[plt-scheme] MzScheme maximum memory use

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Thu Jul 12 04:43:36 EDT 2007

At Thu, 12 Jul 2007 09:38:28 +0100, "Noel Welsh" wrote:
> Am I correct in thinking the maximum amount of memory that MzScheme
> can use on a 32-bit platform is 2GB?  I assume 32-bits - 1 tag bit =
> 31 bits for every pointer.  This would explain why we ran out of
> memory on a machine with 3GB RAM and the web server's LRU manager set
> w/ a max consumption of 2GB.

The tag bit is 0 in the low-order position, which means that all
objects have to be aligned on short words. All objects aligned on
longwords, anyway. So that's not the obstacle.

The problem is more likely the 3m GC, which thinks that it may need
twice the heap space to perform a collection, so it's unwilling to
allocate past 2GB (given a 4GB address space). This shouldn't be
difficult to improve, but I haven't gotten around to it.


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