tx clement
this is indeed really important
On Fri, 03 Mar 2017 11:56:05 +0100, Clément Bera <[email protected]>
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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