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Hi Dima,<br>
<br>
<div class="moz-cite-prefix">On 2015-04-21 13:33, Dmitry Fazunenko
wrote:<br>
</div>
<blockquote cite="mid:55363597.3040006@oracle.com" type="cite">
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<tt>Hi Bengt,<br>
<br>
This is modified fixed based on your comments:<br>
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Edfazunen/8073476/webrev.07/">http://cr.openjdk.java.net/~dfazunen/8073476/webrev.07/</a><br>
<br>
Thanks for your assistance and good ideas!<br>
</tt></blockquote>
<br>
Thanks for making these change. Looks much better to me.<br>
<br>
A couple of comments:<br>
<br>
G1CollectedHeap::do_collection() is only used for full GCs. You
probably want to add a call to G1Log::update_level() in
G1CollectedHeap::do_collection_pause_at_safepoint() too to make sure
that it is called for young GCs as well.<br>
<br>
<br>
I think it looks odd that G1Log::init() and G1Log::update_level()
use different guards for when to take PrintGC and PrintGCDetails
into account.<br>
<br>
51 void G1Log::init() {<br>
52 if (G1LogLevel != NULL && G1LogLevel[0] != '\0')<br>
<br>
37 void G1Log::update_level() {<br>
38 if (FLAG_IS_DEFAULT(G1LogLevel)) {<br>
<br>
Is there a difference between (G1LogLevel != NULL &&
G1LogLevel[0] != '\0') and (FLAG_IS_DEFAULT(G1LogLevel)) ? Can we
use the same guard in both places?<br>
<br>
<br>
g1Log.hpp:<br>
<br>
I don't think this comment helps much:<br>
<br>
+ // to be invoked on VM start <br>
static void init();<br>
<br>
The name init() makes it pretty clear to me what the method is
expected to do. I would just leave the comment out.<br>
<br>
The comment for update_level() talks about where the method should
be called instead of what it does. That is normally not such a good
thing for comments. Better to explain what it does so it can be
called in all places where it is needed in the future.<br>
<br>
So instead of:<br>
<br>
+ // to be invoked on GC start or flag values change<br>
+ static void update_level();<br>
<br>
I would prefer:<br>
<br>
// Update the log level to reflect runtime changes to manageable
flags.<br>
<br>
Thanks,<br>
Bengt<br>
<br>
<blockquote cite="mid:55363597.3040006@oracle.com" type="cite"><tt>
<br>
-- Dima<br>
<br>
<br>
</tt>
<div class="moz-cite-prefix">On 20.04.2015 11:34, Bengt Rutisson
wrote:<br>
</div>
<blockquote cite="mid:5534BA0B.5010906@oracle.com" type="cite">
<meta content="text/html; charset=utf-8"
http-equiv="Content-Type">
<br>
Hi Dima,<br>
<br>
<div class="moz-cite-prefix">On 2015-04-17 15:51, Dmitry
Fazunenko wrote:<br>
</div>
<blockquote cite="mid:55310FCF.5030109@oracle.com" type="cite">
<meta content="text/html; charset=utf-8"
http-equiv="Content-Type">
<tt>Bengt,<br>
<br>
Please find comments inline.<br>
<br>
</tt>
<div class="moz-cite-prefix">On 17.04.2015 9:43, Bengt
Rutisson wrote:<br>
</div>
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">
<meta content="text/html; charset=utf-8"
http-equiv="Content-Type">
<br>
Hi Dima,<br>
<br>
<div class="moz-cite-prefix">On 2015-04-16 15:36, Dmitry
Fazunenko wrote:<br>
</div>
<blockquote cite="mid:552FBAF5.1060908@oracle.com"
type="cite">
<meta content="text/html; charset=utf-8"
http-equiv="Content-Type">
Hi Bengt,<br>
<br>
thanks for looking.<br>
<br>
<div class="moz-cite-prefix">On 16.04.2015 15:42, Bengt
Rutisson wrote:<br>
</div>
<blockquote cite="mid:552FAE22.4020009@oracle.com"
type="cite">
<meta content="text/html; charset=utf-8"
http-equiv="Content-Type">
<br>
Hello Dima,<br>
<br>
<div class="moz-cite-prefix">On 2015-04-16 13:40, Dmitry
Fazunenko wrote:<br>
</div>
<blockquote cite="mid:552F9FA8.3030403@oracle.com"
type="cite">
<meta http-equiv="content-type" content="text/html;
charset=utf-8">
Hello,<br>
<br>
Would you review a simple fix in G1.<br>
<br>
Short description: <br>
after introduction G1Log - dynamic changes of PrintGC
and PrintGCDetails flag has no effect anymore, because
G1Log looks for these flags during initialization
only. The fix: sync the log level with the flags
values.<br>
<br>
A huge thanks to Jesper who helped me a lot with my
first product fix.<br>
<br>
Bug: <a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="https://bugs.openjdk.java.net/browse/JDK-8073476">https://bugs.openjdk.java.net/browse/JDK-8073476</a><br>
Webrev: <a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Edfazunen/8073476/webrev.06/">http://cr.openjdk.java.net/~dfazunen/8073476/webrev.06/</a><br>
</blockquote>
<br>
Sorry, but I don't really like the way this is solved.
