RFR(xxxs): 8204164: OOM-only logging in Metaspace

Thomas Stüfe thomas.stuefe at gmail.com
Fri Jun 1 06:00:45 UTC 2018

On Fri, Jun 1, 2018 at 12:22 AM, David Holmes <david.holmes at oracle.com> wrote:
> On 1/06/2018 6:37 AM, coleen.phillimore at oracle.com wrote:
>> I agree, this seems good, and fine with me to remove freelist.
> Have we established any policy for lifecycle management of logging tags? If
> you just rip out a tag and someone has a special logging script they run
> occasionally if they need to gather specific information, then they suddenly
> get a failure because someone decided "naw don't need that tag".

good point. Just tested, I would have expected UL to silently ignore
an invalid logging tag, or write a warning and go on, but it gives me
an error and exits. This I find overly harsh.

For me, this may mean that I will remove the tags from the metaspace
logging points - since I am sick of typing
"-Xlog:gc+metaspace+freelist" and asking myself each time "why
freelist?" (and for that matter, "why gc"? since most log points have
nothing to do with gc),  - but for now keep the tag in logTags.hpp.

I think the process surrounding UL tags is lacking, for both
introduction and deprecation of tags. There is no guideline of how
tags are to be named and how they should be introduced, or how they
should be deprecated .

Notice how tags are named with very short words. These words are in
itself a resource. So someone adding e.g. "age" or "start" or "cpu"
decides for the future what these tags mean. Since there is no
documentation whatsoever what these tags mean and under which
circumstances I can reuse them, I cannot reuse them.

Well, maybe its me, and I do not understand that part of UL. When
looking at UL first I thought, oh nice I can enable log points by
keywords like I would search for records in a database, but that seems
not at all what the authors had in mind. It seems the words are to be
used to form sentences? I never really got that part.


p.s. Since I have my two reviewers I still go forward with "8204164:
OOM-only logging in Metaspace". For the record, I introduced the new
tag "oom" and everyone is invited to use it to tag oom scenarios, not
just metaspace.

> David
> -----
>> Coleen
>> On 5/31/18 3:35 PM, Gerard Ziemski wrote:
>>> hi Thomas,
>>> Your enhancement looks useful to me.
>>> Removing “freelist” tag from “metaspace” seems worthy of a separate
>>> issue/discussion.
>>> cheers
>>>> On May 31, 2018, at 6:36 AM, Thomas Stüfe <thomas.stuefe at gmail.com>
>>>> wrote:
>>>> Hi all,
>>>> very tiny improvement. The intent is to be able to restrict metaspace
>>>> logging to OOM situations.
>>>> CR: OOM-only logging in Metaspace
>>>> Webrev:
>>>> http://cr.openjdk.java.net/~stuefe/webrevs/8204164-oom-only-logging-in-metaspace/webrev.00/webrev/
>>>> --
>>>> On a related note, would anyone be offended if I were to remove the
>>>> "freelist" logging tag from the metaspace coding? I am not sure that
>>>> is useful in any way.
>>>> Thanks, Thomas

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