I'd like to see this feature added. :)
The CSR looks good, as does the basic parallel inspection algorithm. Stefan's
done the GC part, so I'll stick to the non-GC part (fwiw, the GC part lgtm).
I'd move all the argument parsing code to JMap.java and just pass the results
to Hotspot. Both histo() in JMap.java and code in attachListener.* parse the
command line arguments, though the code in histo() doesn't parse the argument
to "parallel". I'd upgrade the code in histo() to do a complete parse and pass
the option values to executeCommandForPid as before: there would just be more
of them now. That would allow you to eliminate all the parsing code in
attachListener.cpp as well as the change to arguments.hpp.
heapInspection.hpp:
_shared_miss_count (s/b _missed_count, see below) isn't a size, so it should be
a uint instead of a size_t. Same with the new parallel_thread_num argument to
heap_inspection() and populate_table().
Comment copy-edit:
+// Parallel heap inspection task. Parallel inspection can fail due to
+// a native OOM when allocating memory for TL-KlassInfoTable.
+// _success will be set false on an OOM, and serial inspection tried.
_shared_miss_count should be _missed_count to match the missed_count() getter,
or rename missed_count() to be shared_miss_count(). Whichever way you go, the
field type should match the getter result type: uint is reasonable.
heapInspection.cpp:
You might use ResourceMark twice in populate_table, separately for the parallel
attempt and the serial code. If the parallel attempt fails and available memory
is low, it would be good to clean up the memory used by the parallel attempt
before doing the serial code.
Style nit in KlassInfoTable::merge_entry(). I'd line up the definitions of k
and elt, so "k" is even with "elt". And, because it's two lines shorter, I'd
replace
+ } else {
+ return false;
+ }
with
+ return false;
KlassInfoTableMergeClosure.is_success() should be just success() (i.e., no
"is_" prefix) because it's a getter.
I'd reorganize the code in populate_table() to make it more clear, vis (I
changed _shared_missed_count to _missed_count)
+ if (cit.allocation_failed()) {
+ // fail to allocate memory, stop parallel mode
+ Atomic::store(&_success, false);
+ return;
+ }
+ RecordInstanceClosure ric(&cit, _filter);
+ _poi->object_iterate(&ric, worker_id);
+ missed_count = ric.missed_count();
+ {
+ MutexLocker x(&_mutex);
+ merge_success = _shared_cit->merge(&cit);
+ }
+ if (merge_success) {
+ Atomic::add(&_missed_count, missed_count);
+ else {
+ Atomic::store(&_success, false);
+ }
Thanks,
Paul
On 6/29/20, 7:20 PM, "linzang(臧琳)" <[email protected]> wrote:
Dear All,
Sorry to bother again, I just want to make sure that is this change
worth to be continue to work on? If decision is made to not. I think I can drop
this work and stop asking for help reviewing...
Thanks for all your help about reviewing this previously.
BRs,
Lin
On 2020/5/9, 3:47 PM, "linzang(臧琳)" <[email protected]> wrote:
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
> >> > > >> >
> >> > > >
> >
> >
> >
>
>
>
>
>
>
