blocks|key|247915|text|JVM指定将在-XX:PermSize启动期间分配的初始大小。如有必要，JVM将分配给-XX:MaxPermSize。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|247916|entityMap^0|7|C|17|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>-XX:PermSize</code> specifies the initial size that will be allocated during startup of the JVM. If necessary, the JVM will allocate up to <code>-XX:MaxPermSize</code>.

blocks|key|244135|text|通过使用-XX:PermSize和-Xms等参数，您可以调优性能，例如，应用程序的启动。我最近没有看过它，但是几年前-Xms的默认值大约是32MB+(我想)，如果你的应用程序需要更多的内存，它会触发一系列的内存填充周期-完全垃圾收集-增加内存等等，直到它加载了它需要的一切。此周期可能不利于启动性能，因此立即分配所需的编号可以提高启动性能。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|244136|类似的循环也适用于永久生成。因此，调整这些参数可以改善启动(以及其他)。|244137|警告当涉及到内存分配，划分eden空间和老一代时，JVM有很多优化和智能，所以不要做像-Xms等于-Xmx或者-XX:PermSize等于-XX:MaxPermSize这样的事情，因为这会删除一些JVM可以应用于其分配策略的优化，从而降低你的应用程序的性能，而不是提高它。|BOLD|244138|一如既往:进行重要的测量以证明您的更改确实提高了整体性能(例如，在使用应用程序期间，改善启动时间可能会对性能造成灾难性的影响)|244139|entityMap^0|4|C|H|4|1M|4|0|0|0|2|17|4|1D|4|1J|C|1X|F|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|W|8|@$9|X|A|Y|B|J]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|K|3|L|5|6|7|17|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|N|$]]

By playing with parameters as <code>-XX:PermSize</code> and <code>-Xms</code> you can tune the performance of - for example - the startup of your application. I haven't looked at it recently, but a few years back the default value of <code>-Xms</code> was something like 32MB (I think), if your application required a lot more than that it would trigger a number of cycles of fill memory - full garbage collect - increase memory etc until it had loaded everything it needed. This cycle can be detrimental for startup performance, so immediately assigning the number required could improve startup.

A similar cycle is applied to the permanent generation. So tuning these parameters can improve startup (amongst others).

WARNING The JVM has a lot of optimization and intelligence when it comes to allocating memory, dividing eden space and older generations etc, so don't do things like making <code>-Xms</code> equal to <code>-Xmx</code> or <code>-XX:PermSize</code> equal to <code>-XX:MaxPermSize</code> as it will remove some of the optimizations the JVM can apply to its allocation strategies and therefor reduce your application performance instead of improving it.

As always: make non-trivial measurements to prove your changes actually improve performance overall (for example improving startup time could be disastrous for performance during use of the application)

blocks|key|3136107|text|如果您正在进行一些性能调优，通常建议将-XX:PermSize和-XX:MaxPermSize设置为相同的值，以提高JVM效率。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3136108|以下是一些信息：|3136109|3136110|Support+for+large+page+heap+on+x86+and+amd64+platforms|ordered-list-item|3136111|Java+Support+for+Large+Memory+Pages|3136112|Setting+the+Permanent+Generation+Size|3136113|3136114|如果使用的是CMS+GC，还可以指定-XX:%2BCMSClassUnloadingEnabled以启用类卸载选项。这可能有助于降低Java.lang.OutOfMemoryError:+PermGen+space的概率。|3136115|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/performance/reference/whitepapers/6_performance.html#2.1.4|1|http://www.oracle.com/technetwork/java/javase/tech/largememory-jsp-137182.html?ssSourceSiteId=ocomen|2|http://wikis.oracle.com/display/CommSuite/Convergence%2BPerformance%2BTuning#ConvergencePerformanceTuning-SettingthePermanentGenerationSize^0|J|C|W|F|1M|3|0|0|0|0|1I|0|0|0|Z|1|0|0|11|2|0|0|6|3|A|2|I|T|1S|15|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1B|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|1D|8|@]|D|@$9|1E|A|1F|1|1G]]|E|$]]|$1|L|3|M|5|K|7|1H|8|@]|D|@$9|1I|A|1J|1|1K]]|E|$]]|$1|N|3|O|5|K|7|1L|8|@]|D|@$9|1M|A|1N|1|1O]]|E|$]]|$1|P|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1Q|8|@$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]|$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1Z|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]|10|$5|V|W|X|E|$Y|11]]|12|$5|V|W|X|E|$Y|13]]]]

If you're doing some performance tuning it's often recommended to set both <code>-XX:PermSize</code> and <code>-XX:MaxPermSize</code> to the same value to increase <code>JVM</code> efficiency.

Here is some information:

<ol>
<li><a href="http://java.sun.com/performance/reference/whitepapers/6_performance.html#2.1.4" rel="noreferrer">Support for large page heap on x86 and amd64 platforms</a></li>
<li><a href="http://www.oracle.com/technetwork/java/javase/tech/largememory-jsp-137182.html?ssSourceSiteId=ocomen" rel="noreferrer">Java Support for Large Memory Pages</a></li>
<li><a href="http://wikis.oracle.com/display/CommSuite/Convergence+Performance+Tuning#ConvergencePerformanceTuning-SettingthePermanentGenerationSize" rel="noreferrer">Setting the Permanent Generation Size</a></li>
</ol>

You can also specify <code>-XX:+CMSClassUnloadingEnabled</code> to enable class unloading
option if you are using <code>CMS</code> <code>GC</code>. It may help to decrease the probability of <code>Java.lang.OutOfMemoryError: PermGen space</code>

We've run into a Java.lang.OutOfMemoryError: PermGen space error and looking at the tomcat JVM params, other than the <code>-Xms</code> and <code>-Xmx</code> params we also specify <code>-XX:MaxPermSize=128m</code>. After a bit of profiling I can see occasionally garbage collection happening on the PermGen space saving it from running full.

My question is: other than increasing the <code>-XX:MaxPermSize</code> what would be the difference if I specify as well <code>-XX:PermSize</code>? I know the total memory then would be Xmx+maxPermSize but is there any other reason why <code>-XX:PermSize</code> should not be there when <code>-XX:MaxPermSize</code> is specified?

Please do share if you have real-world experience dealing with these JVM parameters.

ps. The JVM is HotSpot 64bit Server VM build 16.2-b04

-XX:MaxPermSize with or without -XX:PermSize

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我们遇到了Java.lang.OutOfMemoryError: PermGen空间错误，在查看tomcat JVM参数时，除了-Xms和-Xmx参数之外，我们还指定了-XX:MaxPermSize=128m。经过一些分析之后，我可以看到在PermGen空间上偶尔会发生垃圾收集，从而使其免于满负荷运行。我的问题是:如果...

问使用或不使用-XX:PermSize的-XX:MaxPermSize
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