIFO_TEST (rv == chunk_size, "free space expected %u is %u", chunk_size,
+	      rv);
+
+  /* Force head/tail to move to first chunk */
+  svm_fifo_enqueue (f, 1, test_data);
+  svm_fifo_dequeue (f, 1, data_buf);
+  rv = svm_fifo_max_enqueue (f);
+
+  SFIFO_TEST (rv == chunk_size, "free space expected %u is %u", chunk_size,
+	      rv);
+  SFIFO_TEST (f->size == chunk_size + 1, "size expected %u is %u",
+	      chunk_size + 1, f->size);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_SHRINK), "shrink flag should not be"
+	      " set");
+  SFIFO_TEST (f->flags & SVM_FIFO_F_COLLECT_CHUNKS, "collect flag should"
+	      " be set");
+
+  c = svm_fifo_collect_chunks (f);
+  rv = chunk_list_len (c);
+  SFIFO_TEST (rv == 7, "expected %u chunks got %u", 7, rv);
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_COLLECT_CHUNKS), "collect flag should"
+	      " not be set");
+  SFIFO_TEST (!(f->flags & SVM_FIFO_F_MULTI_CHUNK), "multi-chunk flag should"
+	      " not be set");
+
+  chunk_list_splice (collected, c);
+
+  /*
+   * Cleanup
+   */
+
+  chunk_list_free (f->start_chunk->next, f->start_chunk);
+  chunk_list_free (collected, 0);
+  svm_fifo_free (f);
+  vec_free (test_data);
   vec_free (data_buf);
+
   return 0;
 }
 
@@ -1876,6 +2271,8 @@ svm_fifo_test (vlib_main_t * vm, unformat_input_t * input,
 	res = sfifo_test_fifo_replay (vm, input);
       else if (unformat (input, "grow"))
 	res = sfifo_test_fifo_grow (vm, input);
+      else if (unformat (input, "shrink"))
+	res = sfifo_test_fifo_shrink (vm, input);
       else if (unformat (input, "segment"))
 	res = sfifo_test_fifo_segment (vm, input);
       else if (unformat (input, "all"))
@@ -1934,6 +2331,9 @@ svm_fifo_test (vlib_main_t * vm, unformat_input_t * input,
 	  if ((res = sfifo_test_fifo_grow (vm, input)))
 	    goto done;
 
+	  if ((res = sfifo_test_fifo_shrink (vm, input)))
+	    goto done;
+
 	  str = "all";
 	  unformat_init_cstring (input, str);
 	  if ((res = sfifo_test_fifo_segment (vm, input)))
diff --git a/src/svm/svm_fifo.c b/src/svm/svm_fifo.c
index d5638777290..e017b619d15 100644
--- a/src/svm/svm_fifo.c
+++ b/src/svm/svm_fifo.c
@@ -135,7 +135,7 @@ svm_fifo_free_ooo_data (svm_fifo_t * f)
 }
 
 static inline ooo_segment_t *
-ooo_segment_get_prev (svm_fifo_t * f, ooo_segment_t * s)
+ooo_segment_prev (svm_fifo_t * f, ooo_segment_t * s)
 {
   if (s->prev == OOO_SEGMENT_INVALID_INDEX)
     return 0;
@@ -222,7 +222,7 @@ ooo_segment_add (svm_fifo_t * f, u32 offset, u32 head, u32 tail, u32 length)
     s = pool_elt_at_index (f->ooo_segments, s->next);
 
   /* If we have a previous and we overlap it, use it as starting point */
-  prev = ooo_segment_get_prev (f, s);
+  prev = ooo_segment_prev (f, s);
   if (prev
       && position_leq (f, offset_pos, ooo_segment_end_pos (f, prev), tail))
     {
@@ -374,6 +374,20 @@ ooo_segment_try_collect (svm_fifo_t * f, u32 n_bytes_enqueued, u32 * tail)
   return bytes;
 }
 
+static ooo_segment_t *
+ooo_segment_last (svm_fifo_t * f)
+{
+  ooo_segment_t *s;
+
+  if (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX)
+    return 0;
+
+  s = svm_fifo_first_ooo_segment (f);
+  while (s->next != OOO_SEGMENT_INVALID_INDEX)
+    s = pool_elt_at_index (f->ooo_segments, s->next);
+  return s;
+}
+
 void
 svm_fifo_init (svm_fifo_t * f, u32 size)
 {
@@ -434,8 +448,63 @@ svm_fifo_chunk_alloc (u32 size)
   return c;
 }
 
