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Bengt,<br>
<br>
First, very good catch! And I agree with you that a) SurvRateGroup
does need some tidying up and b) you're taking the right approach in
keeping this fix simple at this time.<br>
<br>
The fix looks great, some minor comments below:<br>
<br>
<pre><span class="changed"> 41 _surv_rate_pred(NULL),</span>
<span class="changed"> 42 _stats_arrays_length(0)</span>
43 {
44 reset();
45 if (summary_surv_rates_len > 0) {
46 size_t length = summary_surv_rates_len;
47 _summary_surv_rates = NEW_C_HEAP_ARRAY(NumberSeq*, length);
48 if (_summary_surv_rates == NULL) {
49 vm_exit_out_of_memory(sizeof(NumberSeq*) * length,
50 "Not enough space for surv rate summary");
51 }
52 for (size_t i = 0; i < length; ++i)
53 _summary_surv_rates[i] = new NumberSeq();
54 }
</pre>
Since you removed the NULL check in the other places where
NEW_C_HEAP_ARRAY() is called, any chance of doing that here too to
be consistent throughout the file? Also, (and this is really picky!)
could you move the curly bracket on line 43 to the line above (you
did in the reset() method) and put curly brackets around the body of
the for-loop? Thanks!<br>
<br>
<pre><span class="removed"> 92 #if 0</span>
<span class="removed"> 93 gclog_or_tty->print_cr("[%s] stop adding regions, length %d", _name, _region_num);</span>
<span class="removed"> 94 #endif // 0</span>
<span class="removed"></span></pre>
Since you removed this, any chance of maybe removing the other
instances of #if 0 gclog_or_tty->print_cr(...); #endif // 0?<br>
<br>
On 03/13/2012 04:49 AM, Bengt Rutisson wrote:
<blockquote cite="mid:4F5F0A10.7050301@oracle.com" type="cite">
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
<br>
Hi John,<br>
<br>
Thanks for the review!<br>
<br>
Here is an updated webrev:<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Ebrutisso/7152954/webrev.01/">http://cr.openjdk.java.net/~brutisso/7152954/webrev.01/</a><br>
<br>
Some comments inline...<br>
<br>
On 2012-03-13 00:03, John Cuthbertson wrote:
<blockquote cite="mid:4F5E80DD.6030801@oracle.com" type="cite">
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
Hi Bengt,<br>
<br>
Looks good - but I do have a couple of comments:<br>
<br>
survRateGroup.cpp:<br>
<br>
This is not related to your changes - but I just noticed it:<br>
<br>
<pre> 108 _surv_rate_pred = NEW_C_HEAP_ARRAY(TruncatedSeq*, _region_num);
109 if (_surv_rate == NULL) {
110 vm_exit_out_of_memory(sizeof(TruncatedSeq*) * _region_num,
111 "Not enough space for surv rate pred array.");
112 }
</pre>
should be:<br>
<br>
<pre> 108 _surv_rate_pred = NEW_C_HEAP_ARRAY(TruncatedSeq*, _region_num);
109 if (<b>_surv_rate_pred</b> == NULL) {
110 vm_exit_out_of_memory(sizeof(TruncatedSeq*) * _region_num,
111 "Not enough space for surv rate pred array.");
112 }
</pre>
</blockquote>
<br>
You are correct, but NEW_C_HEAP_ARRAY will call
vm_exit_out_of_memory() if the allocation fails. So this is dead
code. I removed it instead of updating it.<br>
<br>
<blockquote cite="mid:4F5E80DD.6030801@oracle.com" type="cite"> My
picture of SurvRateGroup::stop_adding_regions() has always been
that it's just extending the stats arrays (i.e., a realloc
operation). So, with that picture in mind, the following lines:<br>
<br>
<pre><span class="changed"> 117 for (size_t i = _stats_arrays_length; i < _prev_stats_arrays_length; ++i) {</span>
<span class="changed"> 118 delete old_surv_rate_pred[i];</span>
<span class="changed"> 119 }</span>
</pre>
really look like they belong in SurvRateGroup::reset().<br>
</blockquote>
<br>
Good point. I was struggling a bit with how this code was supposed
to be used. I moved the delete calls into reset(). Thanks for
pointing this out. <br>
<br>
<blockquote cite="mid:4F5E80DD.6030801@oracle.com" type="cite">
Excellent catch - what brought it to your attention?<br>
</blockquote>
<br>
It is kind of a funny story. Here is probably more information
than you want, so just stop reading if you find it too long ;-)<br>
<br>
I just wanted to confirm that a small test I found would
eventually throw an OOME. I ran it on JDK7 b147 over a weekend.
