Thank you very much, Ioi!
- Jini.
On 12/10/2018 12:01 PM, Ioi Lam wrote:
Hi Jini,
These changes look good to me. Thanks!
- Ioi
On 12/7/18 11:22 AM, 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 :-(
http://openjdk.5641.n7.nabble.com/RFR-S-JDK-8200613-SA-jstack-throws-UnmappedAddressException-with-a-CDS-core-file-td352681.html#a353026
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: http://cr.openjdk.java.net/~jgeorge/8200613/webrev.01/
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.
