Dear All,
May I ask your help again for review the latest change? Thanks!
BRs,
Lin
On 2020/4/28, 1:54 PM, "linzang(臧琳)" <[email protected]> wrote:
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
> >> > > >> >
> >> > > >
> >
> >
> >
>
>
>
>
>
>
