Implement trim() for command pools

vulkano/src/command_buffer/pool/sys.rs

@@ -106,6 +106,19 @@ impl UnsafeCommandPool {
         Ok(())
     }
 
+    /// Trims a command pool, which recycles unused internal memory from the command pool back to the system.
+    ///
+    /// Command buffers allocated from the pool are not affected by trimming.
+    #[inline]
+    pub fn trim(&self) -> () {
+        assert!(self.device.loaded_extensions().khr_maintenance1); //TODO return error?
+        unsafe {
+            let flags = 0;
+            let vk = self.device.pointers();
+            vk.TrimCommandPoolKHR(self.device.internal_object(), self.pool, flags);
+        }
+    }
+
     /// Allocates `count` command buffers.
     ///
     /// If `secondary` is true, allocates secondary command buffers. Otherwise, allocates primary

vulkano/src/instance/extensions.rs

@@ -210,6 +210,7 @@ device_extensions! {
     khr_swapchain => b"VK_KHR_swapchain",
     khr_display_swapchain => b"VK_KHR_display_swapchain",
     khr_sampler_mirror_clamp_to_edge => b"VK_KHR_sampler_mirror_clamp_to_edge",
+    khr_maintenance1 => b"VK_KHR_maintenance1",
 }
 
 /// Error that can happen when loading the list of layers.