FW: RFR (S): 8195115: G1 Old Gen MemoryPool CollectionUsage.used values don't reflect mixed GC results

[Erik Helin]

(adding back serviceability-dev, please keep both hotspot-gc-dev and 
serviceability-dev)

Hi Paul,

before I start re-reviewing, did you test the new version of the patch 
via the jdk/submit repository [0]?

Thanks,
Erik

[0]: http://hg.openjdk.java.net/jdk/submit

On 06/09/2018 03:29 PM, Hohensee, Paul wrote:
> Didn't seem to make it to hotspot-gc-dev...
> 
> On 6/8/18, 10:14 AM, "serviceability-dev on behalf of Hohensee, Paul" <serviceability-dev-bounces at openjdk.java.net on behalf of hohensee at amazon.com> wrote:
> 
>      Back after a long hiatus...
>      
>      Thanks, Eric, for your review. Here's a new webrev incorporating your recommendations.
>      
>      Bug: https://bugs.openjdk.java.net/browse/JDK-8195115
>      Webrev: http://cr.openjdk.java.net/~phh/8195115/webrev.02/
>      
>      TIA for your re-review. Plus, may I have another reviewer look at it please?
>      
>      Paul
>      
>      On 2/26/18, 8:47 AM, "Erik Helin" <erik.helin at oracle.com> wrote:
>      
>          Hi Paul,
>          
>          a couple of comments on the patch:
>          
>          - memoryService.hpp:
>             + 150                   bool countCollection,
>             + 151                   bool allMemoryPoolsAffected = true);
>          
>             There is no need to use a default value for the parameter
>             allMemoryPoolsAffected here. Skipping the default value also allows
>             you to put allMemoryPoolsAffected to TraceMemoryManager::initialize
>             in the same relative position as for the constructor parameter (this
>             will make the code more uniform and easier to follow).
>          
>          - memoryManager.cpp
>          
>             Instead of adding a default parameter, maybe add a new method?
>             Something like GCMemoryManager::add_not_always_affected_pool()
>             (I couldn't come up with a shorter name at the moment).
>          
>          - TestMixedOldGenCollectionUsage.java
>          
>             The test is too strict about how and when collections should
>             occur. Tests written this way often become very brittle, they might
>             e.g. fail to finish a concurrent mark on time on a very slow, single
>             core, machine. It is better to either force collections by using the
>             WhiteBox API or make the test more lenient.
>          
>          Thanks,
>          Erik
>          
>          On 02/22/2018 09:54 PM, Hohensee, Paul wrote:
>          > Ping for a review please.
>          >
>          > Thanks,
>          >
>          > Paul
>          >
>          > On 2/16/18, 12:26 PM, "serviceability-dev on behalf of Hohensee, Paul" <serviceability-dev-bounces at openjdk.java.net on behalf of hohensee at amazon.com> wrote:
>          >
>          >      The CSR https://bugs.openjdk.java.net/browse/JDK-8196719 for the original fix has been approved, so I’m back to requesting a code review, please.
>          >
>          >      Bug: https://bugs.openjdk.java.net/browse/JDK-8195115
>          >      Webrev: http://cr.openjdk.java.net/~phh/8195115/webrev.hs.01/
>          >
>          >      Passed a submit repo run, passes its jtreg test, and a JDK8 version is in production use at Amazon.
>          >
>          >      From the original RR:
>          >
>          >          > The bug is that from the JMX point of view, G1’s incremental collector
>          >          > (misnamed as the “G1 Young Generation” collector) only affects G1’s
>          >          > survivor and eden spaces. In fact, mixed collections run by this
>          >          > collector also affect the G1 old generation.
>          >          >
>          >          > This proposed fix is to record, for each of a JMX garbage collector's
>          >          > memory pools, whether that memory pool is affected by all collections
>          >          > using that collector. And, for each collection, record whether or not
>          >          > all the collector's memory pools are affected. After each collection,
>          >          > for each memory pool, if either all the collector's memory pools were
>          >          > affected or the memory pool is affected for all collections, record
>          >          > CollectionUsage for that pool.
>          >          >
>          >          > For collectors other than G1 Young Generation, all pools are recorded as
>          >          > affected by all collections and every collection is recorded as
>          >          > affecting all the collector’s memory pools. For the G1 Young Generation
>          >          > collector, the G1 Old Gen pool is recorded as not being affected by all
>          >          > collections, and non-mixed collections are recorded as not affecting all
>          >          > memory pools. The result is that for non-mixed collections,
>          >          > CollectionUsage is recorded after a collection only the G1 Eden Space
>          >          > and G1 Survivor Space pools, while for mixed collections CollectionUsage
>          >          > is recorded for G1 Old Gen as well.
>          >          >
>          >          > Other than the effect of the fix on G1 Old Gen MemoryPool.
>          >          > CollectionUsage, the only external behavior change is that
>          >          > GarbageCollectorMXBean.getMemoryPoolNames will now return 3 pool names
>          >          > rather than 2.
>          >          >
>          >          > With this fix, a collector’s memory pools can be divided into two
>          >          > disjoint subsets, one that participates in all collections and one that
>          >          > doesn’t. This is a bit more general than the minimum necessary to fix
>          >          > G1, but not by much. Because I expect it to apply to other incremental
>          >          > region-based collectors, I went with the more general solution. I
>          >          > minimized the amount of code I had to touch by using default parameters
>          >          > for GCMemoryManager::add_pool and the TraceMemoryManagerStats constructors.
>          >
>          >
>          >
>          
>      
>      
>