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List: openjdk-hotspot-runtime-dev
Subject: Re: RFR: (S): JDK-8200613: SA: jstack throws UnmappedAddressException with a CDS core file
From: Jini George <jini.george () oracle ! com>
Date: 2018-12-12 4:59:38
Message-ID: e80778b1-d805-450f-e91b-ac027c761a53 () oracle ! com
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Thank you, Coleen!
-Jini.
On 12/12/2018 12:58 AM, coleen.phillimore@oracle.com wrote:
>
>
> On 12/11/18 2:37 AM, Jini George wrote:
> > Thank you very much, Coleen. I have converted the flag into a
> > diagnostic flag. The revised webrev is at:
> >
> > http://cr.openjdk.java.net/~jgeorge/8200613/webrev.03/
>
> Looks great!
> >
> > A plain diff between this patch and the earlier one is at:
> >
> > http://cr.openjdk.java.net/~jgeorge/8200613/incremental_diff
> >
> > I will withdraw the associated CSR.
>
> Yes, please withdraw it. Thank you!
>
> Coleen
>
> >
> > Thanks!
> > Jini.
> >
> > On 12/10/2018 11:55 PM, coleen.phillimore@oracle.com wrote:
> > >
> > > I see. In this case, the flag should be diagnostic and not require a
> > > CSR. I suppose some documentation should be added so that sustaining
> > > will know about the option in this case (Hi Kevin!)
> > >
> > > thanks,
> > > Coleen
> > >
> > >
> > > On 12/10/18 1:38 AM, Ioi Lam wrote:
> > > > Hi Coleen,
> > > >
> > > > I was one of the people who suggested the DumpPrivateMappingsInCore
> > > > flag. It's enabled by default, so by default all the contents of
> > > > mmap'ed files with MAP_PRIVATE will be saved to the core files.
> > > >
> > > > The worry is, there may be some extreme cases where the JVM has
> > > > mapped very large files (with NIO or JNI, etc). For example, you
> > > > could have a 100GB in-memory database. For those cases, if the user
> > > > is experiencing crashes, but they are unable to get a core dump
> > > > (because it would be too large), they can try running with
> > > > -XX:-DumpPrivateMappingsInCore.
> > > >
> > > > Thanks
> > > >
> > > > - Ioi
> > > >
> > > >
> > > > On 12/7/18 12:03 PM, coleen.phillimore@oracle.com wrote:
> > > > >
> > > > > Hi Jini, We were just talking about this new option. If someone
> > > > > gets a crash, I don't think they're going to run their application
> > > > > again with -XX:-DumpPrivateMappingsInCore in the case of the core
> > > > > file being too large. So I don't know how generally useful this
> > > > > option is. I think it would be better to not add it and set the bit
> > > > > to include the mappings unconditionally.
> > > > >
> > > > > How much larger is this core file (we had trouble understanding
> > > > > from the bug)? If you need the mappings to understand and use the
> > > > > SA tools on it, we want to have them.
> > > > >
> > > > > Thanks,
> > > > > Coleen
> > > > >
> > > > >
> > > > > On 12/7/18 2:22 PM, Jini George wrote:
> > > > > > I have the revised webrev here:
> > > > > >
> > > > > > http://cr.openjdk.java.net/~jgeorge/8200613/webrev.02/index.html
> > > > > >
> > > > > > The extra changes here are to:
> > > > > >
> > > > > > * Introduce a new option DumpPrivateMappingsInCore to control the
> > > > > > dumping of the file backed private regions into the corefile.
> > > > > >
> > > > > > * Close the modules file before dumping core in os::abort().
> > > > > > Currently, there is a small bug
> > > > > > (https://bugs.openjdk.java.net/browse/JDK-8215026) which prevents
> > > > > > the closure of the image file in unmapping the entire file.
> > > > > >
> > > > > > I plan to take up the unmapping of NIO MapMode.PRIVATE files as a
> > > > > > separate task (https://bugs.openjdk.java.net/browse/JDK-8215027)
> > > > > > since this seems a bit involved.
> > > > > >
> > > > > > Thanks a bunch,
> > > > > > Jini.
> > > > > >
> > > > > > On 11/12/2018 10:26 AM, Jini George wrote:
> > > > > > > Thank you very much, Chris, Kevin and Ioi for your comments!
> > > > > > >
> > > > > > > I will send another webrev with this change enabled under an
> > > > > > > opt-out flag, as you suggest, and would look at unmapping the JDK
> > > > > > > modules file and if possible, the NIO mapped files too in the
> > > > > > > signal handler.
> > > > > > >
> > > > > > > Thanks a bunch,
> > > > > > > Jini.
> > > > > > >
> > > > > > > On 11/9/2018 11:53 PM, Ioi Lam wrote:
> > > > > > > > Hi Jini,
> > > > > > > >
> > > > > > > > Thanks for investigating the size expansion issue.
