Re: New bug-classpath mailinglist

[Robert Lougher]

Hi,

> Sorry, I didn't mean it as a dig at JamVM and believed I had already
> mentioned this on list earlier.

Please have a dig at JamVM if there's a problem!  I wanted to know
what the problems were because it's Sunday, and I would have had a
chance to look at it, if it was a serious issue.  Unfortunately, from
the sounds of it, it's a long running problem...

> The problems I had (early this year --
> as I say, I haven't had chance to try again yet) were related to firstly
> missing methods in Classpath (java.nio constructors for the input and
> output streams being used, something I believe is now fixed) and then
> memory problems with JamVM.   It isn't so much a problem with JamVM, as
> the amount of memory used.  findbugs uses a lot of memory, and JamVM, I
> guess, doesn't garbage-collect it efficiently enough to avoid running
> out (a problem I've also seen with one of my own applications).  I
> repeatedly scaled up the memory given to JamVM, but failed to get a
> successful run of it with Classpath without running out.  At 512mb, it
> caused a kernel OOM.  It does work with smaller projects; it's a problem
> with large projects like Classpath, which has a huge number of classes
> (and even more now).

This is really interesting.  Because JamVM doesn't use handles, heap
compaction is tricky, and I haven't implemented it yet :)  My guess
would be that the allocation pattern is leading to particularly heavy
heap fragmentation, forcing heap expansion even when sufficient memory
is available.  I've read up on the algorithms and worked out a
modified Jonkers, but in the end I wasn't sure whether fragmentation
was a big enough issue in real-life, with 256Mb+ memories.  This
proves it is.

Thanks,

Rob.

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