Hi Stefan,
>> - Adding Atomic::load/store.
>> - Removing the time measurement in the run_task. I renamed G1's function
>> to run_task_timed. If we need this outside of G1, we can rethink the API
>> at that point.
>> - ZGC style cleanups
Thanks for revising the patch, they are all good to me, and I have made a
tiny change based on it:
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_04/
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_04-delta/
it reduce the scope of mutex in ParHeapInspectTask, and delete unnecessary
comments.
BRs,
Lin
On 2020/4/27, 4:34 PM, "Stefan Karlsson" <[email protected]> wrote:
Hi Lin,
On 2020-04-26 05:10, linzang(臧琳) wrote:
> Hi Stefan and Paul，
> I have made a new patch based on your comments and Stefan's Poc code:
> Webrev:
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_03/
> Delta(based on Stefan's change:) :
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_03-delta/webrev_03-delta/
Thanks for providing a delta patch. It makes it much easier to look at,
and more likely for reviewers to continue reviewing.
I'm going to continue focusing on the GC parts, and leave the rest to
others to review.
>
> And Here are main changed I made and want to discuss with you:
> 1. changed"parallelThreadNum=" to "parallel=" for jmap -histo
options.
> 2. Add logic to test where parallelHeapInspection is fail, in
heapInspection.cpp
> This is because the parHeapInspectTask create thread local
KlassInfoTable in it's work() method, and this may fail because of native OOM,
in this case, the parallel should fail and serial heap inspection can be tried.
> One more thing I want discuss with you is about the member
"_success" of parHeapInspectTask, when native OOM happenes, it is set to false.
And since this "set" operation can be conducted in multiple threads, should it
be atomic ops? IMO, this is not necessary because "_success" can only be set
to false, and there is no way to change it from back to true after the
ParHeapInspectTask instance is created, so it is save to be non-atomic, do you
agree with that?
In these situations you should be using the Atomic::load/store
primitives. We're moving toward a later C++ standard were data races are
considered undefined behavior.
> 3. make CollectedHeap::run_task() be an abstract virtual func, so
that every subclass of collectedHeap should support it, so later implementation
of new collectedHeap will not miss the "parallel" features.
> The problem I want to discuss with you is about epsilonHeap and
SerialHeap, as they may not need parallel heap iteration, so I only make
task->work(0), in case the run_task() is invoked someway in future. Another way
is to left run_task() unimplemented, which one do you think is better?
I don't have a strong opinion about this.
And also please help take a look at the zHeap, as there is a class
zTask that wrap the abstractGangTask, and the collectedHeap::run_task()
only accept AbstraceGangTask* as argument, so I made a delegate class
to adapt it , please see src/hotspot/share/gc/z/zHeap.cpp.
>
> There maybe other better ways to sovle the above problems, welcome
for any comments, Thanks!
I've created a few cleanups and changes on top of your latest patch:
https://cr.openjdk.java.net/~stefank/8215624/webrev.02.delta
https://cr.openjdk.java.net/~stefank/8215624/webrev.02
- Adding Atomic::load/store.
- Removing the time measurement in the run_task. I renamed G1's function
to run_task_timed. If we need this outside of G1, we can rethink the API
at that point.
- ZGC style cleanups
Thanks,
StefanK
>
> BRs,
> Lin
>
> On 2020/4/23, 11:08 AM, "linzang(臧琳)" <[email protected]> wrote:
>
> Thanks Paul! I agree with using "parallel", will make the update in
next patch, Thanks for help update the CSR.
>
> BRs,
> Lin
>
> On 2020/4/23, 4:42 AM, "Hohensee, Paul" <[email protected]> wrote:
>
> For the interface, I'd use "parallel" instead of
"parallelThreadNum". All the other options are lower case, and it's a lot
easier to type "parallel". I took the liberty of updating the CSR. If you're ok
with it, you might want to change variable names and such, plus of course
JMap.usage.
>
> Thanks,
> Paul
>
> On 4/22/20, 2:29 AM, "serviceability-dev on behalf of
linzang(臧琳)" <[email protected] on behalf of
[email protected]> wrote:
>
> Dear Stefan,
>
> Thanks a lot! I agree with you to decouple the heap
inspection code with GC's.
> I will start from your POC code, may discuss with
you later.
