From: Yukihiro Matsumoto <matz@...>
Date: 2008-02-22T05:51:28+09:00
Subject: Re: GC error ?

Hi,

In message "Re: GC error ?"
    on Fri, 22 Feb 2008 05:17:03 +0900, "Rick DeNatale" <rick.denatale@gmail.com> writes:

|Yes, and it also suffers from two facts that make it perform
|sub-optimally on a virtual memory system (i.e. just about any system
|these days)
|
|1) It fails to compact the live objects
|2) It pretty much is guaranteed to visit every memory page at least
|twice per GC cycle.

Indeed, we need two visits (one write to mark live objects/one read to
sweep dead objects) per GC.  But using bitmap marking technique[1],
objects visit can be reduced to one.

[1] http://izumi.plan99.net/blog/index.php/2008/01/14/making-ruby%e2%80%99s-garbage-collector-copy-on-write-friendly-part-7/

There's an algorithm named "mostly copying GC" to address the former
"fact", but it is too complex for us to implement.

							matz.