RFR(xxs): 8187230: [aix] Leave OS guard page size at default for non-java threads instead of explicitly setting it

[Thomas Stüfe]

Hi Goetz,

thanks for the review!

Corrected webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8187230-aix-leave-os-guard-page-size-at-default-for-non-java-threads/webrev.01/webrev/

Thanks, Thomas


On Thu, Sep 7, 2017 at 2:20 PM, Lindenmaier, Goetz <
goetz.lindenmaier at sap.com> wrote:

> Hi Thomas,
>
> looks good except for that you missed setting the guard pages size to zero
> for compiler threads. Compiler threads are Java Threads and thus get
> our guard pages.
>
> Best regards,
>   Goetz.
>
> > -----Original Message-----
> > From: hotspot-dev [mailto:hotspot-dev-bounces at openjdk.java.net] On
> > Behalf Of Thomas Stüfe
> > Sent: Donnerstag, 7. September 2017 12:02
> > To: ppc-aix-port-dev at openjdk.java.net
> > Cc: HotSpot Open Source Developers <hotspot-dev at openjdk.java.net>
> > Subject: RFR(xxs): 8187230: [aix] Leave OS guard page size at default
> for non-
> > java threads instead of explicitly setting it
> >
> > Hi all,
> >
> > may I please have a review for this small change:
> >
> > Bug:
> > https://bugs.openjdk.java.net/browse/JDK-8187230
> >
> > Webrev:
> > http://cr.openjdk.java.net/~stuefe/webrevs/8187230-aix-
> > leave-os-guard-page-size-at-default-for-non-java-
> > threads/webrev.00/webrev/
> >
> > The change is very subtle.
> >
> > Before, we would set the OS guard page size for every thread - for java
> > threads disable them, for non-java threads we'd set them to 4K.
> >
> > Now, we still disable them for java threads but leave them at the OS
> > default size for non-java threads.
> >
> > The really important part is the disabling of OS guard pages for java
> > threads, where we have a VM guard pages in place and do not want to spend
> > more memory on OS guards. We do not really care for the exact size of the
> > OS guard pages for non-java threads, and therefore should not set it - we
> > should leave the size in place the OS deems sufficient. That also spares
> us
> > the complexity of handling the thread stack page size, which on AIX may
> be
> > different from os::vm_page_size().
> >
> > Thank you and Kind Regards, Thomas
>