>
>
> BRs,
> Lin
>
> On 2020/4/22, 5:14 PM, "Stefan Karlsson"
<[email protected]> wrote:
>
> Hi Lin,
>
> I took a look at this earlier and saw that the heap
inspection code is
> strongly coupled with the CollectedHeap and
G1CollectedHeap. I'd prefer
> if we'd abstract this away, so that the GCs only provide
a "parallel
> object iteration" interface, and the heap inspection
code is kept elsewhere.
>
> I started experimenting with doing that, but other
higher-priority (to
> me) tasks have had to take precedence.
>
> I've uploaded my work-in-progress / proof-of-concept:
>
https://cr.openjdk.java.net/~stefank/8215624/webrev.01.delta/
> https://cr.openjdk.java.net/~stefank/8215624/webrev.01/
>
> The current code doesn't handle the lifecycle (deletion)
of the
> ParallelObjectIterators. There's also code left
unimplemented in around
> CollectedHeap::run_task. However, I think this could
work as a basis to
> pull out the heap inspection code out of the GCs.
>
> Thanks,
> StefanK
>
> On 2020-04-22 02:21, linzang(臧琳) wrote:
> > Dear all,
> > May I ask you help to review? This RFR has been
there for quite a while.
> > Thanks!
> >
> > BRs,
> > Lin
> >
> > > On 2020/3/16, 5:18 PM, "linzang(臧琳)"
<[email protected]> wrote:>
> >
> >> Just update a new path, my preliminary measure
show about 3.5x speedup of jmap histo on a nearly full 4GB G1 heap (8-core
platform with parallel thread number set to 4).
> >> webrev:
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_02/
> >> bug:
https://bugs.openjdk.java.net/browse/JDK-8215624
> >> CSR:
https://bugs.openjdk.java.net/browse/JDK-8239290
> >> BRs,
> >> Lin
> >> > On 2020/3/2, 9:56 PM, "linzang(臧琳)"
<[email protected]> wrote:
> >> >
> >> > Dear all,
> >> > Let me try to ease the reviewing
work by some explanation :P
> >> > The patch's target is to speed up
jmap -histo for heap iteration, from my experience it is necessary for large
heap investigation. E.g in bigData scenario I have tried to conduct jmap -histo
against 180GB heap, it does take quite a while.
> >> > And if my understanding is corrent,
even the jmap -histo without "live" option does heap inspection with heap lock
acquired. so it is very likely to block mutator thread in allocation-sensitive
scenario. I would say the faster the heap inspection does, the shorter the
mutator be blocked. This is parallel iteration for jmap is necessary.
> >> > I think the parallel heap inspection
should be applied to all kind of heap. However, consider the heap layout are
different for GCs, much time is required to understand all kinds of the heap
layout to make the whole change. IMO, It is not wise to have a huge patch for
the whole solution at once, and it is even harder to review it. So I plan to
implement it incrementally, the first patch (this one) is going to confirm the
implemention detail of how jmap accept the new option, passes it to
attachListener of the jvm process and then how to make the parallel inspection
closure be generic enough to make it easy to extend to different heap layout.
And also how to implement the heap inspection in specific gc's heap. This patch
use G1's heap as the begining.
> >> > This patch actually do several
things:
> >> > 1. Add an option
"parallelThreadNum=<N>" to jmap -histo, the default behavior is to set N to 0,
means let's JVM decide how many threads to use for heap inspection. Set this
option to 1 will disable parallel heap inspection. (more details in CSR:
https://bugs.openjdk.java.net/browse/JDK-8239290)
> >> > 2. Make a change in how Jmap passing
arguments, changes in
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_01/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java.udiff.html,
originally it pass options as separate arguments to attachListener, this patch
change to that all options be compose to a single string. So the arg_count_max
in attachListener.hpp do not need to be changed, and hence avoid the
compatibility issue, as disscussed at
https://mail.openjdk.java.net/pipermail/serviceability-dev/2019-March/027334.html
> >> > 3. Add an abstract class
ParHeapInspectTask in heapInspection.hpp / heapInspection.cpp, It's work(uint
worker_id) method prepares the data structure (KlassInfoTable) need for every
parallel worker thread, and then call do_object_iterate_parallel() which is
heap specific implementation. I also added some machenism in KlassInfoTable to
support parallel iteration, such as merge().
