Re: [rvm-research] Jikes Code Cache Management

On 5/7/2013 1:39 PM, Pushparaj Motamari wrote:

> I need help regarding Good resources to start understanding the Code Cache Management in JikesRVM?

Dear Pushparaj -- AFAIK it is not something I would actually
call a cache.  Code gets generated for some methods as part of
the system build process (namely for those methods needed by
the system itself).  When the system is about to run a method
that has not yet been compiled, then the method will be compiled.
The default policy will use the "baseline" (non-optimizing)
compiler.  There are various controls that can override the
policy.

If a method is seen to be executed frequently enough, it will
be re-compiled with the optimizing compiler -- sometimes multiple
times (at increasing levels of optimization).  Future calls
go to the latest version, and it is even possible to redirect
calls *currently in progress* to new code using a technique
called On Stack Replacement (OSR).  If you want to grasp that,
I recommend reading the conference paper about it.

Anyway, as newer version are compiled, older ones fall into
disuse, but AFAIK the space is not reclaimed.  Compiled code
resides in a space separate from the main garbage collected
heap, and is never moved by the GC, which means that references
to code, or positions within code (e.g., return addresses)
do not have to be updated.  (If I am wrong about the space
being reclaimed, then clearly it is managed by a mark-sweep /
free-list kind of technique.)

So, is the space management you wanted to know about, really,
or the recompilation policies?

Regards -- Eliot Moss

------------------------------------------------------------------------------
Learn Graph Databases - Download FREE O'Reilly Book
"Graph Databases" is the definitive new guide to graph databases and 
their applications. This 200-page book is written by three acclaimed 
leaders in the field. The early access version is available now. 
Download your free book today! http://p.sf.net/sfu/neotech_d2d_may