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Hi Bengt,<br>
Above all, please confirm with your final say about the change.<br>
<br>
Thanks.<br>
Tao<br>
<br>
On 2/12/2013 12:03 PM, Tao Mao wrote:
<blockquote cite="mid:511AA025.7050603@oracle.com" type="cite">
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
Hi all,<br>
<br>
After some investigation of the code, I figured out that the only
opportunity where my change will affect something is in
MarkSweepPolicy, which is supposed to support sizing policy (if
any) for UseSerialGC [1].<br>
<br>
But, I think, SerialGC hasn't implemented any sizing policy
associated with flags MaxGC*PauseMillis (I'm not sure about it
tho/<span class="moz-smiley-s3"></span>). So, we can conclude that
if a customer uses SerialGC, they wouldn't set MaxGC*PauseMillis
anyway. <br>
<br>
(Bengt and Jon, please help verify the above conclusion.)<br>
<br>
Therefore, the change will fix the initialization bug in a safe
way. <br>
<br>
It did take me a while to figure out the class and method
hierarchy. I share the diagram as a pic below. Hopefully, we can
use it to build up a better class design if possible.<br>
<br>
Sorry for the handwriting and not being able to draw a fancier
diagram in text <span class="moz-smiley-s1"></span>.<br>
<br>
Thanks.<br>
Tao<br>
<br>
[1] in Universe::initialize_heap()<br>
<br>
if (<font color="#ff0000">UseParallelGC</font>) {<br>
#ifndef SERIALGC<br>
Universe::_collectedHeap = new ParallelScavengeHeap();<br>
#else // SERIALGC<br>
fatal("UseParallelGC not supported in this VM.");<br>
#endif // SERIALGC<br>
<br>
} else if (<font color="#ff0000">UseG1GC</font>) {<br>
#ifndef SERIALGC<br>
G1CollectorPolicy* g1p = new G1CollectorPolicy();<br>
G1CollectedHeap* g1h = new G1CollectedHeap(g1p);<br>
Universe::_collectedHeap = g1h;<br>
#else // SERIALGC<br>
fatal("UseG1GC not supported in java kernel vm.");<br>
#endif // SERIALGC<br>
<br>
} else {<br>
GenCollectorPolicy *gc_policy;<br>
<br>
if (<font color="#ff0000">UseSerialGC</font>) {<br>
gc_policy = new MarkSweepPolicy();<br>
} else if (<font color="#ff0000">UseConcMarkSweepGC</font>) {<br>
#ifndef SERIALGC<br>
if (<font color="#ff0000">UseAdaptiveSizePolicy</font>) {<br>
gc_policy = new ASConcurrentMarkSweepPolicy();<br>
} else {<br>
gc_policy = new ConcurrentMarkSweepPolicy();<br>
}<br>
#else // SERIALGC<br>
fatal("UseConcMarkSweepGC not supported in this VM.");<br>
#endif // SERIALGC<br>
} else { // default old generation<br>
gc_policy = new MarkSweepPolicy();<br>
}<br>
<br>
Universe::_collectedHeap = new GenCollectedHeap(gc_policy);<br>
}<br>
<br>
<br>
<img src="cid:part1.08050005.01020405@oracle.com" alt=""><br>
<br>
On 2/10/2013 1:34 PM, Bengt Rutisson wrote:
<blockquote cite="mid:51181278.8090401@oracle.com" type="cite">
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http-equiv="Content-Type">
<div class="moz-cite-prefix"><br>
<br>
Hi Tao,<br>
<br>
Thanks for your answers. Some comments inline.<br>
<br>
On 2/9/13 12:44 AM, Tao Mao wrote:<br>
</div>
<blockquote cite="mid:51158DCC.2020205@oracle.com" type="cite">
<meta content="text/html; charset=UTF-8"
http-equiv="Content-Type">
<div class="moz-cite-prefix">I'm trying to answer these
questions. Please see inline. Thanks.<br>
Tao<br>
<br>
On 2/8/13 8:17 AM, Bengt Rutisson wrote:<br>
</div>
<blockquote cite="mid:51152519.9030109@oracle.com" type="cite">
<br>
Hi Tao, <br>
<br>
I think the change looks good and makes sense. <br>
<br>
But I have a hard time estimating the implications of this
change. <br>
<br>
It seems like MaxGCMinorPauseMillis is only used by CMS and
ParallelScavenge. </blockquote>
You are right. Before the fix, four occurrences below. (The
one in collectorPolicy.cpp is suspected to be wrong)<br>
<br>
MaxGCMinorPauseMillis is introduced in different kinds of
classes for CMS and PS: ConcurrentMarkSweep<b>Policy</b> and
ParalleScavenge<b>Heap</b>.<br>
<br>
$ grep -nr "MaxGCMinorPauseMillis"
src/src/share/vm/gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.cpp:87:
double max_gc_minor_pause_sec = ((double)
MaxGCMinorPauseMillis)/1000.0;<br>
src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp:156:
double max_gc_minor_pause_sec = ((double)
MaxGCMinorPauseMillis)/1000.0;<br>
src/share/vm/memory/collectorPolicy.cpp:170: const double
max_gc_minor_pause_sec = ((double)
MaxGCMinorPauseMillis)/1000.0;<br>
src/share/vm/runtime/globals.hpp:2043: product(uintx,
MaxGCMinorPauseMillis, max_uintx, \<br>
<blockquote cite="mid:51152519.9030109@oracle.com" type="cite">For
both of those the default for MaxGCMinorPauseMillis is the
same as MaxGCPauseMillis so it should be fine. <br>
</blockquote>
