allocate swap size for containers based on system ratio

src/addons.js

@@ -59,6 +59,7 @@ var appdb = require('./appdb.js'),
     spawn = require('child_process').spawn,
     split = require('split'),
     request = require('request'),
+    system = require('./system.js'),
     util = require('util');
 
 const NOOP = function (app, options, callback) { return callback(); };
@@ -811,7 +812,7 @@ function updateServiceConfig(platformConfig, callback) {
         const containerConfig = platformConfig[serviceName];
         let memory, memorySwap;
         if (containerConfig && containerConfig.memoryLimit) {
-            memory = containerConfig.memoryLimit / 2;
+            memory = system.getMemoryAllocation(containerConfig.memoryLimit);
             memorySwap = containerConfig.memoryLimit;
         } else {
             memory = SERVICES[serviceName].defaultMemoryLimit;
@@ -838,7 +839,7 @@ function updateAppServiceConfig(name, instance, servicesConfig, callback) {
     const serviceConfig = servicesConfig[name];
     let memory, memorySwap;
     if (serviceConfig && serviceConfig.memoryLimit) {
-        memory = serviceConfig.memoryLimit / 2;
+        memory = system.getMemoryAllocation(serviceConfig.memoryLimit);
         memorySwap = serviceConfig.memoryLimit;
     } else {
         memory = APP_SERVICES[name].defaultMemoryLimit;

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,

src/system.js

@@ -3,7 +3,8 @@
 exports = module.exports = {
     getDisks,
     checkDiskSpace,
-    getMemory
+    getMemory,
+    getMemoryAllocation
 };
 
 const apps = require('./apps.js'),
@@ -148,14 +149,24 @@ function checkDiskSpace(callback) {
     });
 }
 
-function getMemory(callback) {
-    assert.strictEqual(typeof callback, 'function');
-
+function getSwapSize() {
     const stdout = safe.child_process.execSync('swapon --noheadings --raw --bytes --show=SIZE', { encoding: 'utf8' });
     const swap = !stdout ? 0 : stdout.trim().split('\n').map(x => parseInt(x, 10) || 0).reduce((acc, cur) => acc + cur);
 
+    return swap;
+}
+
+function getMemory(callback) {
+    assert.strictEqual(typeof callback, 'function');
+
     callback(null, {
         memory: os.totalmem(),
-        swap: swap
+        swap: getSwapSize()
     });
 }
+
+function getMemoryAllocation(limit) {
+    const pc = os.totalmem() / (os.totalmem() + getSwapSize());
+    const ratio = Math.round(pc * 10) / 10; // a simple ratio
+    return Math.round(Math.round(limit * ratio) / 1048576) * 1048576; // nearest MB
+}