diff --git a/vlib/builtin/builtin.v b/vlib/builtin/builtin.v
index 7cbcb6fb1f..22e6bb6bb7 100644
--- a/vlib/builtin/builtin.v
+++ b/vlib/builtin/builtin.v
@@ -136,6 +136,7 @@ pub fn malloc(n int) byteptr {
 		panic('malloc(<=0)')
 	}
 	$if prealloc {
+		//println('p')
 		res := g_m2_ptr
 		unsafe {
 			g_m2_ptr += n
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 2374316c74..ae4a8d74fc 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -15,8 +15,8 @@ import v.depgraph
 const (
 	c_reserved = ['delete', 'exit', 'link', 'unix', 'error', 'calloc', 'malloc', 'free', 'panic',
 		'auto', 'char', 'default', 'do', 'double', 'extern', 'float', 'inline', 'int', 'long', 'register',
-		'restrict', 'short', 'signed', 'sizeof', 'static', 'switch', 'typedef', 'union', 'unsigned',
-		'void', 'volatile', 'while', 'new', 'namespace', 'class', 'typename']
+		'restrict', 'short', 'signed', 'sizeof', 'static', 'switch', 'typedef', 'union', 'unsigned', 'void',
+		'volatile', 'while', 'new', 'namespace', 'class', 'typename']
 	// same order as in token.Kind
 	cmp_str    = ['eq', 'ne', 'gt', 'lt', 'ge', 'le']
 	// when operands are switched
@@ -286,6 +286,9 @@ pub fn (mut g Gen) init() {
 		g.comptime_defines.writeln('#define _VAUTOFREE (1)')
 		// g.comptime_defines.writeln('unsigned char* g_cur_str;')
 	}
+	if g.pref.prealloc {
+		g.comptime_defines.writeln('#define _VPREALLOC (1)')
+	}
 	if g.pref.is_livemain || g.pref.is_liveshared {
 		g.generate_hotcode_reloading_declarations()
 	}
@@ -409,7 +412,7 @@ fn (mut g Gen) register_optional(t table.Type) string {
 }
 
 fn (mut g Gen) find_or_register_shared(t table.Type, base string) string {
-	sh_typ :=  '__shared__$base'
+	sh_typ := '__shared__$base'
 	t_idx := t.idx()
 	if t_idx in g.shareds {
 		return sh_typ
@@ -968,13 +971,11 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type, expected_type table.Type)
 				g.write('/* sum type cast */ ($exp_styp) {.obj = ')
 				g.expr(expr)
 				g.write(', .typ = $got_idx /* $got_sym.name */}')
-			}
-			else {
+			} else {
 				g.write('/* sum type cast */ ($exp_styp) {.obj = memdup(&($got_styp[]) {')
 				g.expr(expr)
 				g.write('}, sizeof($got_styp)), .typ = $got_idx /* $got_sym.name */}')
 			}
-
 			return
 		}
 	}
@@ -1073,16 +1074,30 @@ fn (mut g Gen) gen_assert_metainfo(a ast.AssertStmt) string {
 fn (mut g Gen) gen_assert_single_expr(e ast.Expr, t table.Type) {
 	unknown_value := '*unknown value*'
 	match e {
-		ast.CallExpr { g.write(ctoslit(unknown_value)) }
-		ast.CastExpr { g.write(ctoslit(unknown_value)) }
-		ast.IndexExpr { g.write(ctoslit(unknown_value)) }
-		ast.PrefixExpr { g.write(ctoslit(unknown_value)) }
-		ast.MatchExpr { g.write(ctoslit(unknown_value)) }
+		ast.CallExpr {
+			g.write(ctoslit(unknown_value))
+		}
+		ast.CastExpr {
+			g.write(ctoslit(unknown_value))
+		}
+		ast.IndexExpr {
+			g.write(ctoslit(unknown_value))
+		}
+		ast.PrefixExpr {
+			g.write(ctoslit(unknown_value))
+		}
+		ast.MatchExpr {
+			g.write(ctoslit(unknown_value))
+		}
 		ast.Type {
 			sym := g.table.get_type_symbol(t)
 			g.write(ctoslit('$sym.name'))
 		}
-		else { g.gen_expr_to_string(e, t) or { g.write(ctoslit('[$err]')) } }
+		else {
+			g.gen_expr_to_string(e, t) or {
+				g.write(ctoslit('[$err]'))
+			}
+		}
 	}
 	g.write(' /* typeof: ' + typeof(e) + ' type: ' + t.str() + ' */ ')
 }
@@ -1152,14 +1167,13 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 						arg_len := func.func.args.len
 						for j, arg in func.func.args {
 							arg_type := g.table.get_type_symbol(arg.typ)
-							g.write('${arg_type.str()} ${arg.name}')
+							g.write('$arg_type.str() $arg.name')
 							if j < arg_len - 1 {
 								g.write(', ')
 							}
 						}
 						g.writeln(') = $left.name;')
-					}
-					else {
+					} else {
 						styp := g.typ(var_type)
 						g.writeln('$styp _var_$left.pos.pos = $left.name;')
 					}
@@ -1240,7 +1254,7 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 				is_call = true
 				return_type = val.return_type
 			}
-				// TODO: no buffer fiddling
+			// TODO: no buffer fiddling
 			ast.AnonFn {
 				if blank_assign {
 					g.write('{')
@@ -2112,16 +2126,16 @@ fn (mut g Gen) lock_expr(node ast.LockExpr) {
