RFR (XS): 8021879: G1: G1HeapRegionSize flag value not updated correctly

Bengt Rutisson bengt.rutisson at oracle.com
Tue Jul 30 12:11:38 UTC 2013


Hi everyone,

Could I have a couple of reviews for this very small change?

http://cr.openjdk.java.net/~brutisso/8021879/webrev.00/

Background:

The G1HeapRegionSize flag is not updated with the actual value of the 
region size. This makes it impossible to figure out the heap region size 
using PrintFlagsFinal:

$ java -XX:+UseG1GC -XX:+PrintFlagsFinal -version | grep G1HeapRegionSize
     uintx G1HeapRegionSize = 0 {product}

Or when setting it to the wrong value (this will actually use a region 
size of 8m):

$ java -XX:+UseG1GC -XX:G1HeapRegionSize=11m -XX:+PrintFlagsFinal 
-version | grep G1HeapRegionSize
     uintx G1HeapRegionSize := 11534336 {product}


With the proposed patch I get this output:

$ java -XX:+UseG1GC -XX:+PrintFlagsFinal -version | grep G1HeapRegionSize
     uintx G1HeapRegionSize                         := 1048576         
{product}

and:

$ java -XX:+UseG1GC -XX:G1HeapRegionSize=11m -XX:+PrintFlagsFinal 
-version | grep G1HeapRegionSize
     uintx G1HeapRegionSize                         := 8388608         
{product}


Here are also some interesting scenarios that are visible with my 
suggested patch:

$ java -XX:+UseG1GC -Xmx64g  -XX:+PrintFlagsFinal -version | grep 
G1HeapRegionSize
     uintx G1HeapRegionSize                         := 1048576         
{product}

$ java -XX:+UseG1GC -Xms64g -Xmx64g  -XX:+PrintFlagsFinal -version | 
grep G1HeapRegionSize
     uintx G1HeapRegionSize                         := 33554432        
{product}

Thanks,
Bengt
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