MinHeapFreeRatio / MaxHeapFreeRatio

[Jon Masamitsu]

Damon,

Do you turn on ExplicitGCInvokesConcurrent?

Jon

On 5/8/2012 11:47 PM, Damon Hart-Davis wrote:
> Hi,
>
> Note: I should have been clear that memory is not given back to the OS even when the heap is (say) 60%+ free and I force GCs.
>
> Rgds
>
> Damon
>
>
> On 9 May 2012, at 06:46, Damon Hart-Davis 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
>>
> _______________________________________________
> hotspot-gc-use mailing list
> hotspot-gc-use at openjdk.java.net
> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use