On Sat, 08 Oct 2005 01:34:04 +0200, Avi Bryant <avi.bryant at gmail.com>  
wrote:

>
> On Oct 7, 2005, at 4:09 PM, John M McIntosh wrote:
>
>> Of course if you have a  spare GB or two, you could do the fullGC ask  
>> for a block of memory, copy start of memory to end of memory there,  
>> then write that out
>> at your leisure, that forgoes the need for fork and the like. Assumes  
>> of course you can ask and get 500MB at no cost.
>> Surely the write happens quite quickly on modern high-speed disk i/o  
>> machines tho?
>> Seems to me if you're wanting to minimize downtime you fork and do a  
>> snapshot, that as noticed takes upwards of image size to do.
>> Otherwise as you say full GC, fork for the write, but does that  save  
>> anything?
>
> The scenario is that you have a server packed with large images that you  
> want saving to disk periodically.  So mostly what I'm trying to optimize  
> is memory usage, but without unreasonable delay by the standards of web  
> applications.  The two options that take more or less constant memory  
> seem to be a regular snapshot, or GC->fork- >snapshot.  For a largish  
> image (100-200MB), a GC takes maybe 2s (acceptable, if annoying) whereas  
> a snapshot takes maybe 15s (pretty much unacceptable).  So the forking  
> seems like the right choice.  Though if we could get rid of the GC  
> altogether that would be great...

I believe that one of the reasons for GC standing in the way of such an  
application is the lack of integrating it with the virtual memory paging  
mechanism. And 100-200BM is not really that much, IMHO. So it might be  
time for considering an implementation of Squeak based on

http://os.inf.tu-dresden.de/fiasco/

/Klaus

> Avi
>
>
>



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