[Pharo-project] Memory profiling

Adrian Lienhard adi at netstyle.ch
Mon Apr 25 21:38:23 CEST 2011


Hi Alex,

I assume that your test run always creates the same number objects with the same size. Given that, there doesn't appear to be any reason why the amount of allocated memory for the given run should vary. So its rather the way you measure that makes the difference. I don't know how you get your profiles, but if you use the VM GC stats, they are global and hence other processes may influence the outcome.

Incremental GC is triggered depending on allocation count. There's a r/w VM param to configure this. So iGC is rather a crude way to measure memory usage as it doesn't consider object size (and it is a global counter)...

As a solution I suggest to take a look at my DTrace provider for the Squeak/Pharo VM [1]. It allows you to take statistics on questions like: how many instances of which size and of which class were created by which process in which methods? In the blog post I give an example that illustrates the use of DTrace for exactly such a question.

HTH,
Adrian

[1] http://www.adrian-lienhard.ch/blog?dialog=smalltak-meets-dtrace

 
On Apr 24, 2011, at 05:32 , Alexandre Bergel wrote:

> Hi!
> 
> I have been working on a memory profiler for Pharo. People who attended Smalltalks'10 may remember Mariano Coca's presentation.
> 
> Unfortunately, I am not satisfied with what we can obtain from the execution of a piece of code in Pharo. The amount of memory consumed by a method _significantly varies_ across execution. I have the impression that memory consumption is a less stable metric than execution time. 
> 
> For example, I used this as a benchmark:
> 
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> 	7 timesRepeat:   [
> 		5 timesRepeat: [  Smalltalk garbageCollect].
> 		MemoryProfiler
> 			viewProfiling: [ 
> 				20 timesRepeat:  [| view |
> 					5 timesRepeat: [  Smalltalk garbageCollect].
> 					Object new. Object new.
> 					5 timesRepeat: [  Smalltalk garbageCollect].
> 					
> 					view := MOViewRenderer new.
> 					view nodes: (1 to: 5000).
> 					view root applyLayout] ]
> 			inPackagesMatching: 'Mondrian-*'
> 			]
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> It opens a simple visualization in Mondrian. I tried to clean as much as I can before executing the code with multiple garbage collect.
> 
> This piece of code return 7 profiles.
> In a profile I have for the method MOBoundedShape>>heightFor: :
> Number of Young Allocated Bytes: 42,879,008 bytes
> Number of Old Allocated Bytes: 6,000,660 bytes
> Total Allocated Bytes: 48,879,668 bytes
> Number of Increased Memory Bytes: 0 bytes
> Number of Incremental GC's: 1,415
> Number of Full GC's: 0
> Number of Tenures of Surving Objects: 164
> 
> In another profile I have:
> Number of Young Allocated Bytes: -7,857,156 bytes
> Number of Old Allocated Bytes: 6,008,872 bytes
> Total Allocated Bytes: -1,848,284 bytes
> Number of Increased Memory Bytes: 0 bytes
> Number of Incremental GC's: 1,373
> Number of Full GC's: 0
> Number of Tenures of Surving Objects: 165
> 
> In another:
> Number of Young Allocated Bytes: -11,956,720 bytes
> Number of Old Allocated Bytes: 5,315,216 bytes
> Total Allocated Bytes: -6,641,504 bytes
> Number of Increased Memory Bytes: 0 bytes
> Number of Incremental GC's: 1,354
> Number of Full GC's: 0
> Number of Tenures of Surving Objects: 145
> 
> And another:
> Number of Young Allocated Bytes: 59,132,472 bytes
> Number of Old Allocated Bytes: 6,177,772 bytes
> Total Allocated Bytes: 65,310,244 bytes
> Number of Increased Memory Bytes: 0 bytes
> Number of Incremental GC's: 1,361
> Number of Full GC's: 0
> Number of Tenures of Surving Objects: 167
> 
> The metric "Number of Young Allocated Bytes", "Number of Old Allocated Bytes", "Total Allocated Bytes" are highly unpredictable: i.e., two profiles are likely to be completely different. I am not sure why is this so. I use the standard Pharo1.2 One click, without additional parameter to the VM. Do you think that other platforms and languages behave the same? 
> 
> However, the positive point is that it seems that the amount of incremental GC and the number of tenured objects may play an important role in estimating the memory consumption. These metrics are much more stable. 
> What do you think on this? Does it make sense to say that more a method triggers incremental GC, more it consumes memory? 
> 
> What exactly triggers an incremental GC? 
> 
> Cheers,
> Alexandre
> -- 
> _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
> Alexandre Bergel  http://www.bergel.eu
> ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
> 
> 
> 
> 
> 
> 




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