RFR(S) 8189688: NMT: Report per-class load metadata information
Thomas Stüfe
thomas.stuefe at gmail.com
Wed Oct 25 05:00:50 UTC 2017
Hi Zhengyu,
On Tue, Oct 24, 2017 at 8:04 PM, Zhengyu Gu <zgu at redhat.com> wrote:
> Hi Thomas,
>
> On 10/24/2017 12:08 PM, Thomas Stüfe wrote:
>
>> Hi Zhengyu,
>>
>> - VM_PrintMetadata still has the _unit member, but I see it nowhere used.
>>
>> - I would have split the summary between class and non-class area, that
>> may have been more useful. But this is a matter of taste, I leave it up to
>> you.
>>
>> Agree, should go little further.
>
> Summary:
> Total class loaders= 754 capacity= 67528.00KB used= 61216.88KB
> free= 9453.11KB waste= 38.73KB
> Metadata capacity= 58780.00KB used= 54053.45KB
> free= 4726.55KB waste= 36.38KB
> Class data capacity= 8748.00KB used= 7163.43KB
> free= 1584.57KB waste= 2.35KB
>
> For anonymous classes= 580 capacity= 2732.00KB used= 1065.06KB
> free= 1666.94KB waste= 16.27KB
> Metadata capacity= 2152.00KB used= 738.46KB
> free= 1413.54KB waste= 16.27KB
> Class data capacity= 580.00KB used= 326.60KB
> free= 253.40KB waste= 0.00KB
>
>
>
Nice, thanks :)
> Updated webrev: http://cr.openjdk.java.net/~zgu/8189688/webrev.03/
>
>
All is well. Note that you could reduce the footprint of your change
somewhat by defining a structure like this:
struct numbers_t { size_t cap; size_t used; size_t free; size_t waste; }
and replacing the many members in PrintCLDMetaspaceInfoClosure with
instances of this structure:
numbers_t total;
numbers_t total_class;
numbers_t total_anon;
numbers_t total_anon_class;
Depending on how far you go, your code could deflate quite a bit. Give the
structure a default ctor and your large initializer list goes away; give it
a printing function and you reduce print-summary() to four function calls;
with something like an numbers_t::add(size_t cap, size_t used, size_t free,
size_t waste) you can reduce the additions in
PrintCLDMetaspaceInfoClosure::print_metaspace() to four lines.
Just a suggestion, I leave it up to you if you do this.
Lines 3108 and 3129 miss each a space before BytesPerWord. Change looks
fine otherwise.
Thanks, Thomas
Thanks,
>
> -Zhengyu
>
>
> All else looks fine to me now. I do not need another review.
>>
>> Thanks for your work, this will come in handy!
>>
>> ..Thomas
>>
>> On Tue, Oct 24, 2017 at 5:08 PM, Zhengyu Gu <zgu at redhat.com <mailto:
>> zgu at redhat.com>> wrote:
>>
>> Hi Thomas,
>>
>>
>> Not sure whether we misunderstood each other. I was thinking of
>> something in the line of:
>>
>> <<<<
>> ....
>> ClassLoader: jdk/internal/reflect/DelegatingClassLoader
>> Metadata:
>> capacity: 5.00KB used: 3.32KB free: 1.68KB
>> waste: 0.00KB
>> Class data:
>> capacity: 1.00KB used: 0.54KB free: 0.46KB
>> waste: 0.00KB
>>
>> ClassLoader: for anonymous class
>> Metadata:
>> capacity: 1.00KB used: 1.00KB free: 0.00KB
>> waste: 0.00KB
>> Class data:
>> capacity: 1.00KB used: 0.64KB free: 0.36KB
>> waste: 0.00KB
>> ....
>>
>> Summary:
>> XX class loaders encountered, total capacity: xx, total waste: xx.
>>
>> Peak usage by class loader: xxxx
>> >>>>
>>
>> Added summary lines:
>>
>> Total class loaders= 56 capacity= 6378.00KB used=
>> 6205.08KB free= 172.92KB waste= 1.44KB
>> For anonymous classes= 54 capacity= 212.00KB used= 96.95KB
>> free= 115.05KB waste= 0.94KB
>>
>>
>>
>>
>> These numbers would not be interpretation, just a convenience to
>> the reader to get a clear picture.
