Re: Question about memory size and performance

Yeah, that'd be great -- a GC could then first try to free enough  
memory to satisfy an allocation request within the loaded pages, not  
triggering a page fault, and only GC in non-loaded pages when it can  
not free enough from the loaded pages. Would definitely make sense.  
The beauty of virtual machines is of course that as soon as it gets  
implemented, all code will benefit from it :-)

Attila.

--
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On 2007.12.11., at 2:11, Endre Stølsvik wrote:

> Also, one of the guys that wrote that paper, Matthew Hertz, have also
> written another paper on a subject I liked a lot: GC on VM, as in
> Virtual Memory. I've found that Java sucks when it comes to "managing"
> the memory on a OS with VM, which is pretty much all OSes that matter.
> Since most GCs occasionally will have to do a full collect, ALL pages
> that the JVM have allocated over time will have to be fetched from  
> disk,
> "thrashing" the VM's efforts of sticking unused pages to disk.
>  I believe I might be seeing an effect of this after a virus scan have
> run on my box during the night: most applications are somewhat  
> sluggish
> to restore, except Eclipse, which often are curiously quick to wake  
> up.
>  This is obviously not such a big deal on single-purpose systems, but
> for "Desktop Java" to rule, something should probably be done - a Java
> program cannot go around assuming that it is the only application
> running on a box. (This also goes for the huge memory footprint any
> sized java GUI application is making - multiplying the GC/VM problem).
> This problem should also be present for other GCed languages,  
> like .Net.
>
> However, our guy has an answer: Make the GC interact with the kernel -
> that is, make the kernel have access points to let the processes known
> which pages of theirs are in and out of memory. This seems such an
> obvious idea that I wonder why all OS'es haven't got the feature
> implemented already.

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