OpenJDK Contributions

[Doerr, Martin]

Hi Archana,

thanks for posting your proposals. I appreciate getting J9 improvements into OpenJDK.

About Contribution 1:
I'm not so familiar with the AIX implementation of malloc, but I wonder if "multiheap" leads to similar memory footprint issues as on linux with glibc:
https://bugs.openjdk.java.net/browse/JDK-8193521
At least "multiheap" sounds similar to MALLOC_ARENA_MAX (glibc). It may be good for J9, but we need a separated performance and footprint evaluation for OpenJDK. I don't know which workload would benefit from it. I guess we don't have many concurrent mallocs in performance critical paths in hotspot.

Using 64kB pages makes a lot of sense to me. I believe we're already using them to some extent.
I'm only a bit concerned about 64kB stack pages because we still have the stack banging implementation which establishes protected "yellow" and "red" pages. Maybe we should remove the stack banging code before using 64kB stack pages.

About Contribution 2:
I wonder why we're not using it already. Technically, makes sense to me. However, it may trigger existing bugs with large addresses.
(See https://stackoverflow.com/questions/2288728/drawbacks-of-using-largeaddressaware-for-32-bit-windows-executables)
We're still building Windows 32 bit, but we're no longer using it with recent jdk/jdk. Maybe somebody is interested in having it and can test and review it.

Just my 5C.

Best regards,
Martin


> -----Original Message-----
> From: jdk-dev <jdk-dev-retn at openjdk.java.net> On Behalf Of Archana
> Nogriya
> Sent: Montag, 7. September 2020 11:10
> To: jdk-dev at openjdk.java.net; jdk-dev-request at openjdk.java.net
> Cc: Andrew Leonard <andrew_m_leonard at uk.ibm.com>
> Subject: OpenJDK Contributions
> 
> Hi,
> 
> I am requesting 2 proposals for the contribution to OpenJDK.
> I have created webrev with my changes.
> 
> Please can I have someone to review my changes and suggest further.
> 
> Details description is as follow,
> 
> Contribution 1
> 
> =======================================
> Title : Performance optimisation by setting MALLOCOPTIONS and LDR_CNTRL
> java launcher in order to use 64KB pages by default for perf on AIX.
> Description: The malloc subsystem provides an optional multiheap
> capability to allow the use of multiple heaps of free memory, rather than
> just one, to improve performance this is the fix . Also to setting
> LDR_CNTRL on AIX java launcher in order to use 64KB pages by default for
> perf.
> Changed File:
> http://hg.openjdk.java.net/jdk/jdk/file/5aeebd3bb33a/src/java.base/unix/n
> ative/libjli/java_md.c
> Webrev url: https://bugs.openjdk.java.net/browse/JDK-8252802
> =============================================
> 
> 
> Contribution 2
> 
> ==================================================
> Title : Add the /LARGEADDRESSAWARE flag when linking executables for
> Windows 32-bit.
> Description: The following change to add the /LARGEADDRESSAWARE flag
> when
> linking executables for Windows 32-bit. This simple change allows java to
> use more than 2GB address space. IBM Java uses this flag.
> Changed File:
> http://hg.openjdk.java.net/jdk/jdk/file/5aeebd3bb33a/make/autoconf/spe
> c.gmk.in
> Webrev url: https://bugs.openjdk.java.net/browse/JDK-8252803
> ==================================================
> 
> 
> Many Thanks & Regards
> Archana Nogriya
> Java Runtimes Development and Project Manager
> IBM Hursley
> IBM United Kingdom Ltd
> internet email: archana.nogriya at uk.ibm.com
> 
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
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