background: Call malloc_trim() after loading background image

Some of the new JXL backgrounds from gnome-backgrounds can allocate
several hundred MB during loading, so let's call malloc_trim() after we
are done with loading the image into a pixbuf.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/3327
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3653>

src/compositor/meta-background-image.c

@@ -23,6 +23,10 @@
 #include <gdk-pixbuf/gdk-pixbuf.h>
 #include <gio/gio.h>
 
+#ifdef HAVE_MALLOC_TRIM
+#include <malloc.h>
+#endif
+
 #include "clutter/clutter.h"
 #include "compositor/cogl-utils.h"
 
@@ -135,6 +139,10 @@ load_file (GTask               *task,
   pixbuf = gdk_pixbuf_new_from_stream (G_INPUT_STREAM (stream), NULL, &error);
   g_object_unref (stream);
 
+#ifdef HAVE_MALLOC_TRIM
+  malloc_trim (0);
+#endif
+
   if (pixbuf == NULL)
     {
       g_task_return_error (task, error);