From: Eric Dumazet <eric.dumazet@gmail.com> Date: Thu, 04 Jul 2013 03:12:10 -0700> It looks like a typical COW issue to me.Generically speaking, if we have to mess with page protections this eliminates the performance gain from bypass/zerocopy/whatever that these virtualization layers are doing. But there may be other factors involved which might mitigate that.