Re: [Caml-list] A question about GC.

[Gerd Stolpmann <info@gerd-stolpmann.de>]

Am Montag, den 13.06.2011, 09:35 +0900 schrieb Yoonseok Ko:
> Hello everyone.
> I'm a graduate student majoring program analysis.
> 
> I'm using Muddy which is BDD library interfacing Buddy.
> The problem is that when I construct BDD, its memory blows up in some cases
> because GC won't work.
> (It was not only for Muddy problem. We already tried to use our own 
> buddy interface.)
> 
> If I call Gc.compact () explicitly every cycle of constructing BDD, then 
> memory consumption is reasonable.
> Gc.major () also works well, but Gc.minor () doesn't work.
> I watched log messages of GC and figured out that they always try to 
> grow heap and very very rarely start new major GC cycle.
> 
> In a small example, if I construct BDD only in non-tail-recursive form 
> function, memory blows up.
> In a real code, tail-recursive form doesn't work. Just memory blows up.
> So far, only the solution is just call Gc.major () explicitly.
> 
> I'm using GC with default setting.
> There was no memory leakage on buddy side.
> I check the memory consumption both outside of the process and inside of GC.
> 
> 
> I have two questions.
> 
> 1. Is there any solution? Explicit garbage collection is too slow and 
> hard to collect garbage on time.
>      I want to know what happened in GC, and why GC won't work.

Your problem sounds a bit like as if the custom blocks were allocated
with the wrong parameters. Remember caml_alloc_custom has four
parameters:

caml_alloc_custom(ops, size, used, max)

Often one sets here used=0 and max=1, but this may be totally wrong if
you allocate larger blocks. Better set used=1, and max is the number of
custom block allocations until the major GC is triggered. (Imagine there
is a water level variable w, and for every allocation w:=w+used/max, and
if w exceeds 1.0 the water tank is full, and another major GC is
triggered.)

Maybe this helps.

Gerd

> 
> 2. Sometimes GC log has this message: "Growing gray_vals to 32768k bytes."
>      What does that means?
> 
> 
> Best Regards,
> 
> Yoonseok Ko
> 
>