Server GC mode for compiler

[latkin]

As mentioned in #404.

I don't think we should change fsi/fsianycpu, as those are sometimes used to drive interactive UIs, which benefit from the increased responsiveness of the default GC.

[KevinRansom]

Unfortunately, the exact same change will need to be made in the internal build. But the improvements look very desirable.

Looks good to me.

[enricosada]

@latkin can you try with gcConcurrent = false?

note on gcServer msdn

In the .NET Framework 4 and earlier versions, concurrent garbage collection is not available when server garbage collection is enabled. Starting with the .NET Framework 4.5, server garbage collection is concurrent. To use non-concurrent server garbage collection, set the element to true and the element to false

the gcConcurrent msdn :

By default, the runtime uses concurrent or background garbage collection, which is optimized for latency. If your application involves heavy user interaction, leave concurrent garbage collection enabled to minimize the application's pause time to perform garbage collection. If you set the enabled attribute of the element to false, the runtime uses non-concurrent garbage collection, which is optimized for throughput. The following configuration file disables background garbage collection

[latkin]

@enricosada I looked at that, but it actually does not apply, due to our use of GCLatencyMode.Batch. Per docs:

This mode overrides the runtime configuration setting. If is enabled, switching to Batch mode prevents any further concurrent collections.

[enricosada]

ah ok, nice to know. I saw the docs , and was worth a try to ask for it.

[latkin]

I will leave a short comment so that if Batch mode is ever changed/removed, developer will know to investigate gcConcurrent. Thanks for the reminder.