>>
>> It even may be useful to separate the output between basic and
>> detailed mode, and in basic mode omit all the single class
>> loaders and just print the summary line.
>>
>> Updated webrev:
>> http://cr.openjdk.java.net/~zgu/8189688/webrev.01/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.01/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.01/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.01/index.html>>
>>
>>
>>
>> metaspace.hpp:
>>
>> I would have preferred to keep scale_unit file local static
>> instead of exposing it via MetaspaceAux, because it does not
>> really have anything to do with metaspace.
>>
>> Fixed
>>
>>
>> Otherwise ok.
>>
>> ---
>>
>> metaspace.cpp
>>
>> - ChunkManager::print_statistics(): thanks for reusing this
>> function!
>> -> Scale can only be ever 1, K, M, G, yes? So, could you
>> add an assert at the start of the function, and a comment at the
>> prototype or function head?
>> -> Also, now that ChunkManager::print_statistics() takes a
>> scale, could you please change the printout to use floats like
>> you did in PrintCLDMetaspaceInfoClosure::print_metaspace()?
>>
>> Done.
>>
>>
>> Chunkmanager (non-class):
>> 0 specialized (128 bytes) chunks, total 0.00KB
>> 0 small (512 bytes) chunks, total 0.00KB
>> 0 medium (8192 bytes) chunks, total 0.00KB
>> 0 humongous chunks, total 0.00KB
>> total size: 0.00KB.
>> Chunkmanager (class):
>> 0 specialized (128 bytes) chunks, total 0.00KB
>> 0 small (256 bytes) chunks, total 0.00KB
>> 0 medium (4096 bytes) chunks, total 0.00KB
>> 0 humongous chunks, total 0.00KB
>> total size: 0.00KB.
>>
>>
>> - I am concerned about races in
>> PrintCLDMetaspaceInfoClosure::do_cld(ClassLoaderData* cld).
>> Maybe my understanding is limited. We bail if cld->is_unloading.
>> But nothing prevents a ClassLoaderDataGraph from starting to
>> unload a ClassLoaderData and tearing down the Metaspace after we
>> started printing it in another thread, right? Also, I do not see
>> any fences.
>>
>> So, I wonder whether PrintCLDMetaspaceInfoClosure should run in
>> lock protection. And then, I wonder if it would be good to
>> separate data gathering and printing. We print to a (at least in
>> principle) unknown output stream, which may be doing slow File
>> IO or even Network IO. Doing this under lock protection seems
>> not a good idea (but I see other places where this happens too).
>>
>> For an example, see ChunkManager::get_statistic() vs
>> ChunkManager::print_statistic(). Could you do the same, have a
>> data gathering step where you collect your
>> <capacity/used/free/waste> quadrupel in a variable sized list of
>> structures in memory, and print it out in a separate step? I
>> realize though that the effort would be larger than for what we
>> did in ChunkManager::get_statistic(), where we only fill a
>> structure.
>>
>>
>> Unlike other NMT queries, this query is executed at a safepoint by
>> VMThread, so it should be okay.
>>
>> Updated webrev: http://cr.openjdk.java.net/~zgu/8189688/webrev.02/
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.02/>
>>
>> Thanks,
>>
>> -Zhengyu
>>
>>
>> ------
>>
>> vm_operations.hpp
>>
>> - VM_PrintMetadata : do we still need _unit?
>>
>>
>> Thanks,
>>
>> -Zhengyu
>>
>>
>>
>> Thanks!
>>
>> Thomas
>>
>>
>>
>> On 10/23/2017 11:08 AM, Thomas Stüfe wrote:
>>
>>
>>
>> On Mon, Oct 23, 2017 at 5:03 PM, Zhengyu Gu
>> <zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>>> wrote:
>>
>>
>>
>> Okay. So this is important for understanding
>> cases
>> where we have
>> a large number of miniscule class loaders,
>> each one
>> only having
>> a few numbers of chunks. In this case, would it
>> be
>> useful to
>> have a running total of "free" and "waste",
>> too? Or
>> even better,
>> also average and peak values of "free" and
>> "waste" (to tell
>> apart cases where you have one outlier vs
>> cases where
>> just all
>> metaspaces waste a lot of memory).