With this approach calling G1GCPhaseTimes::print()
suddenly has the side effect that it resets the log
level. That's quite unexpected for me. Especially if you
consider the code path in
G1CollectedHeap::log_gc_footer() where we do this:<br>
<br>
void G1CollectedHeap::log_gc_footer(double
pause_time_sec) {<br>
if (!G1Log::fine()) {<br>
return;<br>
}<br>
<br>
if (G1Log::finer()) {<br>
...<br>
g1_policy()->phase_times()->print(pause_time_sec);<br>
...<br>
}<br>
<br>
If we don't have G1Log::fine() (which is PrintGC)
enabled we will never call the print() method and will
thus not detect any changes made by the MXBean. If we
have G1Log::finer() enabled we enter the logging code,
print other things at the "finer" level (which is
PrintGCDetails) and then do the call to the print()
method where we can suddenly decide that PrintGCDetails
no longer is enabled and not do the rest of the logging.
So for the same GC we will print some stuff at
PrintGCDetails level and some things at another level.
Strange.<br>
</blockquote>
<br>
May it's not clear, but the change will have effect only
if PrintGC or PrintGCDetails has been changed during
execution.<br>
Otherwise, the level will not change.<br>
</blockquote>
<br>
I understand that, but what I was saying with the example
above is that you will not get the desired effect if you
change PrintGC or PrintGCDetails at runtime. If they are
disabled, and then turn them on at runtime you will not
enter the update code because of this check at the start of
the log_gc_footer() method:<br>
<br>
if (!G1Log::fine()) {<br>
return;<br>
}<br>
<br>
<br>
Similarly turning them off at runtime will start to have an
effect in the middle of a GC. Which is probably not the
effect you are looking for.<br>
</blockquote>
fine() invokes level(), level() invokes update(), so
G1::fine() will return the up to date value:<br>
<br>
<pre> inline static bool fine() {
<span class="removed">- return _level >= LevelFine;</span>
<span class="new">+ return level() >= LevelFine;</span>
}</pre>
<br>
<pre> static LogLevel level() {
<span class="new">+ // PringGC and PrintGCDetails are dynamic flags</span>
<span class="new">+ // _level should be in sync with the latest values</span>
<span class="new">+ update_level();</span>
return _level;
}</pre>
<br>
</blockquote>
Oh, I missed that you had changed fine() to call level(). This
means that all calls to G1Log interface has side effects. I
don't like that at all.<br>
<br>
<blockquote cite="mid:55310FCF.5030109@oracle.com" type="cite">
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">
<br>
This is why making the level() getter having the side effect
of changing the log level is a bad idea. You have no control
over when that happens.<br>
</blockquote>
<br>
It must be up to those who change flags at runtime.<br>
But the following code should work:<br>
<br>
MXBean.set(PrintGC, false);<br>
System.gc();<br>
MXBean.set(PrintGC, true);<br>
<br>
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">
<br>
<blockquote cite="mid:552FBAF5.1060908@oracle.com"
type="cite"> <br>
To me, it's strange, that when I disable PrintGC in G1 I
still seeing gc log messages... <br>
Or, I can't turn logging on during execution with G1.<br>
This works well for other collectors.<br>
<br>
Would it make sense to make PrintGC and PrintGCDetails
unmanageable in case of g1?<br>
</blockquote>
<br>
I think they can be manageble but their changed states need
to be handled more explicitly.<br>
<br>
<blockquote cite="mid:552FBAF5.1060908@oracle.com"
type="cite"> <br>
<br>
<blockquote cite="mid:552FAE22.4020009@oracle.com"
type="cite"> <br>
<br>
