RFR(M): 8190308: Supporting heap allocation on alternative memory devices and CSR review

[Kharbas, Kishor]

Greetings,

I am continuing the earlier discussion [1] with a revised issue number representing the implementation of the JEP [2].

I have addressed the remaining unaddressed comments (copied below) in these webrevs -
http://cr.openjdk.java.net/~kkharbas/8190308/webrev.11/
http://cr.openjdk.java.net/~kkharbas/8190308/webrev.11_to_10/

Also, I would appreciate a review of the CSR for the new flag at https://bugs.openjdk.java.net/browse/JDK-8190309.


> >  - in that same thread there has also been the question about the

> > need

> > for blocking the signals for the process that has gone unanswered.

> >



Removed the blocking of signals.



> >  - Arguments::finalize_vm_init_args: maybe at the place where the

> > change adds the warning/info message about NUMA support being

> > specific

> > to the file system; also add the same warning about UseLargePages

> > that

> > is located elsewhere.

> >

> > Like "UseXXXX may not be supported in some specific file system

> > implementations." - or just ignore as Andrew said in the other

> > email thread.

> >

> > Note that I am not sure that the selected place is the correct

> > place

> > for such warning about incompatible flags (and maybe

> > UseNUMA/UseLargePages should be forcibly disabled here? But then

> > again, it does not hurt just having it enabled?).

> >

> > I will let the runtime team comment as a lot of that argument

> > processing changed in jdk9.

> >

> > Maybe Arguments::check_vm_args_consistency() is better.

> >

> > There is similar code in Arguments::adjust_after_os()...

> >



1. Moved the check from finalize_vm_init_args() to check_vm_args_consistency()

2. When UseNUMA flag is true, adaptive logical group chunk resizing is used for Numa aware collectors such as ParallelOld. Just like UseNUMA is disabled in os::inti_2() in Linux when UseLargePages is set, it will be a good idea to disable UseNUMA when the new option is used.

3. I think its ok to leave UseNUMAInterleaving ON as it can be used for other memory areas.

4. For the same reason I also do not disable UseLargePages.

5. About handling UseLargePages, I thought of handling it the same way as when reserve_memory_special() fails to allocate large pages, i.e. generating a log_debug message.

      // failed; try to reserve regular memory below

  if (UseLargePages && (!FLAG_IS_DEFAULT(UseLargePages) ||

                        !FLAG_IS_DEFAULT(LargePageSizeInBytes))) {

    log_debug(gc, heap, coops)("Reserve regular memory without large pages");




> >  - here I may probably be speaking wrongly on behalf of the

> > runtime

> > team, but os.hpp, as an abstraction of the OS should probably not

> > have

> > platform specific ifdefs in it.

> >
and

> > > - You removed os::attempt_reserve_memory_at() from os.cpp and

> > > split

> > > into os_posix.cpp and os_windows.cpp.

> > >   But I think you should remain os::attempt_reserve_memory_at()

> > > at

> > > os.cpp and implement os specific stuffs at each os_xxx.cpp files

> > > for

> > > pd_xxx. Of cource move MemTracker function call as well.


In the updated webrev, I move the implementation from os_posix.cpp and os_window.cpp to respective pd_xxx functions. No AIX specific ifdef is required now.





Thank you and looking forward for your feedback.

- Kishor


[1] http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2017-October/020682.html
[2] https://bugs.openjdk.java.net/browse/JDK-8171181

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