session: segment manager refactor

- use valloc as a 'central' segment baseva manager
- use per segment manager segment pools and use rwlocks to guard them
- add session test that exercises segment creation
- embed segment manager properties into application since they're shared
- fix rw locks

Change-Id: I761164c147275d9e8a926f1eda395e090d231f9a
Signed-off-by: Florin Coras <fcoras@cisco.com>

21 files changed, 878 insertions, 620 deletions

diff --git a/src/svm/ssvm.c b/src/svm/ssvm.c
index 50552198137..7077f8be641 100644
--- a/src/svm/ssvm.c
+++ b/src/svm/ssvm.c
@@ -19,11 +19,11 @@ typedef int (*init_fn) (ssvm_private_t *);
 typedef void (*delete_fn) (ssvm_private_t *);
 
 static init_fn master_init_fns[SSVM_N_SEGMENT_TYPES] =
-  { ssvm_master_init_shm, ssvm_master_init_memfd };
+  { ssvm_master_init_shm, ssvm_master_init_memfd, ssvm_master_init_private };
 static init_fn slave_init_fns[SSVM_N_SEGMENT_TYPES] =
-  { ssvm_slave_init_shm, ssvm_slave_init_memfd };
+  { ssvm_slave_init_shm, ssvm_slave_init_memfd, ssvm_slave_init_private };
 static delete_fn delete_fns[SSVM_N_SEGMENT_TYPES] =
-  { ssvm_delete_shm, ssvm_delete_memfd };
+  { ssvm_delete_shm, ssvm_delete_memfd, ssvm_delete_private };
 
 int
 ssvm_master_init_shm (ssvm_private_t * ssvm)
@@ -315,6 +315,59 @@ ssvm_delete_memfd (ssvm_private_t * memfd)
   close (memfd->fd);
 }
 
+/**
+ * Initialize segment in a private heap
+ */
+int
+ssvm_master_init_private (ssvm_private_t * ssvm)
+{
+  u32 pagesize = clib_mem_get_page_size ();
+  ssvm_shared_header_t *sh;
+  mheap_t *heap_header;
+  u32 rnd_size = 0;
+  u8 *heap;
+
+  rnd_size = (ssvm->ssvm_size + (pagesize - 1)) & ~pagesize;
+  heap = mheap_alloc (0, rnd_size);
+  if (heap == 0)
+    {
+      clib_unix_warning ("mheap alloc");
+      return -1;
+    }
+  heap_header = mheap_header (heap);
+  heap_header->flags |= MHEAP_FLAG_THREAD_SAFE;
+
+  ssvm->ssvm_size = rnd_size;
+  ssvm->i_am_master = 1;
+  ssvm->my_pid = getpid ();
+  ssvm->requested_va = ~0;
+
+  /* Allocate a [sic] shared memory header, in process memory... */
+  sh = clib_mem_alloc_aligned (sizeof (*sh), CLIB_CACHE_LINE_BYTES);
+  ssvm->sh = sh;
+
+  memset (sh, 0, sizeof (*sh));
+  sh->heap = heap;
+  sh->type = SSVM_SEGMENT_PRIVATE;
+
+  return 0;
+}
+
+int
+ssvm_slave_init_private (ssvm_private_t * ssvm)
+{
+  clib_warning ("BUG: this should not be called!");
+  return -1;
+}
+
+void
+ssvm_delete_private (ssvm_private_t * ssvm)
+{
+  vec_free (ssvm->name);
+  mheap_free (ssvm->sh->heap);
+  clib_mem_free (ssvm->sh);
+}
+
 int
 ssvm_master_init (ssvm_private_t * ssvm, ssvm_segment_type_t type)
 {
diff --git a/src/svm/ssvm.h b/src/svm/ssvm.h
index 9bf009e73d2..09e1707450b 100644
--- a/src/svm/ssvm.h
+++ b/src/svm/ssvm.h
@@ -49,6 +49,7 @@ typedef enum ssvm_segment_type_
 {
   SSVM_SEGMENT_SHM = 0,
   SSVM_SEGMENT_MEMFD,
+  SSVM_SEGMENT_PRIVATE,
   SSVM_N_SEGMENT_TYPES		/**< Private segments */
 } ssvm_segment_type_t;
 
@@ -195,6 +196,10 @@ int ssvm_master_init_memfd (ssvm_private_t * memfd);
 int ssvm_slave_init_memfd (ssvm_private_t * memfd);
 void ssvm_delete_memfd (ssvm_private_t * memfd);
 
+int ssvm_master_init_private (ssvm_private_t * ssvm);
+int ssvm_slave_init_private (ssvm_private_t * ssvm);
+void ssvm_delete_private (ssvm_private_t * ssvm);
+
 ssvm_segment_type_t ssvm_type (const ssvm_private_t * ssvm);
 u8 *ssvm_name (const ssvm_private_t * ssvm);
 
diff --git a/src/svm/svm_fifo_segment.c b/src/svm/svm_fifo_segment.c
index 4d1833eee7e..459b1d1d8e5 100644
--- a/src/svm/svm_fifo_segment.c
+++ b/src/svm/svm_fifo_segment.c
@@ -56,69 +56,75 @@ allocate_new_fifo_chunk (svm_fifo_segment_header_t * fsh,
     }
 }
 
-static void
-preallocate_fifo_pairs (svm_fifo_segment_private_t * s,
-			svm_fifo_segment_create_args_t * a, u32 protect_size)
+/**
+ * Pre-allocates fifo pairs in fifo segment
+ *
+ * The number of fifos pre-allocated is the minimum of the requested number
+ * of pairs and the maximum number that fit within the segment. If the maximum
+ * is hit, the number of fifo pairs requested is updated by subtracting the
+ * number of fifos that have been successfully allocated.
+ */
+void
+svm_fifo_segment_preallocate_fifo_pairs (svm_fifo_segment_private_t * s,
+					 u32 rx_fifo_size, u32 tx_fifo_size,
+					 u32 * n_fifo_pairs)
 {
-  svm_fifo_segment_header_t *fsh = s->h;
-  u32 rx_fifo_size, tx_fifo_size, pairs_to_allocate;
   u32 rx_rounded_data_size, tx_rounded_data_size, pair_size;
-  svm_fifo_t *f;
-  u8 *rx_fifo_space, *tx_fifo_space;
+  u32 rx_fifos_size, tx_fifos_size, pairs_to_allocate;
   int rx_freelist_index, tx_freelist_index;
+  ssvm_shared_header_t *sh = s->ssvm.sh;
+  svm_fifo_segment_header_t *fsh = s->h;
+  u8 *rx_fifo_space, *tx_fifo_space;
+  uword space_available;
+  void *oldheap;
+  svm_fifo_t *f;
   int i;
 
   /* Parameter check */
-  if (a->rx_fifo_size == 0 || a->tx_fifo_size == 0
-      || a->preallocated_fifo_pairs == 0)
+  if (rx_fifo_size == 0 || tx_fifo_size == 0 || *n_fifo_pairs == 0)
     return;
 
-  if (a->rx_fifo_size < FIFO_SEGMENT_MIN_FIFO_SIZE ||
-      a->rx_fifo_size > FIFO_SEGMENT_MAX_FIFO_SIZE)
+  if (rx_fifo_size < FIFO_SEGMENT_MIN_FIFO_SIZE ||
+      rx_fifo_size > FIFO_SEGMENT_MAX_FIFO_SIZE)
     {
-      clib_warning ("rx fifo_size out of range %d", a->rx_fifo_size);
+      clib_warning ("rx fifo_size out of range %d", rx_fifo_size);
       return;
     }
 
-  if (a->tx_fifo_size < FIFO_SEGMENT_MIN_FIFO_SIZE ||
-      a->tx_fifo_size > FIFO_SEGMENT_MAX_FIFO_SIZE)
+  if (tx_fifo_size < FIFO_SEGMENT_MIN_FIFO_SIZE ||
+      tx_fifo_size > FIFO_SEGMENT_MAX_FIFO_SIZE)
     {
-      clib_warning ("tx fifo_size out of range %d", a->rx_fifo_size);
+      clib_warning ("tx fifo_size out of range %d", rx_fifo_size);
       return;
     }
 
-  rx_rounded_data_size = (1 << (max_log2 (a->rx_fifo_size)));
-
-  rx_freelist_index = max_log2 (a->rx_fifo_size)
+  rx_rounded_data_size = (1 << (max_log2 (rx_fifo_size)));
+  rx_freelist_index = max_log2 (rx_fifo_size)
     - max_log2 (FIFO_SEGMENT_MIN_FIFO_SIZE);
-
-  tx_rounded_data_size = (1 << (max_log2 (a->rx_fifo_size)));
-
-  tx_freelist_index = max_log2 (a->tx_fifo_size)
+  tx_rounded_data_size = (1 << (max_log2 (tx_fifo_size)));
+  tx_freelist_index = max_log2 (tx_fifo_size)
     - max_log2 (FIFO_SEGMENT_MIN_FIFO_SIZE);
 
   /* Calculate space requirements */
   pair_size = 2 * sizeof (*f) + rx_rounded_data_size + tx_rounded_data_size;
-  if (protect_size)
-    protect_size += mheap_bytes (s->ssvm.sh->heap);
-  pairs_to_allocate =
-    clib_min ((s->ssvm.ssvm_size - protect_size) / pair_size,
-	      a->preallocated_fifo_pairs);
-  rx_fifo_size = (sizeof (*f) + rx_rounded_data_size) * pairs_to_allocate;
-  tx_fifo_size = (sizeof (*f) + tx_rounded_data_size) * pairs_to_allocate;
+  space_available = s->ssvm.ssvm_size - mheap_bytes (sh->heap);
+  pairs_to_allocate = clib_min (space_available / pair_size, *n_fifo_pairs);
+  rx_fifos_size = (sizeof (*f) + rx_rounded_data_size) * pairs_to_allocate;
+  tx_fifos_size = (sizeof (*f) + tx_rounded_data_size) * pairs_to_allocate;
 
   vec_validate_init_empty (fsh->free_fifos,
 			   clib_max (rx_freelist_index, tx_freelist_index),
 			   0);
 
+  oldheap = ssvm_push_heap (sh);
   /* Allocate rx fifo space. May fail. */
   rx_fifo_space = clib_mem_alloc_aligned_at_offset
-    (rx_fifo_size, CLIB_CACHE_LINE_BYTES, 0 /* align_offset */ ,
+    (rx_fifos_size, CLIB_CACHE_LINE_BYTES, 0 /* align_offset */ ,
      0 /* os_out_of_memory */ );
 
   /* Same for TX */
   tx_fifo_space = clib_mem_alloc_aligned_at_offset
-    (tx_fifo_size, CLIB_CACHE_LINE_BYTES, 0 /* align_offset */ ,
+    (tx_fifos_size, CLIB_CACHE_LINE_BYTES, 0 /* align_offset */ ,
      0 /* os_out_of_memory */ );
 
   /* Make sure it worked. Clean up if it didn't... */
@@ -128,13 +134,14 @@ preallocate_fifo_pairs (svm_fifo_segment_private_t * s,
 	clib_mem_free (rx_fifo_space);
       else
 	clib_warning ("rx fifo preallocation failure: size %d npairs %d",
-		      a->rx_fifo_size, a->preallocated_fifo_pairs);
+		      rx_fifo_size, *n_fifo_pairs);
 
       if (tx_fifo_space)
 	clib_mem_free (tx_fifo_space);
       else
 	clib_warning ("tx fifo preallocation failure: size %d nfifos %d",
-		      a->tx_fifo_size, a->preallocated_fifo_pairs);
+		      tx_fifo_size, *n_fifo_pairs);
+      ssvm_pop_heap (oldheap);
       return;
     }
 
@@ -160,7 +167,31 @@ preallocate_fifo_pairs (svm_fifo_segment_private_t * s,
     }
 
   /* Account for the pairs allocated */
-  a->preallocated_fifo_pairs -= pairs_to_allocate;
+  *n_fifo_pairs -= pairs_to_allocate;
+  ssvm_pop_heap (oldheap);
+}
+
+/**
+ * Initialize svm fifo segment shared header
+ */
+int
+svm_fifo_segment_init (svm_fifo_segment_private_t * s)
+{
+  svm_fifo_segment_header_t *fsh;
+  ssvm_shared_header_t *sh;
+  void *oldheap;
+
+  sh = s->ssvm.sh;
+  oldheap = ssvm_push_heap (sh);
+
+  fsh = clib_mem_alloc (sizeof (*fsh));
+  memset (fsh, 0, sizeof (*fsh));
+  s->h = sh->opaque[0] = fsh;
+
+  ssvm_pop_heap (oldheap);
+
+  sh->ready = 1;
+  return (0);
 }
 
 /**
@@ -171,9 +202,6 @@ svm_fifo_segment_create (svm_fifo_segment_create_args_t * a)
 {
   svm_fifo_segment_main_t *sm = &svm_fifo_segment_main;
   svm_fifo_segment_private_t *s;
-  ssvm_shared_header_t *sh;
-  svm_fifo_segment_header_t *fsh;
-  void *oldheap;
   int rv;
 
   /* Allocate a fresh segment */
@@ -195,18 +223,7 @@ svm_fifo_segment_create (svm_fifo_segment_create_args_t * a)
   /* Note: requested_va updated due to seg base addr randomization */
   sm->next_baseva = s->ssvm.sh->ssvm_va + a->segment_size;
 
