Re: [Squeak-VMdev] Re: GC improvements

[John M M. <jo...@ma...>]

On Jan 28, 2005, at 2:55 PM, Andreas Raab wrote:

> Hi John,
>
>> Ok, I consolidated all of this, added a prim to turn the biasGrowth  
>> behavior on where the grow and post fullGC logic is in the interp.c   
>> code, versus being partially in the image. Also a prim to set the   
>> threshold for doing the fullGC if we have grown by N bytes. Thus you   
>> can turn off/on and set the boundary. Left in the other prims as   
>> agreed.
>
> Thanks, this sounds good.
>
>> a) The 10 entries I have for FinalizationDependents have sizes of #(0  
>> 2  0 3 2 55825 nil nil nil nil). You will note the one with 55,825   
>> entries. This actually a 98K or so WeakIdenityKeyDictionary of   
>> CompiledMethods.
>
> This is not the case in any image I am using. You must be using a  
> non-standard image; all the regular ones that I've checked have  #(0 2  
> nil nil nil nil nil nil nil nil) (0: Sockets; 2: Files).


Well no it's not a non-standard image, rather it's a working image  
floating about that I have VMMaker in, but the problem is I filed in  
your code from your note of Nov 11th/ 2004 (below) when you were  
talking about issues with the finalization process and CPU performance.  
Seems I filed this in and save the image (duh! well that was dumb). For  
some reason the macrobenchmark triggers a weak object GC event base on  
the new changes which then grinds thru the 48K  
WeakIdentityKeyDictionary and as you point out that's CPU intensive.

Smalltalk removeKey: #CPUHog of course fixes things.


> I've seen this problem myself. It is easiest to see what happens when  
> you have a process browser open and turn on the cpu watcher - this  
> will show that the finalization process takes a huge amount of  
> resources.
>
> But why? Most likely (this was the case I have experienced) you have  
> created some weak collection with what I consider "automatic  
> finalization", e.g., WeakRegistry and friends register themselves to  
> get notified when a weak references got freed. If this registry grows  
> very large it can take significant amounts of time to do the  
> finalization and if your code is then weak reference heavy you may  
> spend a lot of time in finalization.
>
> Here is an example illustration the problem:
> | hog proc |
> hog := WeakIdentityKeyDictionary new.
> CompiledMethod allInstancesDo:[:cm| hog at: cm put: 42.0].
> Smalltalk at: #CPUHog put: hog.
> WeakArray addWeakDependent: hog.



> --
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John M. McIntosh <jo...@sm...> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
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