+static inline u8
+svm_fifo_chunk_includes_pos (svm_fifo_chunk_t * c, u32 pos)
+{
+  return (pos >= c->start_byte && pos < c->start_byte + c->length);
+}
+
+/**
+ * Find chunk for given byte position
+ *
+ * @param f	fifo
+ * @param pos	normalized position in fifo
+ *
+ * @return chunk that includes given position or 0
+ */
+static svm_fifo_chunk_t *
+svm_fifo_find_chunk (svm_fifo_t * f, u32 pos)
+{
+  rb_tree_t *rt = &f->chunk_lookup;
+  rb_node_t *cur, *prev;
+  svm_fifo_chunk_t *c;
+
+  cur = rb_node (rt, rt->root);
+  while (pos != cur->key)
+    {
+      prev = cur;
+      if (pos < cur->key)
+	cur = rb_node_left (rt, cur);
+      else
+	cur = rb_node_right (rt, cur);
+
+      if (rb_node_is_tnil (rt, cur))
+	{
+	  /* Hit tnil as a left child. Find predecessor */
+	  if (pos < prev->key)
+	    {
+	      cur = rb_tree_predecessor (rt, prev);
+	      c = uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
+	      if (svm_fifo_chunk_includes_pos (c, pos))
+		return c;
+	      return 0;
+	    }
+	  /* Hit tnil as a right child. Check if this is the one */
+	  c = uword_to_pointer (prev->opaque, svm_fifo_chunk_t *);
+	  if (svm_fifo_chunk_includes_pos (c, pos))
+	    return c;
+
+	  return 0;
+	}
+    }
+
+  if (!rb_node_is_tnil (rt, cur))
+    return uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
+  return 0;
+}
+
 static inline void
-svm_fifo_size_update (svm_fifo_t * f, svm_fifo_chunk_t * c)
+svm_fifo_grow (svm_fifo_t * f, svm_fifo_chunk_t * c)
 {
   svm_fifo_chunk_t *prev;
   u32 add_bytes = 0;
@@ -458,13 +527,13 @@ svm_fifo_size_update (svm_fifo_t * f, svm_fifo_chunk_t * c)
 }
 
 static void
-svm_fifo_try_size_update (svm_fifo_t * f, u32 new_head)
+svm_fifo_try_grow (svm_fifo_t * f, u32 new_head)
 {
   if (new_head > f->tail)
     return;
 
-  svm_fifo_size_update (f, f->new_chunks);
-  f->flags &= ~SVM_FIFO_F_SIZE_UPDATE;
+  svm_fifo_grow (f, f->new_chunks);
+  f->flags &= ~SVM_FIFO_F_GROW;
 }
 
 void
@@ -472,7 +541,8 @@ svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c)
 {
   svm_fifo_chunk_t *cur, *prev;
 
-  /* Initialize rbtree if needed and add default chunk to it */
+  /* Initialize rbtree if needed and add default chunk to it. Expectation is
+   * that this is called with the heap where the rbtree's pool is pushed. */
   if (!(f->flags & SVM_FIFO_F_MULTI_CHUNK))
     {
       rb_tree_init (&f->chunk_lookup);
@@ -480,8 +550,7 @@ svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c)
       f->flags |= SVM_FIFO_F_MULTI_CHUNK;
     }
 
-  /* Initialize chunks and add to lookup rbtree. Expectation is that this is
-   * called with the heap where the rbtree's pool is pushed. */
+  /* Initialize chunks and add to lookup rbtree */
   cur = c;
   if (f->new_chunks)
     {
@@ -506,7 +575,7 @@ svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c)
   if (!svm_fifo_is_wrapped (f))
     {
       ASSERT (!f->new_chunks);
-      svm_fifo_size_update (f, c);
+      svm_fifo_grow (f, c);
       return;
     }
 
@@ -514,63 +583,129 @@ svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c)
   if (!f->new_chunks)
     {
       f->new_chunks = c;
-      f->flags |= SVM_FIFO_F_SIZE_UPDATE;
+      f->flags |= SVM_FIFO_F_GROW;
     }
 }
 