-  sh = s->ssvm.sh;
-  oldheap = ssvm_push_heap (sh);
-
-  /* Set up svm_fifo_segment shared header */
-  fsh = clib_mem_alloc (sizeof (*fsh));
-  memset (fsh, 0, sizeof (*fsh));
-  s->h = sh->opaque[0] = fsh;
-  preallocate_fifo_pairs (s, a, a->seg_protected_space);
-
-  ssvm_pop_heap (oldheap);
-
-  sh->ready = 1;
+  svm_fifo_segment_init (s);
   vec_add1 (a->new_segment_indices, s - sm->segments);
   return (0);
 }
@@ -217,78 +234,45 @@ svm_fifo_segment_create (svm_fifo_segment_create_args_t * a)
 int
 svm_fifo_segment_create_process_private (svm_fifo_segment_create_args_t * a)
 {
-  svm_fifo_segment_private_t *s;
   svm_fifo_segment_main_t *sm = &svm_fifo_segment_main;
+  svm_fifo_segment_private_t *s;
   ssvm_shared_header_t *sh;
-  svm_fifo_segment_header_t *fsh;
-  void *oldheap;
-  u8 **heaps = 0;
   mheap_t *heap_header;
-  int segment_count = 1;
   u32 rnd_size = 0;
-  int i;
+  u8 *heap;
+  u32 pagesize = clib_mem_get_page_size ();
 
-  if (a->private_segment_count)
-    {
-      u8 *heap;
-      u32 pagesize = clib_mem_get_page_size ();
-      rnd_size = (a->segment_size + (pagesize - 1)) & ~pagesize;
+  pool_get (sm->segments, s);
+  memset (s, 0, sizeof (*s));
 
-      for (i = 0; i < a->private_segment_count; i++)
-	{
-	  heap = mheap_alloc (0, rnd_size);
-	  if (heap == 0)
-	    {
-	      clib_unix_warning ("mheap alloc");
-	      return -1;
-	    }
-	  heap_header = mheap_header (heap);
-	  heap_header->flags |= MHEAP_FLAG_THREAD_SAFE;
-	  vec_add1 (heaps, heap);
-	}
-      segment_count = a->private_segment_count;
-    }
+  rnd_size = (a->segment_size + (pagesize - 1)) & ~pagesize;
 
-  /* Allocate segments */
-  for (i = 0; i < segment_count; i++)
+  heap = mheap_alloc (0, rnd_size);
+  if (heap == 0)
     {
-      pool_get (sm->segments, s);
-      memset (s, 0, sizeof (*s));
-
-      s->ssvm.ssvm_size = rnd_size;
-      s->ssvm.i_am_master = 1;
-      s->ssvm.my_pid = getpid ();
-      s->ssvm.name = format (0, "%s%c", a->segment_name, 0);
-      s->ssvm.requested_va = ~0;
-
-      /* Allocate a [sic] shared memory header, in process memory... */
-      sh = clib_mem_alloc_aligned (sizeof (*sh), CLIB_CACHE_LINE_BYTES);
-      s->ssvm.sh = sh;
-
-      memset (sh, 0, sizeof (*sh));
-      sh->heap = a->private_segment_count ? heaps[i] : clib_mem_get_heap ();
-
-      /* Set up svm_fifo_segment shared header */
-      fsh = clib_mem_alloc (sizeof (*fsh));
-      memset (fsh, 0, sizeof (*fsh));
-      fsh->flags = FIFO_SEGMENT_F_IS_PRIVATE;
-      s->h = sh->opaque[0] = fsh;
-      if (!a->private_segment_count)
-	fsh->flags |= FIFO_SEGMENT_F_IS_MAIN_HEAP;
-
-      if (a->private_segment_count)
-	{
-	  if (i != 0)
-	    fsh->flags |= FIFO_SEGMENT_F_IS_PREALLOCATED;
-	  oldheap = clib_mem_get_heap ();
-	  clib_mem_set_heap (sh->heap);
-	  preallocate_fifo_pairs (s, a, i == 0 ? a->seg_protected_space : 0);
-	  clib_mem_set_heap (oldheap);
-	}
-      sh->ready = 1;
-      vec_add1 (a->new_segment_indices, s - sm->segments);
+      clib_unix_warning ("mheap alloc");
+      pool_put (sm->segments, s);
+      return -1;
     }
-  vec_free (heaps);
+  heap_header = mheap_header (heap);
+  heap_header->flags |= MHEAP_FLAG_THREAD_SAFE;
+
+  s->ssvm.ssvm_size = rnd_size;
+  s->ssvm.i_am_master = 1;
+  s->ssvm.my_pid = getpid ();
+  s->ssvm.name = format (0, "%s%c", a->segment_name, 0);
+  s->ssvm.requested_va = ~0;
+
+  /* Allocate a [sic] shared memory header, in process memory... */
+  sh = clib_mem_alloc_aligned (sizeof (*sh), CLIB_CACHE_LINE_BYTES);
+  s->ssvm.sh = sh;
+
+  memset (sh, 0, sizeof (*sh));
+  sh->heap = heap;
+
+  svm_fifo_segment_init (s);
+  vec_add1 (a->new_segment_indices, s - sm->segments);
+
   return (0);
 }
 
@@ -333,18 +317,7 @@ svm_fifo_segment_delete (svm_fifo_segment_private_t * s)
 {
   svm_fifo_segment_main_t *sm = &svm_fifo_segment_main;
 
-  if (s->h->flags & FIFO_SEGMENT_F_IS_PRIVATE)
-    {
-      /* Don't try to free vpp's heap! */
-      if (!(s->h->flags & FIFO_SEGMENT_F_IS_MAIN_HEAP))
-	mheap_free (s->ssvm.sh->heap);
-      clib_mem_free (s->ssvm.sh);
-      clib_mem_free (s->h);
-    }
-  else
-    {
-      ssvm_delete (&s->ssvm);
-    }
+  ssvm_delete (&s->ssvm);
   memset (s, 0xfe, sizeof (*s));
   pool_put (sm->segments, s);
 }
@@ -378,10 +351,10 @@ svm_fifo_segment_alloc_fifo (svm_fifo_segment_private_t * s,
     - max_log2 (FIFO_SEGMENT_MIN_FIFO_SIZE);
 
   sh = s->ssvm.sh;
-  fsh = (svm_fifo_segment_header_t *) sh->opaque[0];
 
   ssvm_lock_non_recursive (sh, 1);
   oldheap = ssvm_push_heap (sh);
+  fsh = (svm_fifo_segment_header_t *) sh->opaque[0];
 
   switch (list_index)
     {
@@ -508,7 +481,7 @@ svm_fifo_segment_free_fifo (svm_fifo_segment_private_t * s, svm_fifo_t * f,
 }
 
 void
-svm_fifo_segment_init (u64 baseva, u32 timeout_in_seconds)
+svm_fifo_segment_main_init (u64 baseva, u32 timeout_in_seconds)
 {
   svm_fifo_segment_main_t *sm = &svm_fifo_segment_main;
 
@@ -595,7 +568,7 @@ void
 svm_fifo_segment_info (svm_fifo_segment_private_t * seg, uword * address,
 		       u64 * size)
 {
-  if (seg->h->flags & FIFO_SEGMENT_F_IS_PRIVATE)
+  if (ssvm_type (&seg->ssvm) == SSVM_SEGMENT_PRIVATE)
     {
       mheap_t *heap_header;
 
@@ -623,12 +596,8 @@ format_svm_fifo_segment_type (u8 * s, va_list * args)
   sp = va_arg (*args, svm_fifo_segment_private_t *);
   ssvm_segment_type_t st = ssvm_type (&sp->ssvm);
 
-  if ((sp->h->flags & FIFO_SEGMENT_F_IS_PRIVATE)
-      && !(sp->h->flags & FIFO_SEGMENT_F_IS_MAIN_HEAP))
+  if (st == SSVM_SEGMENT_PRIVATE)
     s = format (s, "%s", "private-heap");
-  else if ((sp->h->flags & FIFO_SEGMENT_F_IS_PRIVATE)
-	   && (sp->h->flags & FIFO_SEGMENT_F_IS_MAIN_HEAP))
-    s = format (s, "%s", "main-heap");
   else if (st == SSVM_SEGMENT_MEMFD)
     s = format (s, "%s", "memfd");
   else if (st == SSVM_SEGMENT_SHM)
diff --git a/src/svm/svm_fifo_segment.h b/src/svm/svm_fifo_segment.h
index 0e86c25deab..bf8d5139e3c 100644
--- a/src/svm/svm_fifo_segment.h
+++ b/src/svm/svm_fifo_segment.h
@@ -31,10 +31,8 @@ typedef enum
 #define FIFO_SEGMENT_MAX_FIFO_SIZE (8<<20)	/* 8mb max fifo size */
 #define FIFO_SEGMENT_ALLOC_CHUNK_SIZE 32	/* Allocation quantum */
 
-#define FIFO_SEGMENT_F_IS_PRIVATE 	1 << 0	/* Private segment */
-#define FIFO_SEGMENT_F_IS_MAIN_HEAP	1 << 1	/* Segment is main heap */
-#define FIFO_SEGMENT_F_IS_PREALLOCATED	1 << 2	/* Segment is preallocated */
-#define FIFO_SEGMENT_F_WILL_DELETE	1 << 3	/* Segment will be removed */
+#define FIFO_SEGMENT_F_IS_PREALLOCATED	1 << 0	/* Segment is preallocated */
+#define FIFO_SEGMENT_F_WILL_DELETE	1 << 1	/* Segment will be removed */
 
 typedef struct
 {
@@ -69,14 +67,11 @@ typedef struct
   char *segment_name;
   u32 segment_size;
   u32 *new_segment_indices;
-  u32 rx_fifo_size;
-  u32 tx_fifo_size;
-  u32 preallocated_fifo_pairs;
-  u32 private_segment_count;
-  u32 seg_protected_space;
   int memfd_fd;
 } svm_fifo_segment_create_args_t;
 
+#define svm_fifo_segment_flags(_seg) _seg->h->flags
+
 static inline svm_fifo_segment_private_t *
 svm_fifo_segment_get_segment (u32 segment_index)
 {
@@ -96,19 +91,14 @@ svm_fifo_segment_get_fifo_list (svm_fifo_segment_private_t * fifo_segment)
   return fifo_segment->h->fifos;
 }
 
-#define foreach_ssvm_fifo_segment_api_error             \
-_(OUT_OF_SPACE, "Out of space in segment", -200)
-
-typedef enum
-{
-#define _(n,s,c) SSVM_FIFO_SEGMENT_API_ERROR_##n = c,
-  foreach_ssvm_fifo_segment_api_error
-#undef _
-} ssvm_fifo_segment_api_error_enum_t;
-
+int svm_fifo_segment_init (svm_fifo_segment_private_t * s);
 int svm_fifo_segment_create (svm_fifo_segment_create_args_t * a);
 int svm_fifo_segment_create_process_private (svm_fifo_segment_create_args_t
 					     * a);
+void svm_fifo_segment_preallocate_fifo_pairs (svm_fifo_segment_private_t * s,
+					      u32 rx_fifo_size,
+					      u32 tx_fifo_size,
+					      u32 * n_fifo_pairs);
 int svm_fifo_segment_attach (svm_fifo_segment_create_args_t * a);
 void svm_fifo_segment_delete (svm_fifo_segment_private_t * s);
 
@@ -118,7 +108,7 @@ svm_fifo_t *svm_fifo_segment_alloc_fifo (svm_fifo_segment_private_t * s,
 void svm_fifo_segment_free_fifo (svm_fifo_segment_private_t * s,
 				 svm_fifo_t * f,
 				 svm_fifo_segment_freelist_t index);
-void svm_fifo_segment_init (u64 baseva, u32 timeout_in_seconds);
+void svm_fifo_segment_main_init (u64 baseva, u32 timeout_in_seconds);
 u32 svm_fifo_segment_index (svm_fifo_segment_private_t * s);
 u32 svm_fifo_segment_num_fifos (svm_fifo_segment_private_t * fifo_segment);
 u32 svm_fifo_segment_num_free_fifos (svm_fifo_segment_private_t *
diff --git a/src/svm/test_svm_fifo1.c b/src/svm/test_svm_fifo1.c
index 3bdca9499f9..d5b2c98dfc3 100644
--- a/src/svm/test_svm_fifo1.c
+++ b/src/svm/test_svm_fifo1.c
@@ -30,9 +30,6 @@ hello_world (int verbose)
 
   a->segment_name = "fifo-test1";
   a->segment_size = 256 << 10;
-  a->rx_fifo_size = 4096;
-  a->tx_fifo_size = 4096;
-  a->preallocated_fifo_pairs = 4;
 
   rv = svm_fifo_segment_create (a);
 
@@ -276,7 +273,7 @@ test_ssvm_fifo1 (unformat_input_t * input)
   int verbose = 0;
   int test_id = 0;
 