How did you infer that the default value for
MaxGCMinorPauseMillis is same as MaxGCPauseMillis? I didn't
see such an indication in the code.<br>
</blockquote>
<br>
I actually ran with both collectors using -XX:+PrintFlagsFinal
and looked at the values printed. But you find it in the code
too. Both flags are declared in globals.hpp as having max_uintx
as default value:<br>
<br>
<br>
product(uintx, MaxGCPauseMillis,
max_uintx, \<br>
"Adaptive size policy maximum GC pause time goal in
msec, " \<br>
"or (G1 Only) the max. GC time per MMU time
slice") \<br>
<br>
product(uintx, MaxGCMinorPauseMillis,
max_uintx, \<br>
"Adaptive size policy maximum GC minor pause time goal
in msec") \<br>
<br>
<br>
<br>
<blockquote cite="mid:51158DCC.2020205@oracle.com" type="cite">
<blockquote cite="mid:51152519.9030109@oracle.com" type="cite">
<br>
But what happens if a customer is running with
-XX:MaxGCMinorPauseMillis=1000 but not setting
MaxGCPauseMillis on the command line? What are the
implications of your change for such runs? I don't think it
is very common. Just thinking. <br>
</blockquote>
For ParallelScavenge, customers should distinguish the two
flags.<br>
</blockquote>
<br>
Yes, they should, but my point was that if a customer was just
setting one of the flags their application might behave
differently now. And I was trying to understand in what way it
would behave different. But I actually think that your change
will not affect ParallelScavenge anyway. See below.<br>
<br>
<blockquote cite="mid:51158DCC.2020205@oracle.com" type="cite">
For CMS, I wonder whether we have fully implemented adaptive
sizing policy. Jon, can you comment on this?<br>
In either case, customers should be able to tell apart.<br>
</blockquote>
<br>
You are correct. Implementing adaptive sizing was never
completed for CMS so, it is turned off. Let's ignore CMS for
now.<br>
<br>
<blockquote cite="mid:51158DCC.2020205@oracle.com" type="cite">
<blockquote cite="mid:51152519.9030109@oracle.com" type="cite">
<br>
Also, a more common case is probably to run with only
-XX:MaxGCPauseMillis set on the command line. How will the
adaptive sizing behave differently compared to before? <br>
</blockquote>
The fix only changed the value in the routine
GenCollectorPolicy::initialize_size_policy, which is believed
to be called within<br>
the routine of GenCollectedHeap::post_initialize(). I'm not
sure whether this routine can change sizing behaviors
somewhere.<br>
</blockquote>
<br>
post_initialize() is called from universe_post_init() for all
collectors. But only the CollectedHeaps that inherit from
GenCollectedHeap will be affected by your change.<br>
<br>
ParallelScavengeHeap does not inherit from GenCollectedHeap and
it implements its own post_initialize(), so I think it is
unaffected by your change.<br>
<br>
So, that's why I came to the conclusion that the code that your
are changing is actually not being used by anyone. If this is
correct I think your change is safe and for the better. But I
also think that we could possibly clean up the code and get rid
of some code paths. This should probably be done as a separate
change though.<br>
<br>
Bengt<br>
<br>
<br>
<br>
<blockquote cite="mid:51158DCC.2020205@oracle.com" type="cite">
<blockquote cite="mid:51152519.9030109@oracle.com" type="cite">
<br>
Looking closer at the code it looks like CMS and
ParallelScavenge are actually using CMSAdaptiveSizePolicy
and PSAdaptiveSizePolicy respectively. Both of these already
pass the correct value to the constructor of the super class
AdaptiveSizePolicy. So, this bug is currently benign. The
code that you are changing is actually not being used. Is
this a correct conclusion? <br>
</blockquote>
See above. Whether the code I'm changing is being used depends
upon whether GenCollectedHeap::post_initialize() is called
anywhere. But I can't determine that right now.<br>
<br>
Other than that, the fix should correct the bug while
preserving everything else.<br>
<blockquote cite="mid:51152519.9030109@oracle.com" type="cite">
<br>
Thanks, <br>
Bengt <br>
<br>
On 2/8/13 3:42 AM, Tao Mao wrote: <br>
<blockquote type="cite">8007764: Wrong initialized value of
max_gc_pause_sec for an instance of class
AdaptiveSizePolicy <br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="https://jbs.oracle.com/bugs/browse/JDK-8007764">https://jbs.oracle.com/bugs/browse/JDK-8007764</a>
<br>
<br>
webrev: <br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Etamao/8007764/webrev.00/">http://cr.openjdk.java.net/~tamao/8007764/webrev.00/</a>
<br>
<br>
changeset: <br>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
</blockquote>
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