-static inline u8
-svm_fifo_chunk_includes_pos (svm_fifo_chunk_t * c, u32 pos)
+/**
+ * Removes chunks that are after fifo end byte
+ */
+svm_fifo_chunk_t *
+svm_fifo_collect_chunks (svm_fifo_t * f)
 {
-  return (pos >= c->start_byte && pos < c->start_byte + c->length);
+  svm_fifo_chunk_t *list, *cur;
+
+  f->flags &= ~SVM_FIFO_F_COLLECT_CHUNKS;
+
+  list = f->new_chunks;
+  f->new_chunks = 0;
+  cur = list;
+  while (cur)
+    {
+      rb_tree_del (&f->chunk_lookup, cur->start_byte);
+      cur = cur->next;
+    }
+
+  return list;
+}
+
+void
+svm_fifo_try_shrink (svm_fifo_t * f, u32 head, u32 tail)
+{
+  u32 len_to_shrink = 0, tail_pos, len;
+  svm_fifo_chunk_t *cur, *prev, *next, *start;
+
+  tail_pos = tail;
+  if (f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX)
+    {
+      ooo_segment_t *last = ooo_segment_last (f);
+      tail_pos = ooo_segment_end_pos (f, last);
+    }
+
+  if (f->size_decrement)
+    {
+      /* Figure out available free space considering that there may be
+       * ooo segments */
+      len = clib_min (f->size_decrement, f_free_count (f, head, tail_pos));
+      f->nitems -= len;
+      f->size_decrement -= len;
+    }
+
+  /* Remove tail chunks if the following hold:
+   * - not wrapped
+   * - last used byte less than start of last chunk
+   */
+  if (tail_pos >= head && tail_pos <= f->end_chunk->start_byte)
+    {
+      /* Lookup the last position not to be removed. Since size still needs
+       * to be nitems + 1, nitems must fall within the usable space */
+      tail_pos = tail_pos > 0 ? tail_pos - 1 : tail_pos;
+      prev = svm_fifo_find_chunk (f, clib_max (f->nitems, tail_pos));
+      next = prev->next;
+      while (next != f->start_chunk)
+	{
+	  cur = next;
+	  next = cur->next;
+	  len_to_shrink += cur->length;
+	}
+      if (len_to_shrink)
+	{
+	  f->size -= len_to_shrink;
+	  start = prev->next;
+	  prev->next = f->start_chunk;
+	  f->end_chunk = prev;
+	  cur->next = f->new_chunks;
+	  f->new_chunks = start;
+	}
+    }
+
+  if (!f->size_decrement && f->size == f->nitems + 1)
+    {
+      f->flags &= ~SVM_FIFO_F_SHRINK;
+      f->flags |= SVM_FIFO_F_COLLECT_CHUNKS;
+      if (f->start_chunk == f->start_chunk->next)
+	f->flags &= ~SVM_FIFO_F_MULTI_CHUNK;
+    }
 }
 
 /**
- * Find chunk for given byte position
- *
- * @param f	fifo
- * @param pos	normalized position in fifo
- *
- * @return chunk that includes given position or 0
+ * Request to reduce fifo size by amount of bytes
  */
-static svm_fifo_chunk_t *
-svm_fifo_find_chunk (svm_fifo_t * f, u32 pos)
+int
+svm_fifo_reduce_size (svm_fifo_t * f, u32 len, u8 try_shrink)
 {
-  rb_tree_t *rt = &f->chunk_lookup;
-  rb_node_t *cur, *prev;
-  svm_fifo_chunk_t *c;
+  svm_fifo_chunk_t *cur;
+  u32 actual_len = 0;
 
-  cur = rb_node (rt, rt->root);
-  while (pos != cur->key)
+  if (len > f->nitems)
+    return 0;
+
+  /* last chunk that will not be removed */
+  cur = svm_fifo_find_chunk (f, f->nitems - len);
+
+  /* sum length of chunks that will be removed */
+  cur = cur->next;
+  while (cur != f->start_chunk)
     {
-      prev = cur;
-      if (pos < cur->key)
-	cur = rb_node_left (rt, cur);
-      else
-	cur = rb_node_right (rt, cur);
+      actual_len += cur->length;
+      cur = cur->next;
+    }
 
