8201495: [Zero] Reduce limits of max heap size for boot JDK on s390

[Severin Gehwolf]

Hi Magnus,

On Mon, 2018-04-16 at 10:58 +0200, Magnus Ihse Bursie wrote:
> On 2018-04-13 15:40, Severin Gehwolf wrote:
> > Hi,
> > 
> > We (Red Hat) have been building Zero on s390 for a while now. In order
> > to do so we needed to have this patch to reduce the maximum heap size
> > setting for big workloads. Otherwise we see this during (JDK 9) builds:
> > 
> > ++ /usr/bin/tee /builddir/build/BUILD/java-9-openjdk-9.0.4.12-5.openjdk9.el7.s390/openjdk/build/jdk/modules/java.base/_the.java.base_batch.log
> > ++ /usr/bin/tee /builddir/build/BUILD/java-9-openjdk-9.0.4.12-5.openjdk9.el7.s390/openjdk/build/jdk/modules/java.base/_the.java.base_batch.log
> > Error occurred during initialization of VM
> > Could not reserve enough space for 1048576KB object heap
> > 
> > NOTE: JDK 9 has the same build logic than JDK 11 in terms of big
> > workloads' JVM switches.
> > 
> > Bug: https://bugs.openjdk.java.net/browse/JDK-8201495
> > webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8201495/webrev.01/
> 
> Hi Severin,
> 
> As I said in the bug report (didn't notice that you've already sent out 
> a webrev here), I'm not really fond of adding platforms guard if they 
> can be avoided. Normally, Java programs use more or less the same amount 
> of heap regardless of platforms they run on, differing only by platform 
> word size. So if a lower mx is enough on s390 builds, it's mostly likely 
> to be enough on all platforms, and thus the guard is unnecessary, and 
> will only make it harder to update the code in the future.
> 
> Also, the value of ms is typically of less concern. While mx is setting 
> an upper bound on resource allocation, ms is more of a "performance 
> hint" to the gc. Unless this is needed for your fix to work, I recommend 
> you leave it at it's current value.

Latest webrev:
http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8201495/webrev.02/

This now only changes -Xmx unconditionally and it bootcycle-builds
successfully on linux 32 bit, ppc (32 bit Zero) and s390 (32 bit Zero).

I haven't heard back from jdk-submit. It's radio silence since I've
pushed the branch. Not sure what's up with that.

Magnus, you've OK'ed the patch on the bug. Asking here again to
clarify. Is it OK to push this?

Thanks,
Severin

> /Magnus
> 
> > 
> > Testing: Run configure on s390 and inspected the big workloads settings:
> > 
> > Before:
> > checking flags for bootcycle boot jdk java command for big workloads... -Xms64M -Xmx998M -XX:ThreadStackSize=768
> > 
> > After:
> > checking flags for bootcycle boot jdk java command for big workloads... -Xms256M -Xmx768M -XX:ThreadStackSize=768
> > 
> > This should be fairly low risk, since the check is guarded by s390
> > archicture checks. Other architectures should be unaffected.
> > 
> > Thanks,
> > Severin
> 
>