RFR(L): 8215624: add parallel heap inspection support for jmap histo(G1)(Internet mail)
linzang(臧琳)
linzang at tencent.com
Sun Apr 26 03:10:02 UTC 2020
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/
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?
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? 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!
BRs,
Lin
On 2020/4/23, 11:08 AM, "linzang(臧琳)" <linzang at tencent.com> 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" <hohensee at amazon.com> 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)" <serviceability-dev-bounces at openjdk.java.net on behalf of linzang at tencent.com> 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" <stefan.karlsson at oracle.com> 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)" <linzang at tencent.com> 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)" <linzang at tencent.com> 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)" <linzang at tencent.com> 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
>> > > >> >
>> > > >
>
>
>
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