> > > > > > > >
> > > > > > > > I agree that the size increase is worth it. Even when not using
> > > > > > > > SA, if we open the core file inside GDB, we cannot read certain
> > > > > > > > sections in the CDS archive (such as the RO section and strings
> > > > > > > > sections). That would make debugging difficult. So I am in favor
> > > > > > > > of this change.
> > > > > > > >
> > > > > > > > For the JDK modules file, maybe we can unmap it in the signal
> > > > > > > > handler, before going ahead with the core dump? I think it's
> > > > > > > > hardly needed for debugging purposes. (Perhaps we can also do
> > > > > > > > the same for the NIO mapped files?)
> > > > > > > >
> > > > > > > > A opt-flag as suggested by Kevin is a good idea.
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > >
> > > > > > > > - Ioi
> > > > > > > >
> > > > > > > > On 11/9/18 3:29 AM, Kevin Walls wrote:
> > > > > > > > > Hi Jini,
> > > > > > > > >
> > > > > > > > > Looks good to me. It might be a significant increase in size
> > > > > > > > > of _some_ core files, but so many core files we see are much
> > > > > > > > > larger, in gigabytes++ of course, so the CDS data size should
> > > > > > > > > not be such a significant increase on (I think) most files.
> > > > > > > > >
> > > > > > > > > The flexibiity of always having the CDS data there is very
> > > > > > > > > significant. A core file should ideally be usable, without
> > > > > > > > > additionally requiring the CDS archive from the machine. That
> > > > > > > > > additional human round-trip upload request on every transmitted
> > > > > > > > > core that needs investigating, seems like a less efficient
> > > > > > > > > route...).
> > > > > > > > >
> > > > > > > > > Is there an opt-out? It's conditional on UseSharedSpaces but
> > > > > > > > > could there be a flag to disable, in case we see crashes with
> > > > > > > > > gigabytes of private mappings that we really don't want to
> > > > > > > > > retain (the user would have to know to set a flag, to disable
> > > > > > > > > the new coredump filter ahead of time).
> > > > > > > > >
> > > > > > > > > Thanks!
> > > > > > > > > Kevin
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On 29/10/2018 06:02, Jini George wrote:
> > > > > > > > > > Thank you very much, Ioi, for looking into this, and the
> > > > > > > > > > clarification offline. My bad, I had missed the earlier mail
> > > > > > > > > > from you. :-( My responses below.
> > > > > > > > > >
> > > > > > > > > > Yes, I had tested this on MacOS. The issue does not exist on
> > > > > > > > > > MacOS since the file backed private mmap()-ed regions get
> > > > > > > > > > dumped into the MacOS corefiles by default.
> > > > > > > > > >
> > > > > > > > > > The corefile sizes on Linux do increase due to this change.
> > > > > > > > > > And the increase would also include any file mapped using NIO
> > > > > > > > > > with MapMode.PRIVATE. The typical corefile size increase with
> > > > > > > > > > this change would include the following components at a high
> > > > > > > > > > level:
> > > > > > > > > >
> > > > > > > > > > * Any NIO file mapping with MapMode.PRIVATE.
> > > > > > > > > > * Any file mmap()-ed by any native library with MAP_PRIVATE.
> > > > > > > > > > * The read only CDS regions (ro and od): Of the order of a few
> > > > > > > > > > MB.
> > > > > > > > > > * The shared strings CDS region. (typically less than 1 MB).
> > > > > > > > > > * 2 MB per native shared library (regions with ---p
> > > > > > > > > > permissions mapped by the dynamic linker for better alignment
> > > > > > > > > > and for keeping libraries efficiently shareable).
> > > > > > > > > > * The JDK 'modules' file. (About 140 MB).
> > > > > > > > > >
> > > > > > > > > > So, without including any NIO mapping, I typically see around
> > > > > > > > > > 250-300 MB increase in the corefile sizes. I agree that the
> > > > > > > > > > size increase could be a cause for concern, but for FWIW,
> > > > > > > > > > these privately mapped files get dumped into the corefile for
> > > > > > > > > > MacOS too. And the corefile sizes for the same program on
> > > > > > > > > > MacOS are way larger (of the order of a few GB as against
> > > > > > > > > > about 300 MB on Linux (without the change)).
> > > > > > > > > >
> > > > > > > > > > The advantage of fixing this by modifying the coredump_filter
> > > > > > > > > > v/s doing it in SA (by reading in more sections of the shared
> > > > > > > > > > archive file) is that this would benefit other debuggers like
> > > > > > > > > > gdb also. (And reduces the dependence on having the shared
> > > > > > > > > > archive file being available at the time of debugging). If
> > > > > > > > > > folks still think this is a cause for concern, I could make
> > > > > > > > > > modifications to fix this by reading in the regions from the
> > > > > > > > > > shared archive file in the SA code. I also wonder if it is
> > > > > > > > > > worth taking a relook at the mapping types of the various CDS
> > > > > > > > > > regions also.