-  svm_fifo_segment_init (0x200000000ULL, 20);
+  svm_fifo_segment_main_init (0x200000000ULL, 20);
 
   while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
     {
diff --git a/src/tests/vnet/session/tcp_echo.c b/src/tests/vnet/session/tcp_echo.c
index a5ad35ae80a..d48c5d9de03 100644
--- a/src/tests/vnet/session/tcp_echo.c
+++ b/src/tests/vnet/session/tcp_echo.c
@@ -1277,7 +1277,7 @@ main (int argc, char **argv)
 
   clib_time_init (&em->clib_time);
   init_error_string_table (em);
-  svm_fifo_segment_init (0x200000000ULL, 20);
+  svm_fifo_segment_main_init (0x200000000ULL, 20);
   unformat_init_command_line (a, argv);
 
   while (unformat_check_input (a) != UNFORMAT_END_OF_INPUT)
diff --git a/src/tests/vnet/session/udp_echo.c b/src/tests/vnet/session/udp_echo.c
index 283895102a2..e425169b944 100644
--- a/src/tests/vnet/session/udp_echo.c
+++ b/src/tests/vnet/session/udp_echo.c
@@ -1071,7 +1071,7 @@ main (int argc, char **argv)
 
   clib_time_init (&utm->clib_time);
   init_error_string_table (utm);
-  svm_fifo_segment_init (0x200000000ULL, 20);
+  svm_fifo_segment_main_init (0x200000000ULL, 20);
   unformat_init_command_line (a, argv);
 
   while (unformat_check_input (a) != UNFORMAT_END_OF_INPUT)
diff --git a/src/vcl/vppcom.c b/src/vcl/vppcom.c
index 167a74591e7..dd7e90e2a99 100644
--- a/src/vcl/vppcom.c
+++ b/src/vcl/vppcom.c
@@ -2304,8 +2304,8 @@ vppcom_app_create (char *app_name)
 
       clib_time_init (&vcm->clib_time);
       vppcom_init_error_string_table ();
-      svm_fifo_segment_init (vcl_cfg->segment_baseva,
-			     20 /* timeout in secs */ );
+      svm_fifo_segment_main_init (vcl_cfg->segment_baseva,
+				  20 /* timeout in secs */ );
       clib_spinlock_init (&vcm->sessions_lockp);
     }
 
@@ -2722,7 +2722,7 @@ vppcom_session_accept (uint32_t listen_session_index, vppcom_endpt_t * ep,
 {
   session_t *listen_session = 0;
   session_t *client_session = 0;
-  u32 client_session_index = ~0;
+  u32 client_session_index = ~0, n_fifos;
   int rv;
   f64 wait_for;
   char *cut_thru_str;
@@ -2821,9 +2821,6 @@ vppcom_session_accept (uint32_t listen_session_index, vppcom_endpt_t * ep,
 	format ((u8 *) a->segment_name, "%d:segment%d%c",
 		getpid (), vcm->unique_segment_index++, 0);
       a->segment_size = vcm->cfg.segment_size;
-      a->preallocated_fifo_pairs = vcm->cfg.preallocated_fifo_pairs;
-      a->rx_fifo_size = vcm->cfg.rx_fifo_size;
-      a->tx_fifo_size = vcm->cfg.tx_fifo_size;
 
       rv = svm_fifo_segment_create (a);
       if (PREDICT_FALSE (rv))
@@ -2850,6 +2847,14 @@ vppcom_session_accept (uint32_t listen_session_index, vppcom_endpt_t * ep,
       vec_free (a->new_segment_indices);
 
       seg = svm_fifo_segment_get_segment (client_session->sm_seg_index);
+      if (vcm->cfg.preallocated_fifo_pairs)
+	{
+	  n_fifos = vcm->cfg.preallocated_fifo_pairs;
+	  svm_fifo_segment_preallocate_fifo_pairs (seg, vcm->cfg.rx_fifo_size,
+						   vcm->cfg.tx_fifo_size,
+						   &n_fifos);
+	}
+
       client_session->server_rx_fifo =
 	svm_fifo_segment_alloc_fifo (seg, vcm->cfg.rx_fifo_size,
 				     FIFO_SEGMENT_RX_FREELIST);
diff --git a/src/vnet/session-apps/echo_client.c b/src/vnet/session-apps/echo_client.c
index c38b5339453..27e253a9235 100644
--- a/src/vnet/session-apps/echo_client.c
+++ b/src/vnet/session-apps/echo_client.c
@@ -413,13 +413,21 @@ echo_clients_rx_callback (stream_session_t * s)
   return 0;
 }
 
+int
+echo_client_add_segment_callback (u32 client_index, const ssvm_private_t * sp)
+{
+  /* New heaps may be added */
+  return 0;
+}
+
 /* *INDENT-OFF* */
 static session_cb_vft_t echo_clients = {
   .session_reset_callback = echo_clients_session_reset_callback,
   .session_connected_callback = echo_clients_session_connected_callback,
   .session_accept_callback = echo_clients_session_create_callback,
   .session_disconnect_callback = echo_clients_session_disconnect_callback,
-  .builtin_server_rx_callback = echo_clients_rx_callback
+  .builtin_server_rx_callback = echo_clients_rx_callback,
+  .add_segment_callback = echo_client_add_segment_callback
 };
 /* *INDENT-ON* */
 
@@ -445,6 +453,7 @@ echo_clients_attach (u8 * appns_id, u64 appns_flags, u64 appns_secret)
 
   options[APP_OPTIONS_ACCEPT_COOKIE] = 0x12345678;
   options[APP_OPTIONS_SEGMENT_SIZE] = segment_size;
+  options[APP_OPTIONS_ADD_SEGMENT_SIZE] = segment_size;
   options[APP_OPTIONS_RX_FIFO_SIZE] = ecm->fifo_size;
   options[APP_OPTIONS_TX_FIFO_SIZE] = ecm->fifo_size;
   options[APP_OPTIONS_PRIVATE_SEGMENT_COUNT] = ecm->private_segment_count;
@@ -625,7 +634,7 @@ echo_clients_command_fn (vlib_main_t * vm,
       else if (unformat (input, "test-bytes"))
 	ecm->test_bytes = 1;
       else
-	return clib_error_return (0, "unknown input `%U'",
+	return clib_error_return (0, "failed: unknown input `%U'",
 				  format_unformat_error, input);
     }
 
diff --git a/src/vnet/session-apps/echo_server.c b/src/vnet/session-apps/echo_server.c
index 37a51d507fc..024ffa66f96 100644
--- a/src/vnet/session-apps/echo_server.c
+++ b/src/vnet/session-apps/echo_server.c
@@ -96,8 +96,8 @@ echo_server_session_connected_callback (u32 app_index, u32 api_context,
 int
 echo_server_add_segment_callback (u32 client_index, const ssvm_private_t * sp)
 {
-  clib_warning ("called...");
-  return -1;
+  /* New heaps may be added */
+  return 0;
 }
 
 int
@@ -290,6 +290,7 @@ echo_server_attach (u8 * appns_id, u64 appns_flags, u64 appns_secret)
   a->session_cb_vft = &echo_server_session_cb_vft;
   a->options = options;
   a->options[APP_OPTIONS_SEGMENT_SIZE] = segment_size;
+  a->options[APP_OPTIONS_ADD_SEGMENT_SIZE] = segment_size;
   a->options[APP_OPTIONS_RX_FIFO_SIZE] = esm->fifo_size;
   a->options[APP_OPTIONS_TX_FIFO_SIZE] = esm->fifo_size;
   a->options[APP_OPTIONS_PRIVATE_SEGMENT_COUNT] = esm->private_segment_count;
diff --git a/src/vnet/session/application.c b/src/vnet/session/application.c
index bd708fc864e..71fc93f960f 100644
--- a/src/vnet/session/application.c
+++ b/src/vnet/session/application.c
@@ -146,7 +146,6 @@ application_new ()
 void
 application_del (application_t * app)
 {
-  segment_manager_properties_t *props;
   vnet_unbind_args_t _a, *a = &_a;
   segment_manager_t *sm;
   u64 handle, *handles = 0;
@@ -208,8 +207,6 @@ application_del (application_t * app)
 	  segment_manager_del (sm);
 	}
     }
-  props = segment_manager_properties_get (app->sm_properties);
-  segment_manager_properties_free (props);
   application_table_del (app);
   pool_put (app_pool, app);
 }
@@ -258,8 +255,8 @@ int
 application_init (application_t * app, u32 api_client_index, u64 * options,
 		  session_cb_vft_t * cb_fns)
 {
-  ssvm_segment_type_t st = SSVM_SEGMENT_MEMFD;
-  u32 app_evt_queue_size, first_seg_size;
+  u32 app_evt_queue_size, first_seg_size, prealloc_fifo_pairs;
+  ssvm_segment_type_t seg_type = SSVM_SEGMENT_MEMFD;
   segment_manager_properties_t *props;
   vl_api_registration_t *reg;
   segment_manager_t *sm;
@@ -268,16 +265,21 @@ application_init (application_t * app, u32 api_client_index, u64 * options,
   /*
    * Make sure we support the requested configuration
    */
-  reg = vl_api_client_index_to_registration (api_client_index);
-  if (!reg)
-    return VNET_API_ERROR_APP_UNSUPPORTED_CFG;
 
-  if (options[APP_OPTIONS_FLAGS] & APP_OPTIONS_FLAGS_IS_BUILTIN)
-    st = SSVM_N_SEGMENT_TYPES;
-  else if (vl_api_registration_file_index (reg) == VL_API_INVALID_FI)
-    st = SSVM_SEGMENT_SHM;
+  if (!(options[APP_OPTIONS_FLAGS] & APP_OPTIONS_FLAGS_IS_BUILTIN))
+    {
+      reg = vl_api_client_index_to_registration (api_client_index);
+      if (!reg)
+	return VNET_API_ERROR_APP_UNSUPPORTED_CFG;
+      if (vl_api_registration_file_index (reg) == VL_API_INVALID_FI)
+	seg_type = SSVM_SEGMENT_SHM;
+    }
+  else
+    {
+      seg_type = SSVM_SEGMENT_PRIVATE;
+    }
 
-  if (!application_verify_cfg (st))
+  if (!application_verify_cfg (seg_type))
     return VNET_API_ERROR_APP_UNSUPPORTED_CFG;
 
   /*
@@ -285,8 +287,8 @@ application_init (application_t * app, u32 api_client_index, u64 * options,
    */
   sm = segment_manager_new ();
   sm->app_index = app->index;
-  props = segment_manager_properties_alloc ();
-  app->sm_properties = segment_manager_properties_index (props);
+  props = application_segment_manager_properties (app);
+  segment_manager_properties_init (props);
   if (options[APP_OPTIONS_ADD_SEGMENT_SIZE])
     {
       props->add_segment_size = options[APP_OPTIONS_ADD_SEGMENT_SIZE];
@@ -296,18 +298,15 @@ application_init (application_t * app, u32 api_client_index, u64 * options,
     props->rx_fifo_size = options[APP_OPTIONS_RX_FIFO_SIZE];
   if (options[APP_OPTIONS_TX_FIFO_SIZE])
     props->tx_fifo_size = options[APP_OPTIONS_TX_FIFO_SIZE];
-  props->preallocated_fifo_pairs = options[APP_OPTIONS_PREALLOC_FIFO_PAIRS];
-  props->private_segment_count = options[APP_OPTIONS_PRIVATE_SEGMENT_COUNT];
-  if (options[APP_OPTIONS_FLAGS] & APP_OPTIONS_FLAGS_IS_BUILTIN)
-    props->segment_type = SSVM_N_SEGMENT_TYPES;
-  else
-    props->segment_type = st;
+  props->segment_type = seg_type;
 
   app_evt_queue_size = options[APP_OPTIONS_EVT_QUEUE_SIZE] > 0 ?
     options[APP_OPTIONS_EVT_QUEUE_SIZE] : default_app_evt_queue_size;
   first_seg_size = options[APP_OPTIONS_SEGMENT_SIZE];
-  if ((rv = segment_manager_init (sm, app->sm_properties, first_seg_size,
-				  app_evt_queue_size)))
+  prealloc_fifo_pairs = options[APP_OPTIONS_PREALLOC_FIFO_PAIRS];
+
+  if ((rv = segment_manager_init (sm, first_seg_size, app_evt_queue_size,
+				  prealloc_fifo_pairs)))
     return rv;
   sm->first_is_protected = 1;
 
@@ -321,15 +320,13 @@ application_init (application_t * app, u32 api_client_index, u64 * options,
   app->ns_index = options[APP_OPTIONS_NAMESPACE];
   app->listeners_table = hash_create (0, sizeof (u64));
   app->proxied_transports = options[APP_OPTIONS_PROXY_TRANSPORT];
+  app->event_queue = segment_manager_event_queue (sm);
 
   /* If no scope enabled, default to global */
   if (!application_has_global_scope (app)
       && !application_has_local_scope (app))
     app->flags |= APP_OPTIONS_FLAGS_USE_GLOBAL_SCOPE;
 
-  /* Allocate app event queue in the first shared-memory segment */
-  app->event_queue = segment_manager_alloc_queue (sm, app_evt_queue_size);
-
   /* Check that the obvious things are properly set up */
   application_verify_cb_fns (cb_fns);
 
@@ -377,7 +374,7 @@ application_alloc_segment_manager (application_t * app)
     }
 
   sm = segment_manager_new ();
-  sm->properties_index = app->sm_properties;
+  sm->app_index = app->index;
 
   return sm;
 }
@@ -520,17 +517,14 @@ application_is_builtin_proxy (application_t * app)
   return (application_is_proxy (app) && application_is_builtin (app));
 }
 