 		deref := if id.is_mut { '->' } else { '.' }
 		lock_prefix := if node.is_rlock { `r` } else { `w` }
 		lock_prefixes << lock_prefix // keep for unlock
-		g.writeln('sync__RwMutex_${lock_prefix:c}_lock(${name}${deref}mtx);')
+		g.writeln('sync__RwMutex_${lock_prefix:c}_lock($name${deref}mtx);')
 	}
 	g.stmts(node.stmts)
 	// unlock in reverse order
-	for i := node.lockeds.len-1; i >= 0; i-- {
+	for i := node.lockeds.len - 1; i >= 0; i-- {
 		id := node.lockeds[i]
 		lock_prefix := lock_prefixes[i]
 		name := id.name
 		deref := if id.is_mut { '->' } else { '.' }
-		g.writeln('sync__RwMutex_${lock_prefix:c}_unlock(${name}${deref}mtx);')
+		g.writeln('sync__RwMutex_${lock_prefix:c}_unlock($name${deref}mtx);')
 	}
 }
 
@@ -2863,7 +2877,9 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 		fields = struct_init.fields
 	}
 	*/
-	if is_multiline { g.indent++ }
+	if is_multiline {
+		g.indent++
+	}
 	// User set fields
 	mut initialized := false
 	for i, field in struct_init.fields {
@@ -2929,7 +2945,6 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 				} else {
 					g.write(',')
 				}
-
 				initialized = true
 				continue
 			}
@@ -2947,11 +2962,12 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 			} else {
 				g.write(',')
 			}
-
 			initialized = true
 		}
 	}
-	if is_multiline { g.indent-- }
+	if is_multiline {
+		g.indent--
+	}
 	// if struct_init.fields.len == 0 && info.fields.len == 0 {
 	if !initialized {
 		g.write('\n#ifndef __cplusplus\n0\n#endif\n')
@@ -3105,6 +3121,10 @@ fn (mut g Gen) write_init_function() {
 		// mb_size := if s_str_buf_size == '' { 1 } else { s_str_buf_size.int() }
 		// g.writeln('g_str_buf = malloc( ${mb_size} * 1024 * 1000 );')
 	}
+	if g.pref.prealloc {
+		g.writeln('g_m2_buf = malloc(50 * 1000 * 1000);')
+		g.writeln('g_m2_ptr = g_m2_buf;')
+	}
 	g.writeln('\tbuiltin_init();')
 	g.writeln('\tvinit_string_literals();')
 	//
@@ -3297,7 +3317,7 @@ fn (g Gen) sort_structs(typesa []table.TypeSymbol) []table.TypeSymbol {
 					field_deps << dep
 				}
 			}
-				// table.Interface {}
+			// table.Interface {}
 			else {}
 		}
 		// add type and dependant types to graph
@@ -3757,11 +3777,11 @@ fn (mut g Gen) comp_if_to_ifdef(name string, is_comptime_optional bool) string {
 		'linux_or_macos' {
 			return ''
 		}
-			//
+		//
 		'js' {
 			return '_VJS'
 		}
-			// compilers:
+		// compilers:
 		'tinyc' {
 			return '__TINYC__'
 		}
@@ -3777,7 +3797,7 @@ fn (mut g Gen) comp_if_to_ifdef(name string, is_comptime_optional bool) string {
 		'cplusplus' {
 			return '__cplusplus'
 		}
-			// other:
+		// other:
 		'debug' {
 			return '_VDEBUG'
 		}
@@ -3788,7 +3808,7 @@ fn (mut g Gen) comp_if_to_ifdef(name string, is_comptime_optional bool) string {
 			return '__GLIBC__'
 		}
 		'prealloc' {
-			return 'VPREALLOC'
+			return '_VPREALLOC'
 		}
 		'no_bounds_checking' {
 			return 'CUSTOM_DEFINE_no_bounds_checking'
@@ -4174,7 +4194,7 @@ fn (mut g Gen) gen_str_for_enum(info table.Enum, styp, str_fn_name string) {
 	g.auto_str_funcs.writeln('string ${str_fn_name}($styp it) { /* gen_str_for_enum */')
 	g.auto_str_funcs.writeln('\tswitch(it) {')
 	// Only use the first multi value on the lookup
-	mut seen := []string{len:info.vals.len}
+	mut seen := []string{len: info.vals.len}
 	for val in info.vals {
 		if info.is_multi_allowed && val in seen {
 			continue
@@ -4246,7 +4266,7 @@ fn (mut g Gen) gen_str_for_struct(info table.Struct, styp, str_fn_name string) {
 				g.auto_str_funcs.write('indents, ')
 				if has_custom_str {
 					g.auto_str_funcs.write('${field_styp_fn_name}( it->${c_name(field.name)} ) ')
-				}else{
+				} else {
 					g.auto_str_funcs.write('indent_${field_styp_fn_name}( it->${c_name(field.name)}, indent_count + 1 ) ')
 				}
 			} else if sym.kind in [.array, .array_fixed, .map] {
diff --git a/vlib/v/pref/pref.v b/vlib/v/pref/pref.v
index e03c4230f4..e3a31708b3 100644
--- a/vlib/v/pref/pref.v
+++ b/vlib/v/pref/pref.v
@@ -195,6 +195,9 @@ pub fn parse_args(args []string) (&Preferences, string) {
 			'-usecache' {
 				res.use_cache = true
 			}
+			'-prealloc' {
+				res.prealloc = true
+			}
 			'-keepc' {
 				eprintln('-keepc is deprecated. V always keeps the generated .tmp.c files now.')
 			}