> > > > > > > > > >
> > > > > > > > > > Thank you,
> > > > > > > > > > Jini.
> > > > > > > > > >
> > > > > > > > > > On 10/22/2018 10:27 AM, Ioi Lam wrote:
> > > > > > > > > > > Hi Jini,
> > > > > > > > > > >
> > > > > > > > > > > Did you see my earlier reply? I might have sent it out during
> > > > > > > > > > > the mail server outage days :-(
> > > > > > > > > > >
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> > > > > > > > > > >
> > > > > > > > > > > Here was my reply again:
> > > > > > > > > > >
> > > > > > > > > > > > Hi Jini,
> > > > > > > > > > > >
> > > > > > > > > > > > The changes looks good to me.
> > > > > > > > > > > >
> > > > > > > > > > > > Have you tested this on MacOS? CDS heap support is also
> > > > > > > > > > > > enabled on
> > > > > > > > > > > > MacOS. See macros.hpp:
> > > > > > > > > > > >
> > > > > > > > > > > > #if INCLUDE_CDS && INCLUDE_G1GC && defined(_LP64) &&
> > > > > > > > > > > > !defined(_WINDOWS)
> > > > > > > > > > > > #define INCLUDE_CDS_JAVA_HEAP 1
> > > > > > > > > > > >
> > > > > > > > > > > > Also, besides CDS, do we know how often other files will be
> > > > > > > > > > > > mmaped with
> > > > > > > > > > > > MAP_PRIVATE? Will users get huge core files because CDS is
> > > > > > > > > > > > enabled? In
> > > > > > > > > > > > JDK 12, CDS will be enabled by default (see JDK-8202951), so
> > > > > > > > > > > > all users
> > > > > > > > > > > > will be affected by the following line:
> > > > > > > > > > > >
> > > > > > > > > > > > if (UseSharedSpaces) {
> > > > > > > > > > > > set_coredump_filter(FILE_BACKED_PVT_BIT);
> > > > > > > > > > > > }
> > > > > > > > > > > >
> > > > > > > > > > > > Maybe you can run an big app such as Eclipse, trigger a core
> > > > > > > > > > > > dump, and
> > > > > > > > > > > > compare the size of the core file before/after this change?
> > > > > > > > > > > >
> > > > > > > > > > > > Thanks
> > > > > > > > > > > >
> > > > > > > > > > > > - Ioi
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > Thanks
> > > > > > > > > > >
> > > > > > > > > > > - Ioi
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > On 10/21/18 8:58 PM, Jini George wrote:
> > > > > > > > > > > > Gentle reminder!
> > > > > > > > > > > >
> > > > > > > > > > > > Thanks,
> > > > > > > > > > > > - Jini
> > > > > > > > > > > >
> > > > > > > > > > > > On 10/9/2018 11:31 AM, Jini George wrote:
> > > > > > > > > > > > > Hello!
> > > > > > > > > > > > >
> > > > > > > > > > > > > [Including runtime-dev since the changes are in runtime \
> > > > > > > > > > > > > code]
> > > > > > > > > > > > > Requesting reviews for:
> > > > > > > > > > > > >
> > > > > > > > > > > > > Webrev: \
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> > > > > > > > > > > > > \
> > > > > > > > > > > > > BugID: https://bugs.openjdk.java.net/browse/JDK-8200613
> > > > > > > > > > > > >
> > > > > > > > > > > > > Issue: jhsdb jstack would throw an UnmappedAddressException \
> > > > > > > > > > > > > with a core file generated from a CDS enabled java \
> > > > > > > > > > > > > process. This is seen only with Linux and with G1GC, while \
> > > > > > > > > > > > > trying to read in data from the shared strings region (the \
> > > > > > > > > > > > > closed archive heap space). This region (which is a file \
> > > > > > > > > > > > > backed private memory region) is not dumped into the \
> > > > > > > > > > > > > corefile for Linux. This, being a heap region (and \
> > > > > > > > > > > > > therefore being a read-write region) is also not read in \
> > > > > > > > > > > > > from the classes.jsa file in SA since only the read only \
> > > > > > > > > > > > > regions are read in while processing the core file. (The \
> > > > > > > > > > > > > expectation being that the read write regions are in the \
> > > > > > > > > > > > > core file).
> > > > > > > > > > > > > Proposed solution: The proposed solution is to have the
> > > > > > > > > > > > > coredump_filter value corresponding to the CDS process to
> > > > > > > > > > > > > include bit 2 (file-backed private memory), so that the
> > > > > > > > > > > > > file-backed private memory region also gets dumped into the \
> > > > > > > > > > > > > corefile. The proposed fix is in
> > > > > > > > > > > > > src/hotspot/os/linux/os_linux.cpp.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Thanks,
> > > > > > > > > > > > > Jini.
> > > > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > >
> > > >
> > >
>
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