tx clement

this is indeed really important

On Fri, 03 Mar 2017 11:56:05 +0100, Cl��ment Bera <bera.clement@gmail.com> wrote:

Hello everyone,

This morning I investigated with Vincent Blondeau a problem reported by the Moose community a while ago: loading Moose model is slower in Spur (Pharo 5+) than in pre-Spur (Pharo 4 and older). In general, this problem was present for anyone growing images to a significant size.

To investigate the problem, we loaded a 200Mb[3] Moose model on a 250Mb image, growing the image to 450Mb. Loading such a model takes 2 minutes in Spur and 1m30s in pre-Spur VMs.

Using the stable Pharo VM, the analysis results were the following:

- total time spent to load the Model: 2 minutes

- time spent in full GC: 1 minute (4 fullGCs)

- time spent in scavenges[1]: 15 seconds

On the 2 minutes spent, we have 50% of the time spent in full GCs, 12.5% in scavenges, 37.5% executing code.

We then used the latest VM that features the new compactor (VM from beginning of March 2017 and over). The full GC execution time went down from 1 minute to 2 seconds.

In addition, we increased the size of Eden[2] from 4Mb to 12Mb. Time spent in scavenges decreased from 15 seconds to 5 seconds.

Overall, loading the model is now taking ~50 seconds instead of 2 minutes.

To increase Eden size, one needs to run a script similar to:

| currentEdenSize desiredEdenSize |

currentEdenSize := Smalltalk vm parameterAt: 44.

desiredEdenSize := currentEdenSize * 4.

Smalltalk vm parameterAt: 45 put: desiredEdenSize.

And then restart the image.

I hope this report can be useful for some of you. I will try to make a blog post out of it, detailing other GC settings one can change from the image to improve performance.

Best,

Clement

[1] A scavenge is basically the garbage collection of only young objects

[2] Eden is basically the space where objects are initially allocated.

[3] All numbers in the report are order of magnitudes and not precise numbers

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