Re: [Caml-list] Slow GC problem

[Brian Hurt <brian.hurt@qlogic.com>]

In playing around with the C interface code myself, I noticed that 
alloc_custom (the function that IMHO bigarray should be using to allocate 
it's blocks) has two arguments you pass in, which control how often the 
blocks get garbage collected- used and max.  The gcc does a full gc every 
used/max blocks allocated (more or less).

Perhaps the bigarray library should be extended to allow the user to set 
these variables.  I'm wondering if different values here might not solve 
Shivkumar's problem in a more elegant (read: nice) way?

Brian

On Thu, 10 Apr 2003, Shivkumar Chandrasekaran wrote:

> 
> I took Damien's advice (thanks) and spent some time trying to re-use 
> all the bigarrays I was allocating. However, my bigarray use is spread 
> out over a fairly complicated algorithm, and the only way to make a 
> good dent on  bigarray use would be to completely rewrite the algorithm 
> in a more traditional fortran77 style. Which would of course mean that 
> I would have to first figure out the entire memory usage pattern.
> 
> ...... So I am pondering another solution:
> 
> What if I modified bigarray_stubs.c to use the malloc and free calls of 
> the Boehm gc (6.1-4) garbage collector? My reasoning is that malloc is 
> performing poorly due to fragmentation, and switching to a gc'd version 
> might help out.
> 
> Before I try this I would like some feedback from the list on the 
> soundness of this idea. Thanks,
> 
> --shiv--
> 
> On Tuesday, April 8, 2003, at 03:23 AM, Damien Doligez wrote:
> 
> >> I have a gc efficiency problem for which I require some advice. I 
> >> have read both the O'Reilly book and the manual on gc.
> > [...]
> >>  Below I give the gc stats just before and after the solver routine 
> >> is called in the in-core solver:
> >>
> >> 				"Just before"	"Just after"
> >> minor_words:		46243376	139259767
> >> promoted_words:	928267		2595523
> >> major_words:		2883087		39489766
> >> minor_collections:	1412		4591
> >> major_collections:	18			52
> >> heap_words:		2150400		1044480
> >> heap_chunks:		35			17
> >> top_heap_words:	2150400		5038080
> >> live_words:		1842373		840037
> >> live_blocks:		253926		116816
> >> free_words:		307180		204440
> >> free_blocks:		47368		17
> >> largest_free:		10928		61440
> >> fragments:		847			3
> >> compactions:		0			2
> >
> > As others have said, this is not really enough information to tell
> > what is going on.  What we can say from the above is:
> >
> > 1. You are allocating lots and lots of data structures in the major
> >    heap (maybe finalized bigarray descriptors)
> > 2. The compactor was called twice, which may indicate that you have
> >    a fragmentation problem.
> > 3. The compactor was called near the end of the solver routine,
> >    which must have erased most of the evidence...
> >
> > -- Damien
> >
> --shiv--
> 
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