-      if (rb_node_is_tnil (rt, cur))
-	{
-	  /* Hit tnil as a left child. Find predecessor */
-	  if (pos < prev->key)
-	    {
-	      cur = rb_tree_predecessor (rt, prev);
-	      c = uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
-	      if (svm_fifo_chunk_includes_pos (c, pos))
-		return c;
-	      return 0;
-	    }
-	  /* Hit tnil as a right child. Check if this is the one */
-	  c = uword_to_pointer (prev->opaque, svm_fifo_chunk_t *);
-	  if (svm_fifo_chunk_includes_pos (c, pos))
-	    return c;
+  ASSERT (actual_len <= len);
+  if (!actual_len)
+    return 0;
 
-	  return 0;
-	}
+  f->size_decrement = actual_len;
+  f->flags |= SVM_FIFO_F_SHRINK;
+
+  if (try_shrink)
+    {
+      u32 head, tail;
+      f_load_head_tail_prod (f, &head, &tail);
+      svm_fifo_try_shrink (f, head, tail);
     }
 
-  if (!rb_node_is_tnil (rt, cur))
-    return uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
-  return 0;
+  return actual_len;
 }
 
 void
@@ -660,6 +795,9 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
 
   f_load_head_tail_prod (f, &head, &tail);
 
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SHRINK))
+    svm_fifo_try_shrink (f, head, tail);
+
   /* free space in fifo can only increase during enqueue: SPSC */
   free_count = f_free_count (f, head, tail);
 
@@ -680,6 +818,22 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
   return 0;
 }
 
+/**
+ * Advance tail
+ */
+void
+svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len)
+{
+  u32 tail;
+
+  ASSERT (len <= svm_fifo_max_enqueue_prod (f));
+  /* load-relaxed: producer owned index */
+  tail = f->tail;
+  tail = (tail + len) % f->size;
+  /* store-rel: producer owned index (paired with load-acq in consumer) */
+  clib_atomic_store_rel_n (&f->tail, tail);
+}
+
 int
 svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst)
 {
@@ -697,8 +851,8 @@ svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst)
   svm_fifo_copy_from_chunk (f, f->head_chunk, head, dst, len, &f->head_chunk);
   head = (head + len) % f->size;
 
-  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SIZE_UPDATE))
-    svm_fifo_try_size_update (f, head);
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_GROW))
+    svm_fifo_try_grow (f, head);
 
   /* store-rel: consumer owned index (paired with load-acq in producer) */
   clib_atomic_store_rel_n (&f->head, head);
diff --git a/src/svm/svm_fifo.h b/src/svm/svm_fifo.h
index 390e1170e27..417b0ecb672 100644
--- a/src/svm/svm_fifo.h
+++ b/src/svm/svm_fifo.h
@@ -64,9 +64,11 @@ typedef struct svm_fifo_chunk_
 
 typedef enum svm_fifo_flag_
 {
-  SVM_FIFO_F_SIZE_UPDATE = 1 << 0,
-  SVM_FIFO_F_MULTI_CHUNK = 1 << 1,
-  SVM_FIFO_F_LL_TRACKED = 1 << 2,
+  SVM_FIFO_F_MULTI_CHUNK = 1 << 0,
+  SVM_FIFO_F_GROW = 1 << 1,
+  SVM_FIFO_F_SHRINK = 1 << 2,
+  SVM_FIFO_F_COLLECT_CHUNKS = 1 << 3,
+  SVM_FIFO_F_LL_TRACKED = 1 << 4,
 } svm_fifo_flag_t;
 
 typedef struct _svm_fifo
@@ -86,12 +88,13 @@ typedef struct _svm_fifo
   u32 client_session_index;	/**< app session index */
   u8 master_thread_index;	/**< session layer thread index */
   u8 client_thread_index;	/**< app worker index */
+  i8 refcnt;			/**< reference count  */
   u32 segment_manager;		/**< session layer segment manager index */
   u32 segment_index;		/**< segment index in segment manager */
   u32 freelist_index;		/**< aka log2(allocated_size) - const. */
-  i8 refcnt;			/**< reference count  */
   struct _svm_fifo *next;	/**< next in freelist/active chain */
   struct _svm_fifo *prev;	/**< prev in active chain */
+  u32 size_decrement;		/**< bytes to remove from fifo */
 
