add option "populate_io_buffers"

Author: MaxKellermann

debian/changelog

@@ -1,5 +1,6 @@
 cm4all-myproxy (0.30) unstable; urgency=low
 
+  * add option "populate_io_buffers"
   * fix build with glibc 2.43
 
  --   

doc/index.rst

@@ -69,6 +69,14 @@ means they must not do any network I/O, launch child processes, and
 should avoid anything but querying the parameters.
 
 
+Global Variables
+^^^^^^^^^^^^^^^^
+
+- ``populate_io_buffers``: ``true`` populates all I/O buffers on
+  startup.  This reduces waits for Linux kernel VM
+  compaction/migration.
+
+
 Control Listener
 ----------------
 

src/Main.cxx

@@ -23,6 +23,7 @@
 #include "lua/io/CgroupInfo.hxx"
 #include "lib/fmt/RuntimeError.hxx"
 #include "lib/fmt/SystemError.hxx"
+#include "memory/SlicePool.hxx"
 #include "net/AllocatedSocketAddress.hxx"
 #include "net/LocalSocketAddress.hxx"
 #include "net/Parser.hxx"
@@ -81,6 +82,15 @@ IsSystemdMagic(lua_State *L, int idx)
 
 #endif // HAVE_LIBSYSTEMD
 
+static bool
+GetGlobalBool(lua_State *L, const char *name)
+{
+	lua_getglobal(L, name);
+	AtScopeExit(L) { lua_pop(L, 1); };
+
+	return lua_toboolean(L, -1);
+}
+
 static auto
 ParameterToLuaHandler(lua_State *L, int idx)
 try {
@@ -291,6 +301,9 @@ try {
 		return EX_CONFIG;
 	}
 
+	if (GetGlobalBool(instance.GetLuaState(), "populate_io_buffers"))
+		fb_pool_get().Populate();
+
 	SetupRuntimeState(instance.GetLuaState());
 
 #ifdef HAVE_LIBSYSTEMD