Mojo EDK: Reduce unused read buffer capacity

mojo/edk/system/channel.cc

Index: mojo/edk/system/channel.cc
diff --git a/mojo/edk/system/channel.cc b/mojo/edk/system/channel.cc
index a020ee6b482aed85a23f084abd27edf689240472..1621bbfe15da813d2bdcd82c8affd0a46a78fdde 100644
--- a/mojo/edk/system/channel.cc
+++ b/mojo/edk/system/channel.cc
@@ -37,7 +37,7 @@ static_assert(sizeof(Channel::Message::Header) == 8,
 }  // namespace
 
 const size_t kReadBufferSize = 4096;
-const size_t kMaxUnusedReadBufferCapacity = 64 * 1024;
+const size_t kMaxUnusedReadBufferCapacity = 4096;
 const size_t kMaxChannelMessageSize = 256 * 1024 * 1024;
 const size_t kMaxAttachedHandles = 128;