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Re: Garbage collection in OCaml
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Date: 2000-10-02 (19:30)
From: David McClain <dmcclain@a...>
Subject: Re: Garbage collection in OCaml
Yes, Thanks so much for your helpful suggestions! Your Gc settings were what
I was hoping to find from someone with insight to the behavior of the GC. I
am trying them as we speak!


- DM

-----Original Message-----
From: Damien Doligez <>
To: <>
Date: Monday, October 02, 2000 4:32 AM
Subject: Re: Garbage collection in OCaml

>>From: "David McClain" <>
>>I have a long running analysis program written in compiled OCaml
>>If I let it run without interference it gradually allocates more and more
>>memory until the system swap space is exhausted. At that point the program
>>bombs off with an "out of memory" errror - probably generated by the OCaml
>>array management routines.
>Most likely, a fragmentation problem.  If you're using a lot of arrays
>or strings with different sizes, it can happen.
>>OTOH, I found by tinkering that placing a Gc.compact() in a periodically
>>performed place, I manage to keep the entire system running within about
>>MBytes. (My machines all have 256 MB RAM or more).
>Thus we know for sure it was a fragmentation problem.
>>I have found that placing a Gc.full_major() does virtually nothing to
>>prevent the exhaustion of memory, although it slows it down ever so
>Gc.full_major() is not going to help, that's normal.
>>The program was compiled to run with the default GC settings (whatever
>>are). That is to say, I did nothing to configure the GC system at program
>>Is this behavior normal? Must I plant strategic Gc.compact() in my code? I
>>would have thought the GC would be more self monitoring.
>Calling Gc.compact() is one solution.  You could also try setting
>max_overhead in the Gc.control record.  For example, if you do:
>  Gc.set { (Gc.get ()) with Gc.max_overhead = 200 }
>then Gc.compact() will get called automatically when the free memory
>is 200% the size of the live data.  This setting is not activated by
>default because compaction is not incremental, so it introduces a long
>pause in the computation, which would be annoying for an interactive
>-- Damien