When I checked the test after the weekend it had gotten a native
out of memory instead. The test would mostly allocate humongous
objects so I figured we were leaking in this respect somehow.<br>
<br>
I instrumented a build from the tip of hotspot-gc. But to my
surprise the leak was gone. That's when I realized that in b147 we
were constantly doing full GCs to handle all the humongous
objects. But in the latest builds we have the fix I made to
initiate concurrent marking on humongous object allocations, so we
never did any full GCs. By inducing full GCs with System.gc()
calls I could show that the memory leak was in fact still present
in the latest builds as well.<br>
<br>
I tried out the prototype that Zhengyu has for native memory
tracking. Unfortunately I didn't get it to work properly on my 64
bit system. After I had already found the cause of the leak,
Zhengyu ran my reproducer on a 32 bit system and got this report:<br>
<br>
[0x54dd14fc] TruncatedSeq::TruncatedSeq+0x4c<br>
(malloc=162KB 143KB, #2071 1833)<br>
<br>
[0x54f43737] SurvRateGroup::reset+0x47<br>
(malloc=128KB 115KB, #2049 1833) <br>
<br>
That is really spot on (assuming
SurvRateGroup::stop_adding_regions() got inlined into
SurvRateGroup::reset()). So, it looks to me as though NMT will be
a really useful tool to find this type of issues in the future.<br>
<br>
Once I had the small reproducer that just calls System.gc() in a
loop I could manually do a binary search of the full GC code to
find out where we were leaking.<br>
<br>
Long story short: I found this by accident and NMT will be a
really good tool.<br>
<br>
Bengt<br>
<br>
<br>
<br>
<blockquote cite="mid:4F5E80DD.6030801@oracle.com" type="cite"> <br>
JohnC<br>
<br>
<br>
On 03/12/12 02:36, Bengt Rutisson wrote:
<blockquote cite="mid:4F5DC3A1.1050306@oracle.com" type="cite"><br>
Hi all, <br>
<br>
Could I have a couple of reviews for this fairly small change:
<br>
<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Ebrutisso/7152954/webrev.00/">http://cr.openjdk.java.net/~brutisso/7152954/webrev.00/</a>
<br>
<br>
The CR will be publicly available soon here: <br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7152954">http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7152954</a>
<br>
<br>
<br>
I choose to do a fairly small fix. To me it looks like the
SurvRateGroup class could benefit from some refactoring. Maybe
this hole issue could go away with some simplifications to the
code. But I'd like to keep the change as small as possible for
now just in case we would like to push this into hs23. <br>
<br>
<br>
Background from the CR: <br>
<br>
There is a memory leak in the full GC code for G1. This can be
seen by running this simple reproducer: <br>
<br>
public class SysGC { <br>
public static void main(String[] args) { <br>
while (true) { <br>
System.gc(); <br>
} <br>
} <br>
} <br>
<br>
I run it with this command line: <br>
<br>
java -XX:+UseG1GC -Xms16m -Xmx16m -XX:+PrintGC SysGC <br>
<br>
Watching the memory footprint for the java process shows that
it is constantly using more memory. <br>
<br>
The leak comes from SurvRateGroup::stop_adding_regions() which
is called from SurvRateGroup::reset(), which in turn is called
from G1CollectorPolicy::record_full_collection_end(). <br>
<br>
The problem with SurvRateGroup::stop_adding_regions() is that
it does: <br>
<br>
_surv_rate_pred[i] = new TruncatedSeq(10); <br>
<br>
in a loop every time it is called. But there is no
corresponding call to delete. <br>
<br>
Adding a loop to call delete on the previously allocated
TruncatedSeq objects is not enough to solve the problem since
TruncatedSeq is itself allocating an array without freeing it.
Adding a destructor to TruncatedSeq that frees the allocated
array solves the issue. <br>
<br>
With these two fixes the memory leak seems to go away. <br>
<br>
Thanks, <br>
Bengt <br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
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