+/**
+ * Send an API message to the external app, to map new segment
+ */
 int
-application_add_segment_notify (u32 app_index, u32 fifo_segment_index)
+application_add_segment_notify (u32 app_index, ssvm_private_t * fs)
 {
   application_t *app = application_get (app_index);
-  svm_fifo_segment_private_t *fs;
-
-  /* Send an API message to the external app, to map new segment */
-  ASSERT (app->cb_fns.add_segment_callback);
-
-  fs = segment_manager_get_segment (fifo_segment_index);
-  return app->cb_fns.add_segment_callback (app->api_client_index, &fs->ssvm);
+  return app->cb_fns.add_segment_callback (app->api_client_index, fs);
 }
 
 u8
@@ -699,8 +693,6 @@ application_setup_proxy (application_t * app)
   transport_proto_t tp;
 
   ASSERT (application_is_proxy (app));
-  if (application_is_builtin (app))
-    return;
 
   /* *INDENT-OFF* */
   transport_proto_foreach (tp, ({
@@ -726,6 +718,19 @@ application_remove_proxy (application_t * app)
   /* *INDENT-ON* */
 }
 
+segment_manager_properties_t *
+application_segment_manager_properties (application_t * app)
+{
+  return &app->sm_properties;
+}
+
+segment_manager_properties_t *
+application_get_segment_manager_properties (u32 app_index)
+{
+  application_t *app = application_get (app_index);
+  return &app->sm_properties;
+}
+
 u8 *
 format_application_listener (u8 * s, va_list * args)
 {
@@ -766,10 +771,10 @@ format_application_listener (u8 * s, va_list * args)
 void
 application_format_connects (application_t * app, int verbose)
 {
+  svm_fifo_segment_private_t *fifo_segment;
   vlib_main_t *vm = vlib_get_main ();
   segment_manager_t *sm;
   u8 *app_name, *s = 0;
-  int j;
 
   /* Header */
   if (app == 0)
@@ -790,15 +795,14 @@ application_format_connects (application_t * app, int verbose)
 
   /* Across all fifo segments */
   sm = segment_manager_get (app->connects_seg_manager);
-  for (j = 0; j < vec_len (sm->segment_indices); j++)
-    {
-      svm_fifo_segment_private_t *fifo_segment;
-      svm_fifo_t *fifo;
-      u8 *str;
 
-      fifo_segment = svm_fifo_segment_get_segment (sm->segment_indices[j]);
-      fifo = svm_fifo_segment_get_fifo_list (fifo_segment);
-      while (fifo)
+  /* *INDENT-OFF* */
+  segment_manager_foreach_segment_w_lock (fifo_segment, sm, ({
+    svm_fifo_t *fifo;
+    u8 *str;
+
+    fifo = svm_fifo_segment_get_fifo_list (fifo_segment);
+    while (fifo)
 	{
 	  u32 session_index, thread_index;
 	  stream_session_t *session;
@@ -821,8 +825,9 @@ application_format_connects (application_t * app, int verbose)
 
 	  fifo = fifo->next;
 	}
-      vec_free (s);
-    }
+    vec_free (s);
+  }));
+  /* *INDENT-ON* */
 
   vec_free (app_name);
 }
@@ -851,7 +856,7 @@ format_application (u8 * s, va_list * args)
 
   app_name = app_get_name_from_reg_index (app);
   app_ns_name = app_namespace_id_from_index (app->ns_index);
-  props = segment_manager_properties_get (app->sm_properties);
+  props = application_segment_manager_properties (app);
   if (verbose)
     s =
       format (s, "%-10d%-20s%-15d%-15d%-15d%-15d%-15d", app->index, app_name,
@@ -894,21 +899,20 @@ show_app_command_fn (vlib_main_t * vm, unformat_input_t * input,
       if (pool_elts (app_pool))
 	{
 	  vlib_cli_output (vm, "%U", format_application_listener,
-			   0 /* header */ , 0, 0,
-			   verbose);
+			   0 /* header */ , 0, 0, verbose);
+
 	  /* *INDENT-OFF* */
-          pool_foreach (app, app_pool,
-          ({
+          pool_foreach (app, app_pool, ({
             /* App's listener sessions */
             if (hash_elts (app->listeners_table) == 0)
               continue;
-            hash_foreach (handle, index, app->listeners_table,
-	    ({
+            hash_foreach (handle, index, app->listeners_table, ({
               vlib_cli_output (vm, "%U", format_application_listener, app,
               			       handle, index, verbose);
             }));
           }));
           /* *INDENT-ON* */
+
 	}
       else
 	vlib_cli_output (vm, "No active server bindings");
diff --git a/src/vnet/session/application.h b/src/vnet/session/application.h
index afe738f199c..36ae6fce8b2 100644
--- a/src/vnet/session/application.h
+++ b/src/vnet/session/application.h
@@ -97,7 +97,7 @@ typedef struct _application
   u8 first_segment_manager_in_use;
 
   /** Segment manager properties. Shared by all segment managers */
-  u32 sm_properties;
+  segment_manager_properties_t sm_properties;
 
   u16 proxied_transports;
 } application_t;
@@ -132,7 +132,7 @@ segment_manager_t *application_get_connect_segment_manager (application_t *
 int application_is_proxy (application_t * app);
 int application_is_builtin (application_t * app);
 int application_is_builtin_proxy (application_t * app);
-int application_add_segment_notify (u32 app_index, u32 fifo_segment_index);
+int application_add_segment_notify (u32 app_index, ssvm_private_t * fs);
 u32 application_session_table (application_t * app, u8 fib_proto);
 u32 application_local_session_table (application_t * app);
 u8 *application_name_from_index (u32 app_index);
@@ -146,6 +146,11 @@ stream_session_t *application_first_listener (application_t * app,
 void application_setup_proxy (application_t * app);
 void application_remove_proxy (application_t * app);
 
+segment_manager_properties_t *application_get_segment_manager_properties (u32
+									  app_index);
+segment_manager_properties_t
+  * application_segment_manager_properties (application_t * app);
+
 #endif /* SRC_VNET_SESSION_APPLICATION_H_ */
 
 /*
diff --git a/src/vnet/session/application_interface.c b/src/vnet/session/application_interface.c
index ad4c28b3c77..efdd3dde9ad 100644
--- a/src/vnet/session/application_interface.c
+++ b/src/vnet/session/application_interface.c
@@ -406,7 +406,7 @@ vnet_application_attach (vnet_app_attach_args_t * a)
 
   a->app_event_queue_address = pointer_to_uword (app->event_queue);
   sm = segment_manager_get (app->first_segment_manager);
-  fs = segment_manager_get_segment (sm->segment_indices[0]);
+  fs = segment_manager_get_segment_w_lock (sm, 0);
 
   if (application_is_proxy (app))
     application_setup_proxy (app);
@@ -415,6 +415,8 @@ vnet_application_attach (vnet_app_attach_args_t * a)
   a->segment = &fs->ssvm;
   a->app_index = app->index;
 
+  segment_manager_segment_reader_unlock (sm);
+
   return 0;
 }
 
diff --git a/src/vnet/session/segment_manager.c b/src/vnet/session/segment_manager.c
index 83b838840d2..f8af3fb45c8 100644
--- a/src/vnet/session/segment_manager.c
+++ b/src/vnet/session/segment_manager.c
@@ -17,88 +17,147 @@
 #include <vnet/session/session.h>
 #include <vnet/session/application.h>
 
-/**
- * Counter used to build segment names
- */
-u32 segment_name_counter = 0;
-
-/**
- * Pool of segment managers
- */
-segment_manager_t *segment_managers = 0;
-
-/*
- * Pool of segment manager properties
- */
-static segment_manager_properties_t *segment_manager_properties_pool;
+segment_manager_main_t segment_manager_main;
 
 /**
- * Process private segment index
+ * Counter used to build segment names
  */
-u32 *private_segment_indices;
+static u32 segment_name_counter = 0;
 
 /**
  * Default fifo and segment size. TODO config.
  */
-u32 default_fifo_size = 1 << 16;
+u32 default_fifo_size = 1 << 12;
 u32 default_segment_size = 1 << 20;
 
 segment_manager_properties_t *
-segment_manager_properties_alloc (void)
+segment_manager_properties_get (segment_manager_t * sm)
+{
+  return application_get_segment_manager_properties (sm->app_index);
+}
+
+segment_manager_properties_t *
+segment_manager_properties_init (segment_manager_properties_t * props)
 {
-  segment_manager_properties_t *props;
-  pool_get (segment_manager_properties_pool, props);
-  memset (props, 0, sizeof (*props));
   props->add_segment_size = default_segment_size;
   props->rx_fifo_size = default_fifo_size;
   props->tx_fifo_size = default_fifo_size;
   return props;
 }
 
+static u8
+segment_manager_app_detached (segment_manager_t * sm)
+{
+  return (sm->app_index == SEGMENT_MANAGER_INVALID_APP_INDEX);
+}
+
 void
-segment_manager_properties_free (segment_manager_properties_t * props)
+segment_manager_app_detach (segment_manager_t * sm)
 {
-  pool_put (segment_manager_properties_pool, props);
-  memset (props, 0xFB, sizeof (*props));
+  sm->app_index = SEGMENT_MANAGER_INVALID_APP_INDEX;
 }
 
-segment_manager_properties_t *
-segment_manager_properties_get (u32 smp_index)
+always_inline u32
+segment_manager_segment_index (segment_manager_t * sm,
+			       svm_fifo_segment_private_t * seg)
+{
+  return (seg - sm->segments);
+}
+
+/**
+ * Remove segment without lock
+ */
+always_inline void
+segment_manager_del_segment (segment_manager_t * sm,
+			     svm_fifo_segment_private_t * fs)
 {
-  if (pool_is_free_index (segment_manager_properties_pool, smp_index))
-    return 0;
-  return pool_elt_at_index (segment_manager_properties_pool, smp_index);
+  segment_manager_main_t *smm = &segment_manager_main;
+
+  if (ssvm_type (&fs->ssvm) != SSVM_SEGMENT_PRIVATE)
+    clib_valloc_free (&smm->va_allocator, fs->ssvm.requested_va);
+
+  ssvm_delete (&fs->ssvm);
+
+  if (CLIB_DEBUG)
+    memset (fs, 0xfb, sizeof (*fs));
+  pool_put (sm->segments, fs);
 }
 
-u32
-segment_manager_properties_index (segment_manager_properties_t * p)
+/**
+ * Removes segment after acquiring writer lock
+ */
+always_inline void
+segment_manager_lock_and_del_segment (segment_manager_t * sm, u32 fs_index)
 {
-  return p - segment_manager_properties_pool;
+  svm_fifo_segment_private_t *fs;
+  u8 is_prealloc;
+
+  clib_rwlock_writer_lock (&sm->segments_rwlock);
+  fs = segment_manager_get_segment (sm, fs_index);
+  is_prealloc = svm_fifo_segment_flags (fs) & FIFO_SEGMENT_F_IS_PREALLOCATED;
+  if (is_prealloc && !segment_manager_app_detached (sm))
+    {
+      clib_rwlock_writer_unlock (&sm->segments_rwlock);
+      return;
+    }
+
+  segment_manager_del_segment (sm, fs);
+  clib_rwlock_writer_unlock (&sm->segments_rwlock);
 }
 
+/**
+ * Reads a segment from the segment manager's pool without lock
+ */
 svm_fifo_segment_private_t *
-segment_manager_get_segment (u32 segment_index)
+segment_manager_get_segment (segment_manager_t * sm, u32 segment_index)
 {
-  return svm_fifo_segment_get_segment (segment_index);
+  return pool_elt_at_index (sm->segments, segment_index);
+}
+
+/**
+ * Reads a segment from the segment manager's pool and acquires reader lock
+ *
+ * Caller must drop the reader's lock by calling
+ * @ref segment_manager_segment_reader_unlock once it finishes working with
+ * the segment.
+ */
+svm_fifo_segment_private_t *
+segment_manager_get_segment_w_lock (segment_manager_t * sm, u32 segment_index)
+{
+  clib_rwlock_reader_lock (&sm->segments_rwlock);
+  return pool_elt_at_index (sm->segments, segment_index);
+}
+
+void
+segment_manager_segment_reader_unlock (segment_manager_t * sm)
+{
+  clib_rwlock_reader_unlock (&sm->segments_rwlock);
 }
 
 void
-segment_manager_get_segment_info (u32 index, u8 ** name, u32 * size)
+segment_manager_segment_writer_unlock (segment_manager_t * sm)
 {
-  svm_fifo_segment_private_t *s;
-  s = svm_fifo_segment_get_segment (index);
-  *name = s->ssvm.name;
-  *size = s->ssvm.ssvm_size;
+  clib_rwlock_writer_unlock (&sm->segments_rwlock);
 }
 
+/**
+ * Adds segment to segment manager's pool
+ *
+ * If needed a writer's lock is acquired before allocating a new segment
+ * to avoid affecting any of the segments pool readers.
+ */
 always_inline int
-segment_manager_add_segment_i (segment_manager_t * sm, u32 segment_size,
-			       u32 protected_space)
+segment_manager_add_segment (segment_manager_t * sm, u32 segment_size)
 {
-  svm_fifo_segment_create_args_t _ca = { 0 }, *ca = &_ca;
+  segment_manager_main_t *smm = &segment_manager_main;
+  u32 rnd_margin = 128 << 10, seg_index;
   segment_manager_properties_t *props;
+  uword baseva = (u64) ~ 0, alloc_size;
+  svm_fifo_segment_private_t *seg;
+  u8 *seg_name;
+  int rv;
 
