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Date:Mon Oct 14 12:12:33 1993 
Subject:Re: GC (instead of Threaded Interpreted Languages!) 
From:Helen McCall - PML Mast2 
Volume-ID:931015.09 


Thank you all for the illuminating comments on my problems with POPLOG memory management.

Aaron, Steve, et al have made numerous suggestions ranging from broken hardware or broken OS, through bad POPLOG executable image, down to use/misuse of POP-11 language features.

As far as I am aware (following reboots & fs checks &c) the hardware and OS are not faulty.

The fact that POPLOG, once it has become deranged, remains deranged until reloaded, suggests strongly that the image is being hit in some way.

Aaron has suggested that I might be using/misusing fast_ procedures.  He is correct! 

I had not realised that this means that it does not do the normal memory checks. 

I had been tempted to use these fast_ procedures because I am performing computationally expensive calculations on very large data sets. This includes performing Fourier transforms on several thousand high definition images in one run. 

During such calculations, which involve comparatively simple programs where one would ideally like each image transformation sequence to utilise the same memory allocation as the previous one, I found that the swap space was gradually eaten up as the garbage collector got to work between each iteration. The proceses which died, did so in an orderly fashion because they had run out of swap space, which suggests that the OS was indeed performing correctly.

I reduced these problems by eliminating the use of large data objects in memory, such as indexed data files loaded as lists, and simply wound through the files record by record instead; which proves much faster than using large linked list structures!

I also found it necessary to quit POPLOG after a big run, to free up the swap space.

I will try eliminating all of the fast_ procedures, and look into the use of gc_copy etc, because these seem the most likely causes of my problems.

Helen.