From 3c13aa178b007cae19800579b40e82bef127f388 Mon Sep 17 00:00:00 2001
From: Shawn Landden <shawn@git.icu>
Date: Tue, 9 Apr 2019 10:48:09 -0500
Subject: [PATCH] std.heap: do not excessively call mmap, and munmap in direct
 allocator

---
 std/heap.zig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/std/heap.zig b/std/heap.zig
index 239a65961a..bb2cd4f4d8 100644
--- a/std/heap.zig
+++ b/std/heap.zig
@@ -59,6 +59,8 @@ pub const DirectAllocator = struct {
 
     fn alloc(allocator: *Allocator, n: usize, alignment: u29) error{OutOfMemory}![]u8 {
         const self = @fieldParentPtr(DirectAllocator, "allocator", allocator);
+        if (n == 0)
+            return (([*]u8)(undefined))[0..0];
 
         switch (builtin.os) {
             Os.linux, Os.macosx, Os.ios, Os.freebsd, Os.netbsd => {
@@ -140,7 +142,9 @@ pub const DirectAllocator = struct {
                 }
                 const result = try alloc(allocator, new_size, new_align);
                 @memcpy(result.ptr, old_mem.ptr, std.math.min(old_mem.len, result.len));
-                _ = os.posix.munmap(@ptrToInt(old_mem.ptr), old_mem.len);
+                if (old_mem.len > 0) {
+                  _ = os.posix.munmap(@ptrToInt(old_mem.ptr), old_mem.len);
+                }
                 return result;
             },
             Os.windows => {