>> Just out of curiosity, I looked at
>> http://cr.openjdk.java.net/~zgu/cld_metaspace/wildfly.txt
>> <http://cr.openjdk.java.net/~zgu/cld_metaspace/wildfly.txt>
>> <http://cr.openjdk.java.net/~z
>> gu/cld_metaspace/wildfly.txt
>> <http://cr.openjdk.java.net/~zgu/cld_metaspace/wildfly.txt>>
>> <http://cr.openjdk.java.net/~z
>> gu/cld_metaspace/wildfly.txt
>> <http://cr.openjdk.java.net/~zgu/cld_metaspace/wildfly.txt>
>> <http://cr.openjdk.java.net/~z
>> gu/cld_metaspace/wildfly.txt
>> <http://cr.openjdk.java.net/~zgu/cld_metaspace/wildfly.txt>>>
>> and
>> it seems that "free" is the problem, not
>> "waste"? So I
>> guess
>> what happens is that all the little classloaders
>> allocate just
>> enough memory to push them over
>> "_small_chunk_limit=4",
>> so they
>> allocate the first medium chunk, from which
>> then they
>> take a
>> small bite and leave the rest laying around?
>>
>> Yes. The free space of anonymous classes should be
>> counted
>> as waste,
>> in my opinion. I am not sure if everyone agrees,
>> so I took the
>> summary line out of this patch.
>>
>> I would be more than happy to restore the summary
>> line, if
>> you find
>> it is useful :-)
>>
>>
>> I agree with you. Typically class loaders stop loading
>> at some
>> point, especially these tine ones, and often will not
>> resume
>> loading. So, effectivly, the space is wasted. It still
>> helps to
>> distinguish "free" in the current chunks from "free" in
>> the
>> other chunks to tell this situation apart from a
>> situation where
>> we have just a bug in metaspace chunk handling
>> preventing us to
>> use up our chunks.
>>
>>
>> The latter would be an important
>> addition,
>> regardless
>> if this is
>> for customers or for us. Chunks idling
>> in
>> freelists can
>> make a
>> huge impact, and unfortunately this
>> may happen
>> in perfectly
>> valid cases. See e.g. our JEP
>> "
>> https://bugs.openjdk.java.net/browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>
>> <https://bugs.openjdk.java.net/browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>>
>> <https://bugs.openjdk.java.net
>> /browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>
>> <https://bugs.openjdk.java.net/browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>>>
>> <
>> https://bugs.openjdk.java.net/browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>
>> <https://bugs.openjdk.java.net/browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>>
>> <https://bugs.openjdk.java.net
>> /browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>
>> <https://bugs.openjdk.java.net/browse/JDK-8166690
>> <https://bugs.openjdk.java.net/browse/JDK-8166690>>>>". We have
>> already a printing routine for free
>> chunks, in
>> ChunkManager::print_all_chunkmanagers().
>> Could
>> you add
>> this to
>> your output?
>>
>>
>> Make sense! Could you recommend what data
>> and
>> format you
>> would like
>> to see?
>>
>>
>>
>> Would not
>> ChunkManager::print_all_chunkmanagers() be
>> sufficient?
>>
>> Okay, I might need to tweak output format.
>>
>>
>> Fine by me. Nothing depends on it yet.
>>
>> Thanks, Thomas
>>
>> Thanks,
>>
>> -Zhengyu
>>
>>
>>
>> -------------
>>
>> Other than above notes, the changes
>> seem
>> straighforward, I did
>> not see anything wrong. Minor nits:
>>
>> - PrintCLDMetaspaceInfoClosure::_out,
>> _scale
>> and _unit
>> could all
>> be constant (with _out being a
>> outputStream*
>> const).
>> - We also do not need to provide
>> scale *and*
>> unit as
>> argument,
>> one can be deduced from the other.
