RFR(xs): 8202772: NMT erroneously assumes thread stack boundaries to be page aligned

[Lindenmaier, Goetz]

Hi Thomas, 

looks good.

Best regards,
  Goetz.

> -----Original Message-----
> From: hotspot-runtime-dev [mailto:hotspot-runtime-dev-
> bounces at openjdk.java.net] On Behalf Of Thomas Stüfe
> Sent: Dienstag, 12. Juni 2018 06:59
> To: Hotspot dev runtime <hotspot-runtime-dev at openjdk.java.net>
> Subject: RFR(xs): 8202772: NMT erroneously assumes thread stack
> boundaries to be page aligned
> 
> Dear all,
> 
> may I please have reviews for this fix, which - for now - disables
> thread stack tracking for NMT on AIX.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8202772
> Webrev: http://cr.openjdk.java.net/~stuefe/webrevs/8202772-NMT-
> erroneously-assumes-thread-stack-boundaries-to-be-page-
> aligned/webrev.00/webrev/
> 
> On AIX, we have two problems:
> 
> - NMT assumes stack boundaries to be page aligned. This is wrong but
> on all platforms other than AIX does not matter.
> - the way mincore() is used to read residency of pages needs to be
> adapted since on AIX, os::vm_page_size() is not necessarily the page
> size used by mincore() - which is quite dangerous.
> 
> Since JDK-8204552 was added to deal with the first point, it makes
> sense to wait until that issue is finished. Until then, I'd like to
> disable thread stack recognition in NMT for AIX. We can revisit this
> topic again once we can spare time for it and JDK-8204552 has been
> done.