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From "Xiao-Feng Li (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-4114) [drlvm][gc] GC cannot work with fragmented heap with small heap size
Date Fri, 15 Jun 2007 08:45:26 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-4114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12505104
] 

Xiao-Feng Li commented on HARMONY-4114:
---------------------------------------

I don't think that's a bug. Different VMs or GCs have different max
fragmentation tolerance. It's acceptable. There is no reason to force
DRLVM to behave completely the same as RI.

Actually I found RI also has some problems with this test case. For
example, it throws the exception at MAX 63000000 even without
specifying -Xmx64m, but DRLVM doesn't. But I guess we don't want to
file a bug for DRLVM on this. :-)



-- 
http://xiao-feng.blogspot.com


> [drlvm][gc] GC cannot work with fragmented heap with small heap size
> --------------------------------------------------------------------
>
>                 Key: HARMONY-4114
>                 URL: https://issues.apache.org/jira/browse/HARMONY-4114
>             Project: Harmony
>          Issue Type: Bug
>          Components: DRLVM
>         Environment: Windows
>            Reporter: Vera Petrashkova
>            Assignee: Xiao-Feng Li
>            Priority: Minor
>         Attachments: patch-for-H4114-001.patch
>
>
> VM intermittently throws unexpected OutOfMemoryError on the following test which defines
heap fragmentation.
> This test allocates bytes arrays of different sizes. 
> The arrays sizes are up to the defined MAX memory, but it is always checked that the
total arrays size does not reach this MAX value.
> Some of the arrays are deleted (assigned to null) with the step which varies from 2 to
13, so, fragmentation of heap becomes high. 
> Test fails on DRLVM  with -Xmx64M and sometimes VM crashes on this test without of throwing
OutOfMemoryError.
> On RI this test always passes with -Xmx64Mю
> -------------fragTest.java------------
> public class fragTest {
>     public final static int NUM_IT = 1000000; 
>     public final static int MAX_MEM =  44000000;
>     public final static int BSIZE = 65536;
>     public final static int MIN_BSIZE = 1;
>     public final static int PERIOD = 25000;
>     static int count=0;
>     static int totalSize = 0;
>     public static byte [][] ref = new byte [NUM_IT][];
>     public static void main(String[] args) {
>         int i = 0;
>         try {
>             for (; i < NUM_IT; ++i) {
>                 // size varies from MIN_BSIZE to (BSIZE + MIN_BSIZE)
>                 int size = ((i + BSIZE) % BSIZE) + MIN_BSIZE;
>                 while (totalSize + size > MAX_MEM) {
>                     size = size / 2;
>                     if (size < MIN_BSIZE)
>                         break;
>                 }
>                 if (size >= MIN_BSIZE) {
>                     ref[i] = new byte[size];
>                     totalSize += size;
>                 }
>                 count++;
>                 // clearing of arrays on PERIOD step
>                 if (count > PERIOD) {
>                     // clearing of arrays is perfromed with the step,
>                     // which varies from 2 to 13, so, the heap becomes
>                     // fragmented
>                     int step = (i % 13) + 2;
>                     for(int j = 0; j<i; j+=step) {
>                        if ( ref[j]!= null) {
>                            totalSize-=ref[j].length; //recalculate total size
>                            ref[j]= null;//clear array
>                        }
>                     }
>                     count = 0;
> //                    System.err.println("Total size = " + totalSize);
>                 }
>             }
>             System.err.println("Test passed, Total size = " + totalSize);
>         } catch (OutOfMemoryError e) {
>             System.err.println("OutOfMemoryError is thrown. Total size = "
>                     + totalSize + " i = " + i);
>             System.err.println("Test failed");
>         }
>     }
> }
> -----------------
> Run this test several times.
> java -Xmx64M fragTest
> On RI output always is the following:
> ===============
> java version "1.5.0_06"
> Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
> Java HotSpot(TM) Client VM (build 1.5.0_06-b05, mixed mode)
> Test passed, Total size = 44000000
> DRLVM output:
> =============
> Apache Harmony Launcher : (c) Copyright 1991, 2006 The Apache Software Foundation or
its licensors, as applicable.
> java version "1.5.0"
> pre-alpha : not complete or compatible
> svn = r545076, (Jun  7 2007), Windows/ia32/msvc 1310, release build
> http://harmony.apache.org
> The GC did not provide gc_add_weak_root_set_entry()
> OutOfMemoryError is thrown. Total size = 39269205 i = 50083
> Test failed
> Apache Harmony Launcher : (c) Copyright 1991, 2006 The Apache Software Foundation or
its licensors, as applicable.
> java version "1.5.0"
> pre-alpha : not complete or compatible
> svn = r545076, (Jun  7 2007), Windows/ia32/msvc 1310, release build
> http://harmony.apache.org
> The GC did not provide gc_add_weak_root_set_entry()
> Out of Memory!
> This bug causes the itermittent failures of  gc.frag tests from stress test suite (http://issues.apache.org/jira/browse/HARMONY-3536)

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