RFR(s): 8189864: Provide an ascii map to visualize metaspace fragmentation

[Thomas Stüfe]

Hi Coleen, Goetz,

new webrev, rebased to the new jdk-hs repo.

http://cr.openjdk.java.net/~stuefe/webrevs/8189864-metaspace-map/webrev.01/webrev/

Nothing changed.

@Coleen, would you be able to sponsor this? Thanks a lot!

Kind Regards, Thomas

On Wed, Nov 1, 2017 at 8:20 AM, Thomas Stüfe <thomas.stuefe at gmail.com>
wrote:

> Hi Goetz,
>
> On Mon, Oct 30, 2017 at 1:49 PM, Lindenmaier, Goetz <
> goetz.lindenmaier at sap.com> wrote:
>
>> Hi Thomas,
>>
>> the change looks good and I know we have made good use of this
>> already.
>>
>> Can you look into the chunks? It could be useful to know that,
>> for example, a medium chunk is used by a  class loader, but
>> still mostly empty (i.e., empty but not free).  Well, there is no
>> third variant after lower and upper case,  but maybe empty
>> parts could be indicated in the line with the dots by 'e's (obviously
>> at the granularity of small chunks).
>>
>> Thanks,
>>   Goetz.
>>
>>
> thank you for the review!
>
> Indicating which chunks are filled to what degree can certainly be done.
> Question is how useful this is (see Zhengyu's work for
> https://bugs.openjdk.java.net/browse/JDK-8189688), because within chunks
> there is no fragmentation, so the in-chunk map could look rather
> unexciting. I will take a look when I am back next week.
>
> Kind Regards, Thomas
>
> > -----Original Message-----
>> > From: hotspot-runtime-dev [mailto:hotspot-runtime-dev-
>> > bounces at openjdk.java.net] On Behalf Of Thomas Stüfe
>> > Sent: Wednesday, October 25, 2017 6:52 AM
>> > To: hotspot-runtime-dev at openjdk.java.net
>> > Subject: RFR(s): 8189864: Provide an ascii map to visualize metaspace
>> > fragmentation
>> >
>> > Hi all,
>> >
>> > could I please have your thoughts and reviews for this enhancement:
>> >
>> > Issue:  https://bugs.openjdk.java.net/browse/JDK-8189864
>> > Webrev: http://cr.openjdk.java.net/~stuefe/webrevs/8189864-
>> > metaspace-map/webrev.00/webrev/
>> >
>> > At SAP, we added a something we call a metaspace map to the metaspace
>> > analysis functions. This is a very simple ASCII print of the metaspace
>> > layout. It shows the composition of the VirtualSpaceNodes on a chunk
>> basis.
>> > It facilitates examining fragmentation and has been proven useful when
>> > experimenting with the metaspace allocator.
>> >
>> > This change adds the map printing code and invokes it if a Metaspace OOM
>> > occurs and -Xlog:gc+metaspace+freelist=debug is active (in this case,
>> we
>> > already print out a bunch of things). We also may consider adding this
>> to
>> > NMT or as a jcmd addition, but I did not want to overload the patch.
>> >
>> > Example output looks like this (mind that this will only make sense
>> with a
>> > monospaced font). Dots indicate starts of chunks. Letters indicate chunk
>> > type - (H)umongous, (M)edium, (S)mall (X)specialized - with lower case
>> > letters indicating
>> > a free chunk, upper case letters indicating a chunk in use.
>> >
>> > 0x0000000100000000:   ......
>> >                       xxxxxxHHHHHHHHHHHHHHHHHHHHHHHH
>> > HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > HHHHHHHHH
>> > HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > 0x0000000100020000:
>> >                       HHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > HHHHHHHHH
>> > HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > 0x0000000100040000:
>> >                       HHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > HHHHHHHHH
>> > HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
>> > 0x0000000100060000:   . . . . . . . . . . . . . .
>> >                       SSSSSSSSSSSSMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMSSSSSSSSMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > M
>> > 0x0000000100080000:   . . . .
>> >                       MMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMmmmmmmmmmmmmmmmm
>> > mmmmmmmmmmmmmmmmMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > M
>> > 0x00000001000a0000:   . . . .
>> >                       MMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > M
>> > 0x00000001000c0000:   . . . .
>> >                       MMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMmmmmmmmmmmmmmmmm
>> > mmmmmmmmmmmmmmmmMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > M
>> > 0x00000001000e0000:   . . . .
>> >                       MMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > M
>> > 0x0000000100100000:   . . . . . . . . . . . . . . . . . . . . . . . .
>> >                       MMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMMMMSSSSMMMMMMMMMMMMM
>> > MMMMMMMMMMMMMMMMMMMSS
>> > SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
>> > 0x0000000100120000:   . . . . . . . . . . . . . . . . . . . . . . . . .
>> . .
>> > . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
>> .
>> >                       SSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
>> > SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
>> > SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
>> >
>> >
>> > Thank you!
>> >
>> > Thomas
>>
>
>