-  props = segment_manager_properties_get (sm->properties_index);
+  props = segment_manager_properties_get (sm);
 
   /* Not configured for addition of new segments and not first */
   if (!props->add_segment && !segment_size)
@@ -107,169 +166,174 @@ segment_manager_add_segment_i (segment_manager_t * sm, u32 segment_size,
       return VNET_API_ERROR_INVALID_VALUE;
     }
 
-  ca->segment_size = segment_size ? segment_size : props->add_segment_size;
-  ca->rx_fifo_size = props->rx_fifo_size;
-  ca->tx_fifo_size = props->tx_fifo_size;
-  ca->preallocated_fifo_pairs = props->preallocated_fifo_pairs;
-  ca->seg_protected_space = protected_space ? protected_space : 0;
+  /*
+   * Allocate fifo segment and lock if needed
+   */
+  if (vlib_num_workers ())
+    {
+      clib_rwlock_writer_lock (&sm->segments_rwlock);
+      pool_get (sm->segments, seg);
+    }
+  else
+    {
+      pool_get (sm->segments, seg);
+    }
+  memset (seg, 0, sizeof (*seg));
 
-  if (props->segment_type != SSVM_N_SEGMENT_TYPES)
+  /*
+   * Initialize ssvm segment and svm fifo private header
+   */
+  segment_size = segment_size ? segment_size : props->add_segment_size;
+  if (props->segment_type != SSVM_SEGMENT_PRIVATE)
     {
-      ca->segment_name = (char *) format (0, "%d-%d%c", getpid (),
-					  segment_name_counter++, 0);
-      ca->segment_type = props->segment_type;
-      if (svm_fifo_segment_create (ca))
+      seg_name = format (0, "%d-%d%c", getpid (), segment_name_counter++, 0);
+      alloc_size = segment_size + rnd_margin;
+      baseva = clib_valloc_alloc (&smm->va_allocator, alloc_size, 0);
+      if (!baseva)
 	{
-	  clib_warning ("svm_fifo_segment_create ('%s', %d) failed",
-			ca->segment_name, ca->segment_size);
-	  return VNET_API_ERROR_SVM_SEGMENT_CREATE_FAIL;
+	  clib_warning ("out of space for segments");
+	  return -1;
 	}
-      vec_free (ca->segment_name);
     }
   else
-    {
-      u32 rx_fifo_size, tx_fifo_size;
-      u32 rx_rounded_data_size, tx_rounded_data_size;
-      u32 approx_segment_count;
-      u64 approx_total_size;
-
-      ca->segment_name = "process-private-segment";
-      ca->private_segment_count = props->private_segment_count;
+    seg_name = format (0, "%s%c", "process-private-segment", 0);
 
-      /* Calculate space requirements */
-      rx_rounded_data_size = (1 << (max_log2 (ca->rx_fifo_size)));
-      tx_rounded_data_size = (1 << (max_log2 (ca->tx_fifo_size)));
+  seg->ssvm.ssvm_size = segment_size;
+  seg->ssvm.name = seg_name;
+  seg->ssvm.requested_va = baseva;
 
-      rx_fifo_size = sizeof (svm_fifo_t) + rx_rounded_data_size;
-      tx_fifo_size = sizeof (svm_fifo_t) + tx_rounded_data_size;
-
-      approx_total_size = (u64) ca->preallocated_fifo_pairs
-	* (rx_fifo_size + tx_fifo_size);
-      approx_segment_count = (approx_total_size + protected_space
-			      + (ca->segment_size -
-				 1)) / (u64) ca->segment_size;
+  if ((rv = ssvm_master_init (&seg->ssvm, props->segment_type)))
+    {
+      clib_warning ("svm_master_init ('%v', %u) failed", seg_name,
+		    segment_size);
 
-      /* The user asked us to figure it out... */
-      if (ca->private_segment_count == 0
-	  || approx_segment_count < ca->private_segment_count)
-	{
-	  ca->private_segment_count = approx_segment_count;
-	}
-      /* Follow directions, but issue a warning */
-      else if (approx_segment_count < ca->private_segment_count)
-	{
-	  clib_warning ("Honoring segment count %u, calculated count was %u",
-			ca->private_segment_count, approx_segment_count);
-	}
-      else if (approx_segment_count > ca->private_segment_count)
-	{
-	  clib_warning ("Segment count too low %u, calculated %u.",
-			ca->private_segment_count, approx_segment_count);
-	  return VNET_API_ERROR_INVALID_VALUE;
-	}
+      if (props->segment_type != SSVM_SEGMENT_PRIVATE)
+	clib_valloc_free (&smm->va_allocator, baseva);
+      pool_put (sm->segments, seg);
+      return (rv);
+    }
 
-      if (svm_fifo_segment_create_process_private (ca))
-	clib_warning ("Failed to create process private segment");
+  svm_fifo_segment_init (seg);
 
-      ASSERT (vec_len (ca->new_segment_indices));
-    }
+  /*
+   * Save segment index before dropping lock, if any held
+   */
+  seg_index = seg - sm->segments;
 
-  vec_append (sm->segment_indices, ca->new_segment_indices);
-  vec_free (ca->new_segment_indices);
-  return 0;
-}
+  if (vlib_num_workers ())
+    clib_rwlock_writer_unlock (&sm->segments_rwlock);
 
-int
-segment_manager_add_segment (segment_manager_t * sm)
-{
-  return segment_manager_add_segment_i (sm, 0, 0);
+  return seg_index;
 }
 
 segment_manager_t *
 segment_manager_new ()
 {
+  segment_manager_main_t *smm = &segment_manager_main;
   segment_manager_t *sm;
-  pool_get (segment_managers, sm);
+  pool_get (smm->segment_managers, sm);
   memset (sm, 0, sizeof (*sm));
+  clib_rwlock_init (&sm->segments_rwlock);
   return sm;
 }
 
 /**
  * Initializes segment manager based on options provided.
- * Returns error if svm segment allocation fails.
+ * Returns error if ssvm segment(s) allocation fails.
  */
 int
-segment_manager_init (segment_manager_t * sm, u32 props_index,
-		      u32 first_seg_size, u32 evt_q_size)
+segment_manager_init (segment_manager_t * sm, u32 first_seg_size,
+		      u32 evt_q_size, u32 prealloc_fifo_pairs)
 {
-  u32 protected_space;
-  int rv;
+  u32 rx_fifo_size, tx_fifo_size, pair_size;
+  u32 rx_rounded_data_size, tx_rounded_data_size;
+  u64 approx_total_size, max_seg_size =
+    ((u64) 1 << 32) - clib_mem_get_page_size ();
+  segment_manager_properties_t *props;
+  svm_fifo_segment_private_t *segment;
+  u32 approx_segment_count;
+  int seg_index, i;
 
-  sm->properties_index = props_index;
+  props = segment_manager_properties_get (sm);
+  first_seg_size = clib_max (first_seg_size, default_segment_size);
 
-  protected_space = max_pow2 (sizeof (svm_queue_t)
-			      + evt_q_size * sizeof (session_fifo_event_t));
-  protected_space = round_pow2_u64 (protected_space, CLIB_CACHE_LINE_BYTES);
-  first_seg_size = first_seg_size > 0 ? first_seg_size : default_segment_size;
-  rv = segment_manager_add_segment_i (sm, first_seg_size, protected_space);
-  if (rv)
+  if (prealloc_fifo_pairs)
     {
-      clib_warning ("Failed to allocate segment");
-      return rv;
-    }
+      /* Figure out how many segments should be preallocated */
+      rx_rounded_data_size = (1 << (max_log2 (props->rx_fifo_size)));
+      tx_rounded_data_size = (1 << (max_log2 (props->tx_fifo_size)));
 
-  clib_spinlock_init (&sm->lockp);
-  return 0;
-}
+      rx_fifo_size = sizeof (svm_fifo_t) + rx_rounded_data_size;
+      tx_fifo_size = sizeof (svm_fifo_t) + tx_rounded_data_size;
+      pair_size = rx_fifo_size + tx_fifo_size;
 
-u8
-segment_manager_has_fifos (segment_manager_t * sm)
-{
-  svm_fifo_segment_private_t *segment;
-  int i;
+      approx_total_size = (u64) prealloc_fifo_pairs *pair_size;
+      if (first_seg_size > approx_total_size)
+	max_seg_size = first_seg_size;
+      approx_segment_count = (approx_total_size + (max_seg_size - 1))
+	/ max_seg_size;
 
-  for (i = 0; i < vec_len (sm->segment_indices); i++)
+      /* Allocate the segments */
+      for (i = 0; i < approx_segment_count + 1; i++)
+	{
+	  seg_index = segment_manager_add_segment (sm, max_seg_size);
+	  if (seg_index < 0)
+	    {
+	      clib_warning ("Failed to preallocate segment %d", i);
+	      return seg_index;
+	    }
+
+	  if (i == 0)
+	    sm->event_queue = segment_manager_alloc_queue (sm, evt_q_size);
+
+	  segment = segment_manager_get_segment (sm, seg_index);
+	  svm_fifo_segment_preallocate_fifo_pairs (segment,
+						   props->rx_fifo_size,
+						   props->tx_fifo_size,
+						   &prealloc_fifo_pairs);
+	  svm_fifo_segment_flags (segment) = FIFO_SEGMENT_F_IS_PREALLOCATED;
+	  if (prealloc_fifo_pairs == 0)
+	    break;
+	}
+    }
+  else
     {
-      segment = svm_fifo_segment_get_segment (sm->segment_indices[i]);
-      if (CLIB_DEBUG && i && !svm_fifo_segment_has_fifos (segment)
-	  && !(segment->h->flags & FIFO_SEGMENT_F_IS_PREALLOCATED))
-	clib_warning ("segment %d has no fifos!", sm->segment_indices[i]);
-      if (svm_fifo_segment_has_fifos (segment))
-	return 1;
+      seg_index = segment_manager_add_segment (sm, first_seg_size);
+      if (seg_index)
+	{
+	  clib_warning ("Failed to allocate segment");
+	  return seg_index;
+	}
+      sm->event_queue = segment_manager_alloc_queue (sm, evt_q_size);
     }
-  return 0;
-}
 
-static u8
-segment_manager_app_detached (segment_manager_t * sm)
-{
-  return (sm->app_index == SEGMENT_MANAGER_INVALID_APP_INDEX);
+  return 0;
 }
 
-void
-segment_manager_app_detach (segment_manager_t * sm)
+u8
+segment_manager_has_fifos (segment_manager_t * sm)
 {
-  sm->app_index = SEGMENT_MANAGER_INVALID_APP_INDEX;
-}
+  svm_fifo_segment_private_t *seg;
+  u8 first = 1;
+
+  /* *INDENT-OFF* */
+  segment_manager_foreach_segment_w_lock (seg, sm, ({
+    if (CLIB_DEBUG && !first && !svm_fifo_segment_has_fifos (seg)
+	&& !(svm_fifo_segment_flags (seg) & FIFO_SEGMENT_F_IS_PREALLOCATED))
+      {
+	clib_warning ("segment %d has no fifos!",
+	              segment_manager_segment_index (sm, seg));
+	first = 0;
+      }
+    if (svm_fifo_segment_has_fifos (seg))
+      {
+	segment_manager_segment_reader_unlock (sm);
+	return 1;
+      }
+  }));
+  /* *INDENT-ON* */
 
-static void
-segment_manager_del_segment (segment_manager_t * sm, u32 segment_index)
-{
-  svm_fifo_segment_private_t *fifo_segment;
-  u32 svm_segment_index;
-  clib_spinlock_lock (&sm->lockp);
-  svm_segment_index = vec_elt (sm->segment_indices, segment_index);
-  fifo_segment = svm_fifo_segment_get_segment (svm_segment_index);
-  if (!fifo_segment
-      || ((fifo_segment->h->flags & FIFO_SEGMENT_F_IS_PREALLOCATED)
-	  && !segment_manager_app_detached (sm)))
-    {
-      clib_spinlock_unlock (&sm->lockp);
-      return;
-    }
-  svm_fifo_segment_delete (fifo_segment);
-  vec_del1 (sm->segment_indices, segment_index);
-  clib_spinlock_unlock (&sm->lockp);
+  return 0;
 }
 
 /**
@@ -278,42 +342,35 @@ segment_manager_del_segment (segment_manager_t * sm, u32 segment_index)
 void
 segment_manager_del_sessions (segment_manager_t * sm)
 {
-  int j;
   svm_fifo_segment_private_t *fifo_segment;
+  stream_session_t *session;
   svm_fifo_t *fifo;
 
-  ASSERT (vec_len (sm->segment_indices));
+  ASSERT (pool_elts (sm->segments) != 0);
 
