MinHeapFreeRatio / MaxHeapFreeRatio

[Damon Hart-Davis]

Hi,

Interesting!

Is that likely to be a good idea on a uniprocessor, and have you been using it with concgc/incgc?

Rgds

Damon


On 21 May 2012, at 16:18, Carfield Yim wrote:

> HI, I have to include -XX:+UseParNewGC if I need MaxHeapFreeRatio
> working, maybe you can try on it.
> 
> On Wed, May 9, 2012 at 1:46 PM, Damon Hart-Davis <dhd at exnet.com> wrote:
>> Hi,
>> 
>> First time on this list, so hello!  I see a few familiar names from days of yore!
>> 
>> I am running my favourite (Tomcat/Web) app in a very constrained memory environment (a SheevaPlug) along with all the usual Internet server junk (sendmail,  ntp, sshd, etc) and I am aiming to squeeze it into the even tighter space of a Raspberry Pi in due course.
>> 
>> As such, I want the JVM to give memory back to the OS whenever possible.  In code I set a target to keep about 25% of the heap free, and so for example I stop cacheing some stuff when below that, and cache more vigorously above that.
>> 
>> Here are some relevant options:
>> 
>> CATALINA_OPTS="-Xmx100m -Xms64m"
>> # Cap size of non-(main-)heap components.
>> CATALINA_OPTS="$CATALINA_OPTS -XX:MaxPermSize=48m"
>> # Trim thread stack size.
>> CATALINA_OPTS="$CATALINA_OPTS -Xss256k"
>> # Keep the new generation well within the target 25% free...
>> CATALINA_OPTS="$CATALINA_OPTS -XX:NewRatio=5"
>> # Be aggressive about giving memory back to the system above target 25% free.
>> CATALINA_OPTS="$CATALINA_OPTS -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=26"
>> # Run in incremental GC mode to minimise pauses.
>> CATALINA_OPTS="$CATALINA_OPTS -Xincgc"
>> 
>> I see some evidence that the free ratios are being observed by when the heap is expanded, but I have never seen any variant of JDK 6 or 7, including the Oracle embedded 6, actually give memory back to the OS with this app.
>> 
>> Am I still doing something wrong?  B^>
>> 
>> Rgds
>> 
>> Damon
>> 
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>