MultiCompiler didn't release memory after one compiler is finished.

Bug report

What is the current behavior? I use MultiCompiler configs.
If i run them one by one, Webpack can build them all.

const config = {}
webpack(config)

If i run them together, OOM appeares.

const configs = [config1, config2, config3, config4]
webpack(configs)

If the current behavior is a bug, please provide the steps to reproduce. MultiCompiler uses more memory than single compiler.

What is the expected behavior? Each compiler should work separately. when one is finished, who’s memory should be released.

Other relevant information: webpack version: 5.70.0 Node.js version: 14.17.1 Operating System: macOS 11.6 Additional tools: none

Part of configuration entries (each compiler): 2 + 159 + 230 cache: dsiabled mode: ‘production’ loaders: babel / postcss / vue-laoder minimizer: terser / css-minimizer-webpack-plugin devtool: false target: [‘web’, ‘es5’]

[vankop]

first of all we need to solve memory leak issue with module graph… otherwise all modules will be in this WeakMap until compiler. _cleanupLastCompilation will not be called…

[VisonM]

first of all we need to solve memory leak issue with module graph… otherwise all modules will be in this WeakMap until compiler. _cleanupLastCompilation will not be called…

the same problem we have too. I record mutli times momory useage in chrome devtool after compiler.close trigger.