   /* Across all fifo segments used by the server */
-  for (j = 0; j < vec_len (sm->segment_indices); j++)
-    {
-      fifo_segment = svm_fifo_segment_get_segment (sm->segment_indices[j]);
-      fifo = svm_fifo_segment_get_fifo_list (fifo_segment);
-
-      /*
-       * Remove any residual sessions from the session lookup table
-       * Don't bother deleting the individual fifos, we're going to
-       * throw away the fifo segment in a minute.
-       */
-      while (fifo)
-	{
-	  u32 session_index, thread_index;
-	  stream_session_t *session;
-
-	  session_index = fifo->master_session_index;
-	  thread_index = fifo->master_thread_index;
-	  session = session_get (session_index, thread_index);
-
-	  /* Instead of directly removing the session call disconnect */
-	  if (session->session_state != SESSION_STATE_CLOSED)
-	    stream_session_disconnect (session);
-	  fifo = fifo->next;
-	}
-
-      /* Instead of removing the segment, test when cleaning up disconnected
-       * sessions if the segment can be removed.
-       */
-    }
+  /* *INDENT-OFF* */
+  segment_manager_foreach_segment_w_lock (fifo_segment, sm, ({
+    fifo = svm_fifo_segment_get_fifo_list (fifo_segment);
+
+    /*
+     * Remove any residual sessions from the session lookup table
+     * Don't bother deleting the individual fifos, we're going to
+     * throw away the fifo segment in a minute.
+     */
+    while (fifo)
+      {
+	session = session_get (fifo->master_session_index,
+	                       fifo->master_thread_index);
+	stream_session_disconnect (session);
+	fifo = fifo->next;
+      }
+
+    /* Instead of removing the segment, test when cleaning up disconnected
+     * sessions if the segment can be removed.
+     */
+  }));
+  /* *INDENT-ON* */
 }
 
 /**
@@ -326,7 +383,8 @@ segment_manager_del_sessions (segment_manager_t * sm)
 void
 segment_manager_del (segment_manager_t * sm)
 {
-  int i;
+  segment_manager_main_t *smm = &segment_manager_main;
+  svm_fifo_segment_private_t *fifo_segment;
 
   ASSERT (!segment_manager_has_fifos (sm)
 	  && segment_manager_app_detached (sm));
@@ -335,20 +393,20 @@ segment_manager_del (segment_manager_t * sm)
    * them now. Apart from that, the first segment in the first segment manager
    * is not removed when all fifos are removed. It can only be removed when
    * the manager is explicitly deleted/detached by the app. */
-  for (i = vec_len (sm->segment_indices) - 1; i >= 0; i--)
-    {
-      if (CLIB_DEBUG)
-	{
-	  svm_fifo_segment_private_t *segment;
-	  segment = svm_fifo_segment_get_segment (sm->segment_indices[i]);
-	  ASSERT (!svm_fifo_segment_has_fifos (segment));
-	}
-      segment_manager_del_segment (sm, i);
-    }
-  clib_spinlock_free (&sm->lockp);
+  clib_rwlock_writer_lock (&sm->segments_rwlock);
+
+  /* *INDENT-OFF* */
+  pool_foreach (fifo_segment, sm->segments, ({
+    segment_manager_del_segment (sm, fifo_segment);
+  }));
+  /* *INDENT-ON* */
+
+  clib_rwlock_writer_unlock (&sm->segments_rwlock);
+
+  clib_rwlock_free (&sm->segments_rwlock);
   if (CLIB_DEBUG)
     memset (sm, 0xfe, sizeof (*sm));
-  pool_put (segment_managers, sm);
+  pool_put (smm->segment_managers, sm);
 }
 
 void
@@ -364,6 +422,44 @@ segment_manager_init_del (segment_manager_t * sm)
     }
 }
 
+always_inline int
+segment_try_alloc_fifos (svm_fifo_segment_private_t * fifo_segment,
+			 u32 rx_fifo_size, u32 tx_fifo_size,
+			 svm_fifo_t ** rx_fifo, svm_fifo_t ** tx_fifo)
+{
+  rx_fifo_size = clib_max (rx_fifo_size, default_fifo_size);
+  *rx_fifo = svm_fifo_segment_alloc_fifo (fifo_segment, rx_fifo_size,
+					  FIFO_SEGMENT_RX_FREELIST);
+
+  tx_fifo_size = clib_max (tx_fifo_size, default_fifo_size);
+  *tx_fifo = svm_fifo_segment_alloc_fifo (fifo_segment, tx_fifo_size,
+					  FIFO_SEGMENT_TX_FREELIST);
+
+  if (*rx_fifo == 0)
+    {
+      /* This would be very odd, but handle it... */
+      if (*tx_fifo != 0)
+	{
+	  svm_fifo_segment_free_fifo (fifo_segment, *tx_fifo,
+				      FIFO_SEGMENT_TX_FREELIST);
+	  *tx_fifo = 0;
+	}
+      return -1;
+    }
+  if (*tx_fifo == 0)
+    {
+      if (*rx_fifo != 0)
+	{
+	  svm_fifo_segment_free_fifo (fifo_segment, *rx_fifo,
+				      FIFO_SEGMENT_RX_FREELIST);
+	  *rx_fifo = 0;
+	}
+      return -1;
+    }
+
+  return 0;
+}
+
 int
 segment_manager_alloc_session_fifos (segment_manager_t * sm,
 				     svm_fifo_t ** rx_fifo,
@@ -371,119 +467,93 @@ segment_manager_alloc_session_fifos (segment_manager_t * sm,
 				     u32 * fifo_segment_index)
 {
   svm_fifo_segment_private_t *fifo_segment;
+  int alloc_fail = 1, rv = 0, new_fs_index;
   segment_manager_properties_t *props;
-  u32 fifo_size, sm_index;
   u8 added_a_segment = 0;
-  int i;
+  u32 sm_index;
+
+  ASSERT (pool_elts (sm->segments) != 0);
+  props = segment_manager_properties_get (sm);
 
-  ASSERT (vec_len (sm->segment_indices));
+  /*
+   * Find the first free segment to allocate the fifos in
+   */
 
-  /* Make sure we don't have multiple threads trying to allocate segments
-   * at the same time. */
-  clib_spinlock_lock (&sm->lockp);
+  /* *INDENT-OFF* */
+  segment_manager_foreach_segment_w_lock (fifo_segment, sm, ({
+    alloc_fail = segment_try_alloc_fifos (fifo_segment, props->rx_fifo_size,
+                                          props->tx_fifo_size, rx_fifo,
+                                          tx_fifo);
+    /* Exit with lock held, drop it after notifying app */
+    if (!alloc_fail)
+      goto alloc_success;
+  }));
+  /* *INDENT-ON* */
 
-  /* Allocate svm fifos */
-  props = segment_manager_properties_get (sm->properties_index);
-again:
-  for (i = 0; i < vec_len (sm->segment_indices); i++)
+alloc_check:
+
+  if (!alloc_fail)
     {
-      *fifo_segment_index = vec_elt (sm->segment_indices, i);
-      fifo_segment = svm_fifo_segment_get_segment (*fifo_segment_index);
 
-      fifo_size = props->rx_fifo_size;
-      fifo_size = (fifo_size == 0) ? default_fifo_size : fifo_size;
-      *rx_fifo = svm_fifo_segment_alloc_fifo (fifo_segment, fifo_size,
-					      FIFO_SEGMENT_RX_FREELIST);
+    alloc_success:
 
-      fifo_size = props->tx_fifo_size;
-      fifo_size = (fifo_size == 0) ? default_fifo_size : fifo_size;
-      *tx_fifo = svm_fifo_segment_alloc_fifo (fifo_segment, fifo_size,
-					      FIFO_SEGMENT_TX_FREELIST);
+      ASSERT (rx_fifo && tx_fifo);
+      sm_index = segment_manager_index (sm);
+      (*tx_fifo)->segment_manager = sm_index;
+      (*rx_fifo)->segment_manager = sm_index;
+      *fifo_segment_index = segment_manager_segment_index (sm, fifo_segment);
 
-      if (*rx_fifo == 0)
-	{
-	  /* This would be very odd, but handle it... */
-	  if (*tx_fifo != 0)
-	    {
-	      svm_fifo_segment_free_fifo (fifo_segment, *tx_fifo,
-					  FIFO_SEGMENT_TX_FREELIST);
-	      *tx_fifo = 0;
-	    }
-	  continue;
-	}
-      if (*tx_fifo == 0)
-	{
-	  if (*rx_fifo != 0)
-	    {
-	      svm_fifo_segment_free_fifo (fifo_segment, *rx_fifo,
-					  FIFO_SEGMENT_RX_FREELIST);
-	      *rx_fifo = 0;
-	    }
-	  continue;
-	}
-      break;
+      if (added_a_segment)
+	rv = application_add_segment_notify (sm->app_index,
+					     &fifo_segment->ssvm);
+      /* Drop the lock after app is notified */
+      segment_manager_segment_reader_unlock (sm);
+      return rv;
     }
 
-  /* See if we're supposed to create another segment */
-  if (*rx_fifo == 0)
+  /*
+   * Allocation failed, see if we can add a new segment
+   */
+  if (props->add_segment)
     {
-      if (props->add_segment && !props->segment_type)
+      if (added_a_segment)
 	{
-	  if (added_a_segment)
-	    {
-	      clib_warning ("added a segment, still can't allocate a fifo");
-	      clib_spinlock_unlock (&sm->lockp);
-	      return SESSION_ERROR_NEW_SEG_NO_SPACE;
-	    }
-
-	  if (segment_manager_add_segment (sm))
-	    {
-	      clib_spinlock_unlock (&sm->lockp);
-	      return VNET_API_ERROR_URI_FIFO_CREATE_FAILED;
-	    }
-
-	  added_a_segment = 1;
-	  goto again;
+	  clib_warning ("Added a segment, still can't allocate a fifo");
+	  segment_manager_segment_reader_unlock (sm);
+	  return SESSION_ERROR_NEW_SEG_NO_SPACE;
 	}
-      else
+      if ((new_fs_index = segment_manager_add_segment (sm, 0)) < 0)
 	{
-	  clib_warning ("No space to allocate fifos!");
-	  clib_spinlock_unlock (&sm->lockp);
-	  return SESSION_ERROR_NO_SPACE;
+	  clib_warning ("Failed to add new segment");
+	  return SESSION_ERROR_SEG_CREATE;
 	}
+      fifo_segment = segment_manager_get_segment_w_lock (sm, new_fs_index);
+      alloc_fail = segment_try_alloc_fifos (fifo_segment, props->rx_fifo_size,
+					    props->tx_fifo_size, rx_fifo,
+					    tx_fifo);
+      added_a_segment = 1;
+      goto alloc_check;
+    }
+  else
+    {
+      clib_warning ("Can't add new seg and no space to allocate fifos!");
+      return SESSION_ERROR_NO_SPACE;
     }
-
-  /* Backpointers to segment manager */
-  sm_index = segment_manager_index (sm);
-  (*tx_fifo)->segment_manager = sm_index;
-  (*rx_fifo)->segment_manager = sm_index;
-
-  clib_spinlock_unlock (&sm->lockp);
-
-  if (added_a_segment)
-    return application_add_segment_notify (sm->app_index,
-					   *fifo_segment_index);
-
-  return 0;
 }
 
 void
-segment_manager_dealloc_fifos (u32 svm_segment_index, svm_fifo_t * rx_fifo,
+segment_manager_dealloc_fifos (u32 segment_index, svm_fifo_t * rx_fifo,
 			       svm_fifo_t * tx_fifo)
 {
-  segment_manager_t *sm;
   svm_fifo_segment_private_t *fifo_segment;
-  u32 i, segment_index = ~0;
-  u8 is_first;
-
-  sm = segment_manager_get_if_valid (rx_fifo->segment_manager);
+  segment_manager_t *sm;
 
   /* It's possible to have no segment manager if the session was removed
    * as result of a detach. */
-  if (!sm)
+  if (!(sm = segment_manager_get_if_valid (rx_fifo->segment_manager)))
     return;
 
-  fifo_segment = svm_fifo_segment_get_segment (svm_segment_index);
+  fifo_segment = segment_manager_get_segment_w_lock (sm, segment_index);
   svm_fifo_segment_free_fifo (fifo_segment, rx_fifo,
 			      FIFO_SEGMENT_RX_FREELIST);
   svm_fifo_segment_free_fifo (fifo_segment, tx_fifo,
@@ -497,48 +567,42 @@ segment_manager_dealloc_fifos (u32 svm_segment_index, svm_fifo_t * rx_fifo,
    */
   if (!svm_fifo_segment_has_fifos (fifo_segment))
     {
-      is_first = sm->segment_indices[0] == svm_segment_index;
+      segment_manager_segment_reader_unlock (sm);
 
       /* Remove segment if it holds no fifos or first but not protected */
-      if (!is_first || !sm->first_is_protected)
-	{
-	  /* Find the segment manager segment index */
-	  for (i = 0; i < vec_len (sm->segment_indices); i++)
-	    if (sm->segment_indices[i] == svm_segment_index)
-	      {
-		segment_index = i;
-		break;
-	      }
-	  ASSERT (segment_index != (u32) ~ 0);
-	  segment_manager_del_segment (sm, segment_index);
-	}
+      if (segment_index != 0 || !sm->first_is_protected)
+	segment_manager_lock_and_del_segment (sm, segment_index);
 
       /* Remove segment manager if no sessions and detached from app */
       if (segment_manager_app_detached (sm)
 	  && !segment_manager_has_fifos (sm))
 	segment_manager_del (sm);
     }
+  else
+    segment_manager_segment_reader_unlock (sm);
 }
 
