[11u] Backport JEP 346 : Promptly Return Unused Committed Memory from G1

[Ruslan Synytsky]

*> Goetz: I understand the stability concerns. We are doing support for
Java for roughly 15 years now. But I think this is a rather small change,
only a few 100 lines! http://hg.openjdk.java.net/jdk/jdk/rev/f94c7929a44b
<http://hg.openjdk.java.net/jdk/jdk/rev/f94c7929a44b>. > Thus, the risk of
this change cannot be compared with downporting a whole GC algorithm, the
graal compiler or similar. We should not be misled by this being a JEP. *

*> Liang: BTW, the main feature is guarded by a separate option
G1PeriodicGCInterval and won't affect the default flow.*

Good points. As a summary, it's not a large code base adjustment which does
not change the default behaviour of JVM.

*> **Andrew: **We'd then put it out and get people to test it in real
applications, then very carefully merge it back into mainline. The problem
with this plan, of course, is that it's very hard in practice to get people
to use experimental releases in production! This is the perennial problem
with Beta testing, as we all know.*

*> Goetz:  we would volunteer to test the required changes in our
infrastructure and push it to SapMachine before they are brought to the
OpenJDK 11u-dev repository. It could run productive with SapMachine for one
update or so to collect feedback.*

>From Jelastic side, we can run full set of our functional, integration and
load tests related to provisioning and scaling of Java stacks.

*> **Andrew: **A question for you. Do you believe that there should be a
version of **JDK 11 which does not change very much, except for occasional
fixes **for remaining bugs?*
> *Liang: Actually JDK11u is not so widely used and most of users are still
using JDK8u. Migrating JDK versions is so painful to them that most of
users will not catch up latest versions for new features. An LTS version
with evolved updates is always the best choice. *

While I expected that migration to the new releases will be faster, we
notice the same issue described by Liang among our Java end users.

*> Alexey: **Bottom-line: it is not about the technical feasibility of the
backport and initial testing -- that one is doable and pretty clear. What
happens next is where the problem is.*
*> Goetz: Also, we as part of the 11u maintenance team will take our part
to address upcoming issues with this change.*
*> Liang: We Alibaba will surely take the responsibility of maintenance as
well.*

Is this commitment enough for making steps forward? Are there any other
unspoken or uncovered important questions?

Thanks
-- 
Ruslan Synytsky
CEO @ Jelastic Multi-Cloud PaaS <https://jelastic.com/>