     CLIB_CACHE_LINE_ALIGN_MARK (consumer);
   u32 head;			/**< fifo head position/byte */
@@ -172,7 +175,8 @@ f_load_head_tail_prod (svm_fifo_t * f, u32 * head, u32 * tail)
   *head = clib_atomic_load_acq_n (&f->head);
 }
 
-/* Load head and tail independent of producer/consumer role
+/**
+ * Load head and tail independent of producer/consumer role
  *
  * Internal function.
  */
@@ -230,6 +234,13 @@ f_free_count (svm_fifo_t * f, u32 head, u32 tail)
 }
 
 /**
+ * Try to shrink fifo size.
+ *
+ * Internal function.
+ */
+void svm_fifo_try_shrink (svm_fifo_t * f, u32 head, u32 tail);
+
+/**
  * Create fifo of requested size
  *
  * Allocates fifo on current heap.
@@ -267,6 +278,31 @@ svm_fifo_chunk_t *svm_fifo_chunk_alloc (u32 size);
  */
 void svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c);
 /**
+ * Request to reduce fifo size by amount of bytes
+ *
+ * Because the producer might be enqueuing data when this is called, the
+ * actual size update is only applied when producer tries to enqueue new
+ * data, unless @param try_shrink is set.
+ *
+ * @param f		fifo
+ * @param len		number of bytes to remove from fifo. The actual number
+ * 			of bytes to be removed will be less or equal to this
+ * 			value.
+ * @param try_shrink	flg to indicate if it's safe to try to shrink fifo
+ * 			size. It should be set only if this is called by the
+ * 			producer of if the producer is not using the fifo
+ * @return		actual length fifo size will be reduced by
+ */
+int svm_fifo_reduce_size (svm_fifo_t * f, u32 len, u8 try_shrink);
+/**
+ * Removes chunks that are after fifo end byte
+ *
+ * Needs to be called with segment heap pushed.
+ *
+ * @param f fifo
+ */
+svm_fifo_chunk_t *svm_fifo_collect_chunks (svm_fifo_t * f);
+/**
  * Free fifo and associated state
  *
  * @param f	fifo
@@ -333,6 +369,16 @@ int svm_fifo_enqueue (svm_fifo_t * f, u32 len, const u8 * src);
  */
 int svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len,
 				  u8 * src);
+
+/**
+ * Advance tail pointer
+ *
+ * Useful for moving tail pointer after external enqueue.
+ *
+ * @param f		fifo
+ * @param len		number of bytes to add to tail
+ */
+void svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len);
 /**
  * Overwrite fifo head with new data
  *
@@ -551,6 +597,8 @@ svm_fifo_max_enqueue_prod (svm_fifo_t * f)
 {
   u32 head, tail;
   f_load_head_tail_prod (f, &head, &tail);
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SHRINK))
+    svm_fifo_try_shrink (f, head, tail);
   return f_free_count (f, head, tail);
 }
 
@@ -565,6 +613,8 @@ svm_fifo_max_enqueue (svm_fifo_t * f)
 {
   u32 head, tail;
   f_load_head_tail_all_acq (f, &head, &tail);
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SHRINK))
+    svm_fifo_try_shrink (f, head, tail);
   return f_free_count (f, head, tail);
 }
 
@@ -590,25 +640,6 @@ svm_fifo_max_write_chunk (svm_fifo_t * f)
   return tail > head ? f->size - tail : f_free_count (f, head, tail);
 }
 
-/**
- * Advance tail pointer
- *
- * Useful for moving tail pointer after external enqueue.
- *
- * @param f		fifo
- * @param len		number of bytes to add to tail
- */
-static inline void
-svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len)
-{
-  ASSERT (len <= svm_fifo_max_enqueue_prod (f));
-  /* load-relaxed: producer owned index */
-  u32 tail = f->tail;
-  tail = (tail + len) % f->size;
-  /* store-rel: producer owned index (paired with load-acq in consumer) */
-  clib_atomic_store_rel_n (&f->tail, tail);
-}
-
 static inline u8 *
 svm_fifo_head (svm_fifo_t * f)
 {