 /**
  * Allocates shm queue in the first segment
+ *
+ * Must be called with lock held
  */
 svm_queue_t *
 segment_manager_alloc_queue (segment_manager_t * sm, u32 queue_size)
 {
-  ssvm_shared_header_t *sh;
   svm_fifo_segment_private_t *segment;
+  ssvm_shared_header_t *sh;
   svm_queue_t *q;
   void *oldheap;
 
-  ASSERT (sm->segment_indices != 0);
+  ASSERT (!pool_is_free_index (sm->segments, 0));
 
-  segment = svm_fifo_segment_get_segment (sm->segment_indices[0]);
+  segment = segment_manager_get_segment (sm, 0);
   sh = segment->ssvm.sh;
 
   oldheap = ssvm_push_heap (sh);
-  q = svm_queue_init (queue_size,
-		      sizeof (session_fifo_event_t), 0 /* consumer pid */ ,
+  q = svm_queue_init (queue_size, sizeof (session_fifo_event_t),
+		      0 /* consumer pid */ ,
 		      0 /* signal when queue non-empty */ );
   ssvm_pop_heap (oldheap);
   return q;
@@ -550,25 +614,42 @@ segment_manager_alloc_queue (segment_manager_t * sm, u32 queue_size)
 void
 segment_manager_dealloc_queue (segment_manager_t * sm, svm_queue_t * q)
 {
-  ssvm_shared_header_t *sh;
   svm_fifo_segment_private_t *segment;
+  ssvm_shared_header_t *sh;
   void *oldheap;
 
-  ASSERT (sm->segment_indices != 0);
+  ASSERT (!pool_is_free_index (sm->segments, 0));
 
-  segment = svm_fifo_segment_get_segment (sm->segment_indices[0]);
+  segment = segment_manager_get_segment_w_lock (sm, 0);
   sh = segment->ssvm.sh;
 
   oldheap = ssvm_push_heap (sh);
   svm_queue_free (q);
   ssvm_pop_heap (oldheap);
+  segment_manager_segment_reader_unlock (sm);
+}
+
+/*
+ * Init segment vm address allocator
+ */
+void
+segment_manager_main_init (segment_manager_main_init_args_t * a)
+{
+  segment_manager_main_t *sm = &segment_manager_main;
+  clib_valloc_chunk_t _ip, *ip = &_ip;
+
+  ip->baseva = a->baseva;
+  ip->size = a->size;
+
+  clib_valloc_init (&sm->va_allocator, ip, 1 /* lock */ );
 }
 
 static clib_error_t *
 segment_manager_show_fn (vlib_main_t * vm, unformat_input_t * input,
 			 vlib_cli_command_t * cmd)
 {
-  svm_fifo_segment_private_t *segments, *seg;
+  segment_manager_main_t *smm = &segment_manager_main;
+  svm_fifo_segment_private_t *seg;
   segment_manager_t *sm;
   u8 show_segments = 0, verbose = 0;
   uword address;
@@ -587,39 +668,38 @@ segment_manager_show_fn (vlib_main_t * vm, unformat_input_t * input,
 				  format_unformat_error, input);
     }
   vlib_cli_output (vm, "%d segment managers allocated",
-		   pool_elts (segment_managers));
-  if (verbose && pool_elts (segment_managers))
+		   pool_elts (smm->segment_managers));
+  if (verbose && pool_elts (smm->segment_managers))
     {
       vlib_cli_output (vm, "%-10s%=15s%=12s", "Index", "App Index",
 		       "Segments");
 
       /* *INDENT-OFF* */
-      pool_foreach (sm, segment_managers, ({
+      pool_foreach (sm, smm->segment_managers, ({
 	vlib_cli_output (vm, "%-10d%=15d%=12d", segment_manager_index(sm),
-			   sm->app_index, vec_len (sm->segment_indices));
+			   sm->app_index, pool_elts (sm->segments));
       }));
       /* *INDENT-ON* */
 
     }
   if (show_segments)
     {
-      segments = svm_fifo_segment_segments_pool ();
-      vlib_cli_output (vm, "%d svm fifo segments allocated",
-		       pool_elts (segments));
       vlib_cli_output (vm, "%-15s%15s%15s%15s%15s%15s", "Name", "Type",
 		       "HeapSize (M)", "ActiveFifos", "FreeFifos", "Address");
 
       /* *INDENT-OFF* */
-      pool_foreach (seg, segments, ({
-	svm_fifo_segment_info (seg, &address, &size);
-	active_fifos = svm_fifo_segment_num_fifos (seg);
-        free_fifos = svm_fifo_segment_num_free_fifos (seg, ~0 /* size */);
-	vlib_cli_output (vm, "%-15v%15U%15llu%15u%15u%15llx",
-	                 ssvm_name (&seg->ssvm), format_svm_fifo_segment_type,
-	                 seg, size >> 20ULL, active_fifos, free_fifos,
-	                 address);
-        if (verbose)
-          vlib_cli_output (vm, "%U", format_svm_fifo_segment, seg, verbose);
+      pool_foreach (sm, smm->segment_managers, ({
+	  segment_manager_foreach_segment_w_lock (seg, sm, ({
+	    svm_fifo_segment_info (seg, &address, &size);
+	    active_fifos = svm_fifo_segment_num_fifos (seg);
+	    free_fifos = svm_fifo_segment_num_free_fifos (seg, ~0 /* size */);
+	    vlib_cli_output (vm, "%-15v%15U%15llu%15u%15u%15llx",
+			     ssvm_name (&seg->ssvm), format_svm_fifo_segment_type,
+			     seg, size >> 20ULL, active_fifos, free_fifos,
+			     address);
+	    if (verbose)
+	      vlib_cli_output (vm, "%U", format_svm_fifo_segment, seg, verbose);
+	  }));
       }));
       /* *INDENT-ON* */
 
diff --git a/src/vnet/session/segment_manager.h b/src/vnet/session/segment_manager.h
index b2a792d206b..9b1d4cd0c06 100644
--- a/src/vnet/session/segment_manager.h
+++ b/src/vnet/session/segment_manager.h
@@ -20,6 +20,7 @@
 #include <svm/queue.h>
 #include <vlibmemory/api.h>
 #include <vppinfra/lock.h>
+#include <vppinfra/valloc.h>
 
 typedef struct _segment_manager_properties
 {
@@ -28,7 +29,7 @@ typedef struct _segment_manager_properties
   u32 tx_fifo_size;
 
   /** Preallocated pool sizes */
-  u32 preallocated_fifo_pairs;
+//  u32 preallocated_fifo_pairs;
 
   /** Configured additional segment size */
   u32 add_segment_size;
@@ -40,33 +41,58 @@ typedef struct _segment_manager_properties
   ssvm_segment_type_t segment_type;
 
   /** Use one or more private mheaps, instead of the global heap */
-  u32 private_segment_count;
+//  u32 private_segment_count;
 } segment_manager_properties_t;
 
 typedef struct _segment_manager
 {
-  clib_spinlock_t lockp;
+  /** Pool of segments allocated by this manager */
+  svm_fifo_segment_private_t *segments;
 
-  /** segments mapped by this manager */
-  u32 *segment_indices;
+  /** rwlock that protects the segments pool */
+  clib_rwlock_t segments_rwlock;
 
   /** Owner app index */
   u32 app_index;
 
   /**
-   * Pointer to manager properties. Could be shared among all of
-   * an app's segment managers s
-   */
-  u32 properties_index;
-
-  /**
    * First segment should not be deleted unless segment manger is deleted.
    * This also indicates that the segment manager is the first to have been
    * allocated for the app.
    */
   u8 first_is_protected;
+
+  /**
+   * App event queue allocated in first segment
+   */
+  svm_queue_t *event_queue;
 } segment_manager_t;
 
+#define segment_manager_foreach_segment_w_lock(VAR, SM, BODY)		\
+do {									\
+    clib_rwlock_reader_lock (&(SM)->segments_rwlock);			\
+    pool_foreach((VAR), ((SM)->segments), (BODY));			\
+    clib_rwlock_reader_unlock (&(SM)->segments_rwlock);			\
+} while (0)
+
+typedef struct segment_manager_main_
+{
+  /** Pool of segment managers */
+  segment_manager_t *segment_managers;
+
+  /** Virtual address allocator */
+  clib_valloc_main_t va_allocator;
+
+} segment_manager_main_t;
+
+extern segment_manager_main_t segment_manager_main;
+
+typedef struct segment_manager_main_init_args_
+{
+  u64 baseva;
+  u64 size;
+} segment_manager_main_init_args_t;
+
 #define SEGMENT_MANAGER_INVALID_APP_INDEX ((u32) ~0)
 
 /** Pool of segment managers */
@@ -75,31 +101,44 @@ extern segment_manager_t *segment_managers;
 always_inline segment_manager_t *
 segment_manager_get (u32 index)
 {
-  return pool_elt_at_index (segment_managers, index);
+  return pool_elt_at_index (segment_manager_main.segment_managers, index);
 }
 
 always_inline segment_manager_t *
 segment_manager_get_if_valid (u32 index)
 {
-  if (pool_is_free_index (segment_managers, index))
+  if (pool_is_free_index (segment_manager_main.segment_managers, index))
     return 0;
-  return pool_elt_at_index (segment_managers, index);
+  return pool_elt_at_index (segment_manager_main.segment_managers, index);
 }
 
 always_inline u32
 segment_manager_index (segment_manager_t * sm)
 {
-  return sm - segment_managers;
+  return sm - segment_manager_main.segment_managers;
+}
+
+always_inline svm_queue_t *
+segment_manager_event_queue (segment_manager_t * sm)
+{
+  return sm->event_queue;
 }
 
 segment_manager_t *segment_manager_new ();
-int segment_manager_init (segment_manager_t * sm, u32 props_index,
-			  u32 seg_size, u32 evt_queue_size);
+int segment_manager_init (segment_manager_t * sm, u32 first_seg_size,
+			  u32 evt_q_size, u32 prealloc_fifo_pairs);
+
+svm_fifo_segment_private_t *segment_manager_get_segment (segment_manager_t *
+							 sm,
+							 u32 segment_index);
+svm_fifo_segment_private_t
+  * segment_manager_get_segment_w_lock (segment_manager_t * sm,
+					u32 segment_index);
+void segment_manager_segment_reader_unlock (segment_manager_t * sm);
+void segment_manager_segment_writer_unlock (segment_manager_t * sm);
 
-svm_fifo_segment_private_t *segment_manager_get_segment (u32 segment_index);
 int segment_manager_add_first_segment (segment_manager_t * sm,
 				       u32 segment_size);
-int segment_manager_add_segment (segment_manager_t * sm);
 void segment_manager_del_sessions (segment_manager_t * sm);
 void segment_manager_del (segment_manager_t * sm);
 void segment_manager_init_del (segment_manager_t * sm);
@@ -117,10 +156,9 @@ svm_queue_t *segment_manager_alloc_queue (segment_manager_t * sm,
 void segment_manager_dealloc_queue (segment_manager_t * sm, svm_queue_t * q);
 void segment_manager_app_detach (segment_manager_t * sm);
 
-segment_manager_properties_t *segment_manager_properties_alloc (void);
-void segment_manager_properties_free (segment_manager_properties_t * p);
-segment_manager_properties_t *segment_manager_properties_get (u32 smp_index);
-u32 segment_manager_properties_index (segment_manager_properties_t * p);
+void segment_manager_main_init (segment_manager_main_init_args_t * a);
+segment_manager_properties_t
+  * segment_manager_properties_init (segment_manager_properties_t * sm);
 
 #endif /* SRC_VNET_SESSION_SEGMENT_MANAGER_H_ */
 /*
diff --git a/src/vnet/session/session.c b/src/vnet/session/session.c
index ae8c42aa32b..de3cbc57d66 100644
--- a/src/vnet/session/session.c
+++ b/src/vnet/session/session.c
@@ -1115,6 +1115,7 @@ listen_session_get_local_session_endpoint (stream_session_t * listener,
 static clib_error_t *
 session_manager_main_enable (vlib_main_t * vm)
 {
+  segment_manager_main_init_args_t _sm_args = { 0 }, *sm_args = &_sm_args;
   session_manager_main_t *smm = &session_manager_main;
   vlib_thread_main_t *vtm = vlib_get_thread_main ();
   u32 num_threads;
@@ -1162,8 +1163,9 @@ session_manager_main_enable (vlib_main_t * vm)
   session_vpp_event_queues_allocate (smm);
 
   /* Initialize fifo segment main baseva and timeout */
-  svm_fifo_segment_init (smm->session_baseva + smm->evt_qs_segment_size,
-			 smm->segment_timeout);
+  sm_args->baseva = smm->session_baseva + smm->evt_qs_segment_size;
+  sm_args->size = smm->session_va_space_size;
+  segment_manager_main_init (sm_args);
 
