Backport 8195115: G1 Old Gen MemoryPool CollectionUsage.used values don't reflect mixed GC results

[Seán Coffey]

I wasn't aware of a pending approval request given that the mail doesn't 
follow approval guidelines [1]

This fix has implications on behaviour in an update release. We should 
get Joe Darcy's approval before backporting.

Joe - what are your recommendations ?

regards,
Sean.

[1] http://openjdk.java.net/projects/jdk8u/approval-template.html

Regards,
Sean.

On 24/10/18 15:40, Hohensee, Paul wrote:
> Ping. Is there anything I've left out from the request?
>
> Thanks,
>
> Paul
>
> On 10/22/18, 12:21 PM, "jdk8u-dev on behalf of Hohensee, Paul" <jdk8u-dev-bounces at openjdk.java.net on behalf of hohensee at amazon.com> wrote:
>
>      Typo, webrev s/b webrev.05.
>      
>      JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8195115
>      Webrev: http://cr.openjdk.java.net/~phh/8195115/webrev.05/
>      Backport review thread: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-October/023507.html
>      Original review thread: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-June/022305.html
>      
>      On 10/22/18, 8:45 AM, "jdk8u-dev on behalf of Hohensee, Paul" <jdk8u-dev-bounces at openjdk.java.net on behalf of hohensee at amazon.com> wrote:
>      
>          Trying again with correct request template.
>          
>          JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8195115
>          Webrev: http://cr.openjdk.java.net/~phh/8195115/webrev.06/
>          Backport review thread: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-October/023507.html
>          Original review thread: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-June/022305.html
>          
>          Thanks,
>          
>          Paul
>          
>          On 10/19/18, 10:11 AM, "jdk8u-dev on behalf of Hohensee, Paul" <jdk8u-dev-bounces at openjdk.java.net on behalf of hohensee at amazon.com> wrote:
>          
>              Thanks, Thomas. Cutting distribution down to jdk8u-dev now, and asking for backport approval.
>              
>              Here's the email discussion: http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-June/022305.html
>              
>              Backport argument:
>              
>              At Amazon, we discovered more than a year ago that the MemoryPoolMXBean Usage attribute isn't very useful for monitoring, and more importantly, alarming on, excessive heap use. That's because it's an instantaneous measurement, so it includes yet-to-collected garbage. We moved to using CollectionUsage (usage after the last GC that affected the memory pool) instead as a measure of the long-term heap occupancy. If it's trending up without the app changing, there may be a memory leak, or just more load that might require a -Xmx increase.
>              
>              Once moved, however, we found that G1 was effectively useless to us because it reported incorrect values for the G1 old gen: mixed collections weren't updating its CollectionUsage. We patched our internal jdk8 distro, and last June, openjdk11. This is a backport of the latter. We believe that anyone monitoring server apps running G1 in jdk8u needs this fix.
>              
>              Thanks,
>              
>              Paul
>              
>              On 10/19/18, 9:24 AM, "Thomas Schatzl" <thomas.schatzl at oracle.com> wrote:
>              
>                  Hi Paul,
>                  
>                  On Fri, 2018-10-12 at 00:03 +0000, Hohensee, Paul wrote:
>                  > Please review a backport to jdk8u.
>                  >
>                  > Bug: https://bugs.openjdk.java.net/browse/JDK-8195115
>                  > Webrev: http://cr.openjdk.java.net/~phh/8195115/webrev.05/
>                  > JDK11 patch: http://hg.openjdk.java.net/jdk/jdk/rev/5d3c5af82654
>                  >
>                  > The backport is slightly different from the JDK11 patch due to G1
>                  > refactoring, hence my request for new review. I’ll ask for jdk8u
>                  > approval once the backport is reviewed.
>                  
>                  > I backported two jtreg tests from JDK11, which pass. Also, all the
>                  > hotspot gc jtreg tests pass as well as they do for jdk8u-dev.
>                  
>                  I think the backport is good. Others need to decide whether this change
>                  is worth backporting.
>                  
>                  > There was a CSR involved,
>                  > https://bugs.openjdk.java.net/browse/JDK-8196719. Does that have to
>                  > be re-approved for jdk8u as well, and if so, what’s the process?
>                  
>                  CC'ed Joe Darcy as I am not sure either.
>                  
>                  Thanks,
>                    Thomas
>                  
>                  
>                  
>              
>              
>          
>          
>      
>      
>