allocate swap size for containers based on system ratio

src/docker.js

@@ -45,6 +45,7 @@ var addons = require('./addons.js'),
     settings = require('./settings.js'),
     shell = require('./shell.js'),
     safe = require('safetydance'),
+    system = require('./system.js'),
     util = require('util'),
     volumes = require('./volumes.js'),
     _ = require('underscore');
@@ -313,7 +314,7 @@ function createSubcontainer(app, name, cmd, options, callback) {
                             'syslog-format': 'rfc5424'
                         }
                     },
-                    Memory: memoryLimit / 2,
+                    Memory: system.getMemoryAllocation(memoryLimit),
                     MemorySwap: memoryLimit, // Memory + Swap
                     PortBindings: isAppContainer ? dockerPortBindings : { },
                     PublishAllPorts: false,