dmabuf: share the mapping with shared copies of the memory

With lots of shared memory instances (e.g. created by a RTP payloader) the
overhead of duplicating the file descriptor and creating extra mappings is
significant. To avoid this, the parent memory maps the whole region and the
shared copies just reuse the same mapping.

https://bugzilla.gnome.org/show_bug.cgi?id=730441

diff --git a/gst-libs/gst/allocators/gstdmabuf.c b/gst-libs/gst/allocators/gstdmabuf.c
index f3b3efd..046b38b 100644 (file)
--- a/gst-libs/gst/allocators/gstdmabuf.c
+++ b/gst-libs/gst/allocators/gstdmabuf.c
@@ -53,7 +53,6 @@ typedef struct
   gpointer data;
   gint mmapping_flags;
   gint mmap_count;
-  gsize mmap_size;
   GMutex lock;
 } GstDmaBufMemory;
 
@@ -68,9 +67,10 @@ gst_dmabuf_allocator_free (GstAllocator * allocator, GstMemory * gmem)
 
   if (mem->data) {
     g_warning (G_STRLOC ":%s: Freeing memory %p still mapped", G_STRFUNC, mem);
-    munmap ((void *) mem->data, mem->mmap_size);
+    munmap ((void *) mem->data, gmem->maxsize);
   }
-  close (mem->fd);
+  if (mem->fd >= 0)
+    close (mem->fd);
   g_mutex_clear (&mem->lock);
   g_slice_free (GstDmaBufMemory, mem);
   GST_DEBUG ("%p: freed", mem);
@@ -85,6 +85,9 @@ gst_dmabuf_mem_map (GstMemory * gmem, gsize maxsize, GstMapFlags flags)
   gint prot;
   gpointer ret = NULL;
 
+  if (gmem->parent)
+    return gst_dmabuf_mem_map (gmem->parent, maxsize, flags);
+
   g_mutex_lock (&mem->lock);
 
   prot = flags & GST_MAP_READ ? PROT_READ : 0;
@@ -94,7 +97,7 @@ gst_dmabuf_mem_map (GstMemory * gmem, gsize maxsize, GstMapFlags flags)
   if (mem->data) {
     /* only return address if mapping flags are a subset
      * of the previous flags */
-    if ((mem->mmapping_flags & prot) && (mem->mmap_size >= maxsize)) {
+    if (mem->mmapping_flags & prot) {
       ret = mem->data;
       mem->mmap_count++;
     }
@@ -103,7 +106,7 @@ gst_dmabuf_mem_map (GstMemory * gmem, gsize maxsize, GstMapFlags flags)
   }
 
   if (mem->fd != -1) {
-    mem->data = mmap (0, maxsize, prot, MAP_SHARED, mem->fd, 0);
+    mem->data = mmap (0, gmem->maxsize, prot, MAP_SHARED, mem->fd, 0);
     if (mem->data == MAP_FAILED) {
       mem->data = NULL;
       GST_ERROR ("%p: fd %d: mmap failed: %s", mem, mem->fd,
@@ -116,7 +119,6 @@ gst_dmabuf_mem_map (GstMemory * gmem, gsize maxsize, GstMapFlags flags)
 
   if (mem->data) {
     mem->mmapping_flags = prot;
-    mem->mmap_size = maxsize;
     mem->mmap_count++;
     ret = mem->data;
   }
@@ -134,12 +136,15 @@ gst_dmabuf_mem_unmap (GstMemory * gmem)
 {
 #ifdef HAVE_MMAP
   GstDmaBufMemory *mem = (GstDmaBufMemory *) gmem;
+
+  if (gmem->parent)
+    return gst_dmabuf_mem_unmap (gmem->parent);
+
   g_mutex_lock (&mem->lock);
 
   if (mem->data && !(--mem->mmap_count)) {
-    munmap ((void *) mem->data, mem->mmap_size);
+    munmap ((void *) mem->data, gmem->maxsize);
     mem->data = NULL;
-    mem->mmap_size = 0;
     mem->mmapping_flags = 0;
     GST_DEBUG ("%p: fd %d unmapped", mem, mem->fd);
   }
@@ -171,7 +176,7 @@ gst_dmabuf_mem_share (GstMemory * gmem, gssize offset, gssize size)
       GST_MINI_OBJECT_FLAG_LOCK_READONLY, mem->mem.allocator, parent,
       mem->mem.maxsize, mem->mem.align, mem->mem.offset + offset, size);
 
-  sub->fd = dup (mem->fd);
+  sub->fd = -1;
   g_mutex_init (&sub->lock);
 
   return GST_MEMORY_CAST (sub);