I would prefer to have a hook when the MXBean changes
the value and only update the level at that point.<br>
</blockquote>
<br>
Yes, it would be ideal solution. But I haven't found such
a mechanism supported. And it's unlikely worth adding just
for this case.<br>
In my version, the sync will be done more frequently. <br>
</blockquote>
<br>
The sync is done very frequently. Actually way too often in
my view.<br>
</blockquote>
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">
<br>
I would prefer that you investigate the hook in the MXBean
change so we know how much work that would be. </blockquote>
<br>
It was my first intention, but I haven't found a way how to
implement it.<br>
</blockquote>
<br>
I think what you need to do is to extend the Flag class with an
update() method and call the method in
WriteableFlags::set_flag().<br>
<br>
<blockquote cite="mid:55310FCF.5030109@oracle.com" type="cite">
<br>
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">If
that is not possible I think a better solution is to call
G1Log::update_level() *once* at the start of a GC. That way
the log level is always consistent throughout the GC.<br>
</blockquote>
<br>
Yes, this is a good idea!<br>
</blockquote>
<br>
Yes, it is much cleaner.<br>
<br>
<blockquote cite="mid:55310FCF.5030109@oracle.com" type="cite">
<br>
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">
<br>
<blockquote cite="mid:552FBAF5.1060908@oracle.com"
type="cite"> <br>
<blockquote cite="mid:552FAE22.4020009@oracle.com"
type="cite"> <br>
Having said that I am not sure that this bug is worth
fixing right now. I am currently working on the JEP to
make the GC logging use the new unified logging format.
That will change all of this and most likely remove the
G1Log class all together. So, my suggestion would be to
leave this as is for now and instead add the MXBean
requirement to the unified logging work.<br>
</blockquote>
<br>
Yes, I'm aware of unified logging and expect that G1Log
class will go away someday.<br>
But I would like to be able to disable logging in JDK9, to
not see GC events occurred at the certain period of time.<br>
</blockquote>
<br>
Can you explain more why this is important to fix right now?
Unified logging is targeted for JDK 9.<br>
</blockquote>
<br>
What I heard about unified logging is that there is no
guarantee that it will happen in JDK9 time frame.<br>
I need the feature now to develop tests based on analysis of
logs: I want to start logging not from begging, but after some
steps.<br>
<br>
Will you be okay if G1Log::update_level() is invoked once per
GC?<br>
</blockquote>
<br>
I would be ok with it, but I'm pretty convinced unified logging
will make it in to JDK9 so if you can wait for it that might be
better.<br>
<br>
Thanks,<br>
Bengt<br>
<br>
<blockquote cite="mid:55310FCF.5030109@oracle.com" type="cite">
<br>
Thanks,<br>
Dima<br>
<br>
<blockquote cite="mid:5530AB92.2050509@oracle.com" type="cite">
<br>
Thanks,<br>
Bengt<br>
<br>
<blockquote cite="mid:552FBAF5.1060908@oracle.com"
type="cite"> <br>
Thanks,<br>
Dima<br>
<br>
<br>
<blockquote cite="mid:552FAE22.4020009@oracle.com"
type="cite"> <br>
Thanks,<br>
Bengt<br>
<blockquote cite="mid:552F9FA8.3030403@oracle.com"
type="cite"> <br>
Testing: <br>
I ran manually the test from the bug report to make
sure the change fixes the problem.<br>
A regression test will be delivered separately as a
fix of <a moz-do-not-send="true" id="key-val"
rel="4774806"
href="https://bugs.openjdk.java.net/browse/JDK-8077056">JDK-8077056</a><br>
<br>
Thanks,<br>
Dima </blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
<br>
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