[Caml-list] Immediate Out_of_memory

[Caml-list] Immediate Out_of_memory

[Tom Hawkins]

After making a few minor changes, my program started raising the 
Out_of_memory exception.  The strange thing is it fires a split 
second after the program starts.  It happens so fast, 'top' doesn't 
even have a chance to register it on its radar.

I narrowed it down to a 'Hashtbl.find' application.  Just prior to the 
statement I did a 'Gc.print_stat stdout':

minor_words: 1044856
promoted_words: 360738
major_words: 371008
minor_collections: 31
major_collections: 6
heap_words: 368640
heap_chunks: 6
top_heap_words: 368640
live_words: 352563
live_blocks: 83968
free_words: 15973
free_blocks: 513
largest_free: 9539
fragments: 104
compactions: 0
Fatal error: exception Out_of_memory

Do these numbers look OK?  I have 249MB of total swap memory, with 
currently 216 MB free.  Any ideas?

The results are the same for both 3.07+2 and 3.08.0.

I'll try to produce a simplified test case.  Unfortunately it's in a 
rather convoluted spot in the application.

Thanks for any help.

-Tom


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Re: [Caml-list] Immediate Out_of_memory

[Xavier Leroy]

> After making a few minor changes, my program started raising the 
> Out_of_memory exception.  The strange thing is it fires a split 
> second after the program starts.  It happens so fast, 'top' doesn't 
> even have a chance to register it on its radar.
> I narrowed it down to a 'Hashtbl.find' application.

This is very likely due to a structural comparison (via =, like
Hashtbl.find does) between cyclic structures.  Structural comparison
maintains a recursion stack that is bounded, and raises Out_of_memory
when that stack overflows.  With 3.08, you can confirm this hypothesis
by running with OCAMLRUNPARAM set to 'v=63'; structural comparison
will print a message if it runs out of recursion stack.

- Xavier Leroy

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Re: [Caml-list] Immediate Out_of_memory

[Tom Hawkins]

On Tuesday 13 July 2004 09:32 am, Xavier Leroy wrote:
> > After making a few minor changes, my program started raising the
> > Out_of_memory exception.  The strange thing is it fires a split
> > second after the program starts.  It happens so fast, 'top'
> > doesn't even have a chance to register it on its radar.
> > I narrowed it down to a 'Hashtbl.find' application.
>
> This is very likely due to a structural comparison (via =, like
> Hashtbl.find does) between cyclic structures.  Structural
> comparison maintains a recursion stack that is bounded, and raises
> Out_of_memory when that stack overflows.  With 3.08, you can
> confirm this hypothesis by running with OCAMLRUNPARAM set to
> 'v=63'; structural comparison will print a message if it runs out
> of recursion stack.

Yes, that's it.

Many thanks for 3.08.

-Tom


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