>> This would
>> also prevent
>> mismatches.We do need scale here,
>> since nmt
>> command
>> line can set
>> scale and we do
>>
>> have to honor that.
>>
>> However, passing unit is ugly! I don't
>> want to
>> introduce
>> inverse
>> dependence (metaspace -> nmt), which is
>> also ugly.
>>
>>
>> Yes, that would be regrettable.
>>
>> Probably should move scale mapping code
>> from
>> NMTUtil to a
>> common util?
>>
>>
>>
>> That would be possible, these functions
>> (scale_from_name etc)
>> are simple enough to be moved to a generic file.
>> However, if you
>> pass scale, deducing the string that goes with
>> it is
>> trivial and
>> I would have no qualms doing this by hand in
>> metaspace.cpp. But
>> it is a matter of taste.
>>
>>
>> I did not look closely at locking
>> issues, I assume
>> MetaspaceAux::print_metadata() is
>> supposed to
>> run only in
>> Safepoints?
>>
>>
>> No. sum_xxx_xxx_in_use queries are
>> guarded by locks.
>>
>> Thanks,
>>
>> -Zhengyu
>>
>>
>> Thanks, Thomas
>>
>>
>>
>> Thanks & Kind Regards, Thomas
>>
>>
>>
>>
>>
>>
>> On Fri, Oct 20, 2017 at 4:00 PM,
>> Zhengyu Gu
>> <zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>>
>> <mailto:zgu at redhat.com
>> <mailto:zgu at redhat.com> <mailto:zgu at redhat.com
>> <mailto:zgu at redhat.com>>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>>>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>>
>>
>> <mailto:zgu at redhat.com
>> <mailto:zgu at redhat.com> <mailto:zgu at redhat.com
>> <mailto:zgu at redhat.com>>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>> <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>>>>> wrote:
>>
>> Up to now, there is little
>> visibility
>> into how
>> metaspaces
>> are used,
>> and by whom.
>>
>> This proposed enhancement gives
>> NMT the
>> ability to
>> report
>> metaspace
>> usages on per-classloader level,
>> via a
>> new NMT command
>> "metadata"
>>
>>
>> For example:
>>
>> 2496:
>> Metaspaces:
>> Metadata space: reserved=
>> 8192KB
>> committed= 5888KB
>> Class space: reserved=
>> 1048576KB
>> committed= 640KB
>>
>> Per-classloader metadata:
>>
>> ClassLoader: for anonymous class
>> Metadata capacity=
>> 5.00KB
>> used= 1.16KB
>> free= 3.84KB waste= 0.05KB
>> Class data capacity=
>> 1.00KB
>> used= 0.59KB
>> free= 0.41KB waste= 0.00KB
>>
>> ....
>>
>> ClassLoader: <bootloader>
>> Metadata capacity=
>> 5640.00KB
>> used= 5607.42KB
>> free= 32.58KB waste=
>> 0.46KB
>> Class data capacity=
>> 520.00KB
>> used= 500.94KB
>> free= 19.06KB waste=
>> 0.02KB
>>
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>
>> <https://bugs.openjdk.java.net
>> /browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>>
>> <
>> https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>
>> <https://bugs.openjdk.java.net
>> /browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>>>
>> <
>> https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>
>> <https://bugs.openjdk.java.net
>> /browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>>
>> <
>> https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>
>> <https://bugs.openjdk.java.net
>> /browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>
>> <https://bugs.openjdk.java.net/browse/JDK-8189688
>> <https://bugs.openjdk.java.net/browse/JDK-8189688>>>>>
>> Webrev:
>> http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>>
>> <
>> http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>>>
>> <
>> http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>>
>> <
>> http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html>
>> <http://cr.openjdk.java.net/~z
>> gu/8189688/webrev.00/index.html
>> <http://cr.openjdk.java.net/~zgu/8189688/webrev.00/index.html
>> >>>>>
>>
>> Test:
>>
>> hotspot_tier1_runtime,
>> fastdebug and
>> release on
>> x64 Linux.
>>
>> Thanks,
>>
>> -Zhengyu
>>
>>
>>
>>
>>
>>
>>
>>
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