   /* Preallocate sessions */
   if (smm->preallocated_sessions)
@@ -1237,7 +1239,7 @@ session_manager_main_init (vlib_main_t * vm)
 {
   session_manager_main_t *smm = &session_manager_main;
   smm->session_baseva = 0x200000000ULL;
-  smm->segment_timeout = 20;
+  smm->session_va_space_size = (u64) 128 << 30;
   smm->evt_qs_segment_size = 64 << 20;
   smm->is_enabled = 0;
   return 0;
diff --git a/src/vnet/session/session.h b/src/vnet/session/session.h
index d0bf95c41e4..ec00e291721 100644
--- a/src/vnet/session/session.h
+++ b/src/vnet/session/session.h
@@ -70,7 +70,8 @@ _(FIFO_FULL, "Packets dropped for lack of rx fifo space")               \
 _(EVENT_FIFO_FULL, "Events not sent for lack of event fifo space")      \
 _(API_QUEUE_FULL, "Sessions not created for lack of API queue space")   \
 _(NEW_SEG_NO_SPACE, "Created segment, couldn't allocate a fifo pair")   \
-_(NO_SPACE, "Couldn't allocate a fifo pair")
+_(NO_SPACE, "Couldn't allocate a fifo pair")				\
+_(SEG_CREATE, "Couldn't create a new segment")
 
 typedef enum
 {
@@ -171,7 +172,7 @@ struct _session_manager_main
 
   /** Session ssvm segment configs*/
   uword session_baseva;
-  u32 segment_timeout;
+  uword session_va_space_size;
   u32 evt_qs_segment_size;
   u8 evt_qs_use_memfd_seg;
 
diff --git a/src/vnet/session/session_api.c b/src/vnet/session/session_api.c
index a1225f83e8c..57af960597d 100755
--- a/src/vnet/session/session_api.c
+++ b/src/vnet/session/session_api.c
@@ -290,7 +290,7 @@ redirect_connect_callback (u32 server_api_client_index, void *mp_arg)
       return -1;
     }
 
-  props = segment_manager_properties_get (app->sm_properties);
+  props = application_segment_manager_properties (app);
   mp->options[APP_OPTIONS_RX_FIFO_SIZE] = props->rx_fifo_size;
   mp->options[APP_OPTIONS_TX_FIFO_SIZE] = props->tx_fifo_size;
 
diff --git a/src/vnet/session/session_test.c b/src/vnet/session/session_test.c
index a9a902d27bc..febe1b7998a 100644
--- a/src/vnet/session/session_test.c
+++ b/src/vnet/session/session_test.c
@@ -99,6 +99,44 @@ static session_cb_vft_t dummy_session_cbs = {
 /* *INDENT-ON* */
 
 static int
+session_create_lookpback (u32 table_id, u32 * sw_if_index,
+			  ip4_address_t * intf_addr)
+{
+  u8 intf_mac[6];
+
+  memset (intf_mac, 0, sizeof (intf_mac));
+
+  if (vnet_create_loopback_interface (sw_if_index, intf_mac, 0, 0))
+    {
+      clib_warning ("couldn't create loopback. stopping the test!");
+      return -1;
+    }
+
+  if (table_id != 0)
+    ip_table_bind (FIB_PROTOCOL_IP4, *sw_if_index, table_id, 0);
+
+  vnet_sw_interface_set_flags (vnet_get_main (), *sw_if_index,
+			       VNET_SW_INTERFACE_FLAG_ADMIN_UP);
+
+  if (ip4_add_del_interface_address (vlib_get_main (), *sw_if_index,
+				     intf_addr, 24, 0))
+    {
+      clib_warning ("couldn't assign loopback ip %U", format_ip4_address,
+		    intf_addr);
+      return -1;
+    }
+
+  return 0;
+}
+
+static void
+session_delete_loopback (u32 sw_if_index)
+{
+  /* fails spectacularly  */
+  /* vnet_delete_loopback_interface (sw_if_index); */
+}
+
+static int
 session_test_basic (vlib_main_t * vm, unformat_input_t * input)
 {
   session_endpoint_t server_sep = SESSION_ENDPOINT_NULL;
@@ -174,7 +212,7 @@ session_test_namespace (vlib_main_t * vm, unformat_input_t * input)
   session_endpoint_t client_sep = SESSION_ENDPOINT_NULL;
   session_endpoint_t intf_sep = SESSION_ENDPOINT_NULL;
   clib_error_t *error = 0;
-  u8 *ns_id = format (0, "appns1"), intf_mac[6];
+  u8 *ns_id = format (0, "appns1");
   app_namespace_t *app_ns;
   application_t *server;
   stream_session_t *s;
@@ -185,7 +223,6 @@ session_test_namespace (vlib_main_t * vm, unformat_input_t * input)
   client_sep.is_ip4 = 1;
   client_sep.port = dummy_port;
   memset (options, 0, sizeof (options));
-  memset (intf_mac, 0, sizeof (intf_mac));
 
   options[APP_OPTIONS_FLAGS] = APP_OPTIONS_FLAGS_IS_BUILTIN;
   options[APP_OPTIONS_FLAGS] |= APP_OPTIONS_FLAGS_ACCEPT_REDIRECT;
@@ -440,15 +477,7 @@ session_test_namespace (vlib_main_t * vm, unformat_input_t * input)
   /*
    * Create loopback interface
    */
-  if (vnet_create_loopback_interface (&sw_if_index, intf_mac, 0, 0))
-    {
-      clib_warning ("couldn't create loopback. stopping the test!");
-      return 0;
-    }
-  vnet_sw_interface_set_flags (vnet_get_main (), sw_if_index,
-			       VNET_SW_INTERFACE_FLAG_ADMIN_UP);
-  ip4_add_del_interface_address (vlib_get_main (), sw_if_index, &intf_addr,
-				 24, 0);
+  session_create_lookpback (0, &sw_if_index, &intf_addr);
 
   /*
    * Update namespace
@@ -492,8 +521,7 @@ session_test_namespace (vlib_main_t * vm, unformat_input_t * input)
    * Cleanup
    */
   vec_free (ns_id);
-  /* fails in multi core scenarions .. */
-  /* vnet_delete_loopback_interface (sw_if_index); */
+  session_delete_loopback (sw_if_index);
   return 0;
 }
 
@@ -1014,8 +1042,6 @@ session_test_rules (vlib_main_t * vm, unformat_input_t * input)
 
   sep.ip.ip4.as_u32 -= 1 << 24;
 
-
-
   /*
    * Delete masking rule: 1.2.3.4/32 1234 5.6.7.8/32 4321 allow
    */
@@ -1337,7 +1363,7 @@ session_test_proxy (vlib_main_t * vm, unformat_input_t * input)
   u32 server_index, app_index;
   u32 dummy_server_api_index = ~0, sw_if_index = 0;
   clib_error_t *error = 0;
-  u8 intf_mac[6], sst, is_filtered = 0;
+  u8 sst, is_filtered = 0;
   stream_session_t *s;
   transport_connection_t *tc;
   u16 lcl_port = 1234, rmt_port = 4321;
@@ -1377,21 +1403,13 @@ session_test_proxy (vlib_main_t * vm, unformat_input_t * input)
   /*
    * Create loopback interface
    */
-  memset (intf_mac, 0, sizeof (intf_mac));
-  if (vnet_create_loopback_interface (&sw_if_index, intf_mac, 0, 0))
-    {
-      clib_warning ("couldn't create loopback. stopping the test!");
-      return 0;
-    }
-  vnet_sw_interface_set_flags (vnet_get_main (), sw_if_index,
-			       VNET_SW_INTERFACE_FLAG_ADMIN_UP);
-  ip4_add_del_interface_address (vlib_get_main (), sw_if_index, &lcl_ip,
-				 24, 0);
+  session_create_lookpback (0, &sw_if_index, &lcl_ip);
 
   app_ns = app_namespace_get_default ();
   app_ns->sw_if_index = sw_if_index;
 
   memset (options, 0, sizeof (options));
+  options[APP_OPTIONS_FLAGS] = APP_OPTIONS_FLAGS_IS_BUILTIN;
   options[APP_OPTIONS_FLAGS] |= APP_OPTIONS_FLAGS_ACCEPT_REDIRECT;
   options[APP_OPTIONS_FLAGS] |= APP_OPTIONS_FLAGS_IS_PROXY;
   options[APP_OPTIONS_PROXY_TRANSPORT] = 1 << TRANSPORT_PROTO_TCP;
diff --git a/src/vppinfra/lock.h b/src/vppinfra/lock.h
index 0ffb0455be0..dd79c40b7f2 100644
--- a/src/vppinfra/lock.h
+++ b/src/vppinfra/lock.h
@@ -109,6 +109,7 @@ typedef struct clib_rw_lock_
 {
   CLIB_CACHE_LINE_ALIGN_MARK (cacheline0);
   volatile u32 n_readers;
+  volatile u32 n_readers_lock;
   volatile u32 writer_lock;
 #if CLIB_DEBUG > 0
   pid_t pid;
@@ -137,23 +138,39 @@ clib_rwlock_free (clib_rwlock_t * p)
 always_inline void
 clib_rwlock_reader_lock (clib_rwlock_t * p)
 {
-  if (__sync_fetch_and_add (&(*p)->n_readers, 1) == 0)
+  while (__sync_lock_test_and_set (&(*p)->n_readers_lock, 1))
+    CLIB_PAUSE ();
+
+  (*p)->n_readers += 1;
+  if ((*p)->n_readers == 1)
     {
       while (__sync_lock_test_and_set (&(*p)->writer_lock, 1))
 	CLIB_PAUSE ();
     }
+  CLIB_MEMORY_BARRIER ();
+  (*p)->n_readers_lock = 0;
+
   CLIB_LOCK_DBG (p);
 }
 
 always_inline void
 clib_rwlock_reader_unlock (clib_rwlock_t * p)
 {
+  ASSERT ((*p)->n_readers > 0);
   CLIB_LOCK_DBG_CLEAR (p);
-  if (__sync_fetch_and_sub (&(*p)->n_readers, 1) == 1)
+
+  while (__sync_lock_test_and_set (&(*p)->n_readers_lock, 1))
+    CLIB_PAUSE ();
+
+  (*p)->n_readers -= 1;
+  if ((*p)->n_readers == 0)
     {
       CLIB_MEMORY_BARRIER ();
       (*p)->writer_lock = 0;
     }
+
+  CLIB_MEMORY_BARRIER ();
+  (*p)->n_readers_lock = 0;
 }
 
 always_inline void
diff --git a/test/test_session.py b/test/test_session.py
index 7219ffdc545..80e27c0a0e7 100644
--- a/test/test_session.py
+++ b/test/test_session.py
@@ -3,6 +3,7 @@
 import unittest
 
 from framework import VppTestCase, VppTestRunner
+from vpp_ip_route import VppIpTable, VppIpRoute, VppRoutePath
 
 
 class TestSession(VppTestCase):
@@ -15,7 +16,34 @@ class TestSession(VppTestCase):
     def setUp(self):
         super(TestSession, self).setUp()
 
+        self.vapi.session_enable_disable(is_enabled=1)
+        self.create_loopback_interfaces(range(2))
+
+        table_id = 0
+
+        for i in self.lo_interfaces:
+            i.admin_up()
+
+            if table_id != 0:
+                tbl = VppIpTable(self, table_id)
+                tbl.add_vpp_config()
+
+            i.set_table_ip4(table_id)
+            i.config_ip4()
+            table_id += 1
+
+        # Configure namespaces
+        self.vapi.app_namespace_add(namespace_id="0",
+                                    sw_if_index=self.loop0.sw_if_index)
+        self.vapi.app_namespace_add(namespace_id="1",
+                                    sw_if_index=self.loop1.sw_if_index)
+
     def tearDown(self):
+        for i in self.lo_interfaces:
+            i.unconfig_ip4()
+            i.set_table_ip4(0)
+            i.admin_down()
+
         super(TestSession, self).tearDown()
         self.vapi.session_enable_disable(is_enabled=1)
 
@@ -25,7 +53,41 @@ class TestSession(VppTestCase):
 
         if error:
             self.logger.critical(error)
-        self.assertEqual(error.find("Failed"), -1)
+        self.assertEqual(error.find("failed"), -1)
+
+    def test_segment_manager_alloc(self):
+        """ Session Segment Manager Multiple Segment Allocation """
+
+        # Add inter-table routes
+        ip_t01 = VppIpRoute(self, self.loop1.local_ip4, 32,
+                            [VppRoutePath("0.0.0.0",
+                                          0xffffffff,
+                                          nh_table_id=1)])
+        ip_t10 = VppIpRoute(self, self.loop0.local_ip4, 32,
+                            [VppRoutePath("0.0.0.0",
+                                          0xffffffff,
+                                          nh_table_id=0)], table_id=1)
+        ip_t01.add_vpp_config()
+        ip_t10.add_vpp_config()
+
+        # Start builtin server and client with small private segments
+        uri = "tcp://" + self.loop0.local_ip4 + "/1234"
+        error = self.vapi.cli("test echo server appns 0 fifo-size 64 " +
+                              "private-segment-size 1m uri " + uri)
+        if error:
+            self.logger.critical(error)
+            self.assertEqual(error.find("failed"), -1)
+
+        error = self.vapi.cli("test echo client nclients 100 appns 1 " +
+                              "no-output fifo-size 64 syn-timeout 2 " +
+                              "private-segment-size 1m uri " + uri)
+        if error:
+            self.logger.critical(error)
+            self.assertEqual(error.find("failed"), -1)
+
+        # Delete inter-table routes
+        ip_t01.remove_vpp_config()
+        ip_t10.remove_vpp_config()
 
 if __name__ == '__main__':
     unittest.main(testRunner=VppTestRunner)