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

[Hohensee, Paul]

Sorry about the formatting, I thought it did follow the guidelines, but I see now that I missed two things, the subject line and the list of backport approvers. I'll repost.

Thanks,

Paul

On 10/24/18, 8:17 AM, "Seán Coffey" <sean.coffey at oracle.com> wrote:

    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
    >                  
    >                  
    >                  
    >              
    >              
    >          
    >          
    >      
    >      
    >