> >> > 4. In specific heap (G1 in this
patch), create a subclass of ParHeapInspectTask, implement the
do_object_iterate_parallel() for parallel heap inspection. For G1, it simply
invoke g1CollectedHeap's object_iterate_parallel().
> >> > 5. Add related test.
> >> > 6. it may be easy to extend this patch
for other kinds of heap by creating subclass of ParHeapInspectTask and
implement the do_object_iterate_parallel().
> >> >
> >> > Hope these info could help on code review
and initate the discussion :-)
> >> > Thanks!
> >> >
> >> > BRs,
> >> > Lin
> >> > >On 2020/2/19, 9:40 AM, "linzang(臧琳)"
<[email protected]> wrote:.
> >> > >
> >> > > Re-post this RFR with correct
enhancement number to make it trackable.
> >> > > please ignore the previous wrong post.
sorry for troubles.
> >> > >
> >> > > webrev:
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215624/webrev_01/
> >> > > Hi bug:
https://bugs.openjdk.java.net/browse/JDK-8215624
> >> > > CSR:
https://bugs.openjdk.java.net/browse/JDK-8239290
> >> > > --------------
> >> > > Lin
> >> > > >Hi Lin,
> > > > > >
> >> > > >Could you, please, re-post your RFR
with the right enhancement number in
> >> > > >the message subject?
> >> > > >It will be more trackable this way.
> >> > > >
> >> > > >Thanks,
> >> > > >Serguei
> >> > > >
> >> > > >
> >> > > >On 2/17/20 10:29 PM, linzang(臧琳)
wrote:
> >> > > >> Dear David,
> >> > > >> Thanks a lot!
> >> > > >> I have updated the refined
code to http://cr.openjdk.java.net/~lzang/jmap-8214535/8215264/webrev_01/.
> >> > > >> IMHO the parallel heap
inspection can be extended to all kinds of heap as long as the heap layout can
support parallel iteration.
> >> > > >> Maybe we can firstly use
this webrev to discuss how to implement it, because I am not sure my current
implementation is an appropriate way to communicate with collectedHeap, then we
can extend the solution to other kinds of heap.
> >> > > >>
> >> > > >> Thanks,
> >> > > >> --------------
> >> > > >> Lin
> >> > > >>> Hi Lin,
> >> > > >>>
> >> > > >>> Adding in hotspot-gc-dev as they
need to see how this interacts with GC
> >> > > >>> worker threads, and whether it
needs to be extended beyond G1.
> >> > > >>>
> >> > > >>> I happened to spot one nit when
browsing:
> >> > > >>>
> >> > > >>>
src/hotspot/share/gc/shared/collectedHeap.hpp
> >> > > >>>
> >> > > >>> + virtual bool
run_par_heap_inspect_task(KlassInfoTable* cit,
> >> > > >>> +
BoolObjectClosure* filter,
> >> > > >>> +
size_t* missed_count,
> >> > > >>> +
size_t thread_num) {
> >> > > >>> + return NULL;
> >> > > >>>
> >> > > >>> s/NULL/false/
> >> > > >>>
> >> > > >>> Cheers,
> >> > > >>> David
> > > > > >>>
> >> > > >>> On 18/02/2020 2:15 pm,
linzang(臧琳) wrote:
> >> > > >>>> Dear All,
> >> > > >>>> May I ask your help to
review the follow changes:
> >> > > >>>> webrev:
> >> > > >>>>
http://cr.openjdk.java.net/~lzang/jmap-8214535/8215264/webrev_00/
> >> > > >>>> bug:
https://bugs.openjdk.java.net/browse/JDK-8215624
> >> > > >>>> related CSR:
https://bugs.openjdk.java.net/browse/JDK-8239290
> >> > > >>>> This patch enable
parallel heap inspection of G1 for jmap histo.
> >> > > >>>> my simple test shown it
can speed up 2x of jmap -histo with
> >> > > >>>> parallelThreadNum set to 2 for
heap at ~500M on 4-core platform.
> >> > > >>>>
> >> > > >>>>
------------------------------------------------------------------------
> >> > > >>>> BRs,
> >> > > >>>> Lin
> >> > > >> >
> >> > > >
> >
> >
> >
>
>
>
>
>
>
