Re: [rvm-research] about specifying GC space size and heap size

Hi,

On 26/10/2008, at 7:39 AM, weiming zhao wrote:
Yes, you can specify the amount of virtual memory for a space.  We try  
to avoid this as much as possible so as not to tie down virtual  
memory.  By default, most spaces will be constructed to use  
discontiguous space (ie they share virtual memory).  However, you can  
specify some virtual memory range if you wish using a VMRequest.  This  
is done by passing an argument to VMRequest.create().   If no argument  
is passed, a default discontiguous request handle is created.   In  
most cases this is what we do.

For an example of where we do pin down virtual memory, at the  
constructor for the default space in the NoGC plan.  You will see it  
is constructed to use 0.6 of all available virtual memory:
        VMRequest.create(0.6f);

Note that the above comments will be correct for the 3.0.X releases,  
but not necessarily for older releases.

This is a completely different matter.

Here you are talking about how many pages are *consumed* by a space at  
any point in time.  This is entirely different (strictly less than or  
equal) to the amount of virtual memory reserved for a given space.    
Virtual memory is reserved ahead of time (it is a static property of a  
plan), while the page count is a dynamic property depending on how the  
heap is utilized at any point in time.

You need to override getPagesUsed() for your particular plan.  This  
should add the usage of any space defined in the plan to that in the  
super class.  Here is the definition for SemiSpace:

   public int getPagesUsed() {
     return super.getPagesUsed() + toSpace().reservedPages();
   }

You also *may* need to override getPagesAvail() for your particular  
plan.  In the case of SemiSpace, we must account for a copy reserve  
(ie a 2 X space overhead), so getPagesAvail() for SemiSpace is defined  
thus:

   public final int getPagesAvail() {
     return(super.getPagesAvail()) >> 1;
   }

If you don't have a copy reserve or any other such special requirement  
for your plan, then you don't need to override getPagesAvail().

--Steve


-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________
Jikesrvm-researchers mailing list
Jikesrvm-researchers@...
https://lists.sourceforge.net/lists/listinfo/jikesrvm-researchers