RFR: 8204210: Implementation: JEP 333: ZGC: A Scalable Low-Latency Garbage Collector (Experimental)
Per Liden
per.liden at oracle.com
Wed Jun 6 19:44:35 UTC 2018
Hi Rickard,
Thanks a lot for reviewing, much appreciated! Comments below.
On 06/06/2018 11:48 AM, Rickard Bäckman wrote:
> Hi,
>
> I've looked at the C2 parts of things with Nils by my side.
> There are a couple of small things to note.
>
> classes.cpp misses an undef for optionalmacro.
Will fix.
>
> compile.cpp the print_method should probably be within the {} of
> macroExpand.
Will fix.
>
> escape.cpp has two else if cases where the code looks very common.
> Please make this into a function if possible?
It would be possible, but I'm not sure it's a great idea in this case.
The reason is that this seems to be the style in which these
switch-statements are written here. Just looking at the case statements
immediately above and below, they follow the same (duplication) pattern.
In the first switch is looks like this:
[...]
case Op_Proj: {
// we are only interested in the oop result projection from a call
if (n->as_Proj()->_con == TypeFunc::Parms && n->in(0)->is_Call() &&
n->in(0)->as_Call()->returns_pointer()) {
add_local_var_and_edge(n, PointsToNode::NoEscape,
n->in(0), delayed_worklist);
}
#if INCLUDE_ZGC
else if (UseZGC) {
if (n->as_Proj()->_con == LoadBarrierNode::Oop &&
n->in(0)->is_LoadBarrier()) {
add_local_var_and_edge(n, PointsToNode::NoEscape,
n->in(0)->in(LoadBarrierNode::Oop), delayed_worklist);
}
}
#endif
break;
}
case Op_Rethrow: // Exception object escapes
case Op_Return: {
if (n->req() > TypeFunc::Parms &&
igvn->type(n->in(TypeFunc::Parms))->isa_oopptr()) {
// Treat Return value as LocalVar with GlobalEscape escape state.
add_local_var_and_edge(n, PointsToNode::GlobalEscape,
n->in(TypeFunc::Parms), delayed_worklist);
}
break;
}
[...]
And in the second switch it looks like this:
[...]
case Op_Proj: {
// we are only interested in the oop result projection from a call
if (n->as_Proj()->_con == TypeFunc::Parms && n->in(0)->is_Call() &&
n->in(0)->as_Call()->returns_pointer()) {
add_local_var_and_edge(n, PointsToNode::NoEscape, n->in(0), NULL);
break;
}
#if INCLUDE_ZGC
else if (UseZGC) {
if (n->as_Proj()->_con == LoadBarrierNode::Oop &&
n->in(0)->is_LoadBarrier()) {
add_local_var_and_edge(n, PointsToNode::NoEscape,
n->in(0)->in(LoadBarrierNode::Oop), NULL);
break;
}
}
#endif
ELSE_FAIL("Op_Proj");
}
case Op_Rethrow: // Exception object escapes
case Op_Return: {
if (n->req() > TypeFunc::Parms &&
_igvn->type(n->in(TypeFunc::Parms))->isa_oopptr()) {
// Treat Return value as LocalVar with GlobalEscape escape state.
add_local_var_and_edge(n, PointsToNode::GlobalEscape,
n->in(TypeFunc::Parms), NULL);
break;
}
ELSE_FAIL("Op_Return");
}
[...]
So it would maybe look a bit odd if we use a different style for the
code we add, wouldn't you agree?
Also, since our code is in #if INCLUDE_ZGC blocks, breaking this out
would mean we would have to add a few more #if INCLUDE_ZGC blocks in
hpp/cpp to protect the new function. So, unless you strongly object, I'd
like to suggest that we keep it as is.
>
> opcodes.cpp misses an undef for optionalmacro.
Will fix.
>
> In C2 in general, maybe BarrierSet::barrier_set()->barrier_set_c2()
> coule be Compile::barrier_set()?
I agree that these names are a bit long, but may I suggest that we don't
do this as part of the ZGC patch? The reason is that there are already
21 pre-existing calls to BarrierSet::barrier_set()->barrier_set_c2() in
src/hotspot/share/opto code (we're adding 4 more in our patch). There
are another ~70 calls to the
BarrierSet::barrier_set()->barrier_set_{c1,assembler}() functions
throughout compiler/asm-related code. While shortening these names might
be a good idea, I'd prefer if that was handled separately from the ZGC
patch. Makes sense?
>
> Looks good, great work everyone!
Thanks! And again, thanks for reviewing!
/Per
>
> /R
>
> On 06/01, Per Liden wrote:
>> Hi,
>>
>> Please review the implementation of JEP 333: ZGC: A Scalable Low-Latency
>> Garbage Collector (Experimental)
>>
>> Please see the JEP for more information about the project. The JEP is
>> currently in state "Proposed to Target" for JDK 11.
>>
>> https://bugs.openjdk.java.net/browse/JDK-8197831
>>
>> Additional information in can also be found on the ZGC project wiki.
>>
>> https://wiki.openjdk.java.net/display/zgc/Main
>>
>>
>> Webrevs
>> -------
>>
>> To make this easier to review, we've divided the change into two webrevs.
>>
>> * ZGC Master: http://cr.openjdk.java.net/~pliden/8204210/webrev.0-master
>>
>> This patch contains the actual ZGC implementation, the new unit tests and
>> other changes needed in HotSpot.
>>
>> * ZGC Testing: http://cr.openjdk.java.net/~pliden/8204210/webrev.0-testing
>>
>> This patch contains changes to existing tests needed by ZGC.
>>
>>
>> Overview of Changes
>> -------------------
>>
>> Below follows a list of the files we add/modify in the master patch, with a
>> short summary describing each group.
>>
>> * Build support - Making ZGC an optional feature.
>>
>> make/autoconf/hotspot.m4
>> make/hotspot/lib/JvmFeatures.gmk
>> src/hotspot/share/utilities/macros.hpp
>>
>> * C2 AD file - Additions needed to generate ZGC load barriers (adlc does not
>> currently offer a way to easily break this out).
>>
>> src/hotspot/cpu/x86/x86.ad
>> src/hotspot/cpu/x86/x86_64.ad
>>
>> * C2 - Things that can't be easily abstracted out into ZGC specific code,
>> most of which is guarded behind a #if INCLUDE_ZGC and/or if (UseZGC)
>> condition. There should only be two logic changes (one in idealKit.cpp and
>> one in node.cpp) that are still active when ZGC is disabled. We believe
>> these are low risk changes and should not introduce any real change i
>> behavior when using other GCs.
>>
>> src/hotspot/share/adlc/formssel.cpp
>> src/hotspot/share/opto/*
>> src/hotspot/share/compiler/compilerDirectives.hpp
>>
>> * General GC+Runtime - Registering ZGC as a collector.
>>
>> src/hotspot/share/gc/shared/*
>> src/hotspot/share/runtime/vmStructs.cpp
>> src/hotspot/share/runtime/vm_operations.hpp
>> src/hotspot/share/prims/whitebox.cpp
>>
>> * GC thread local data - Increasing the size of data area by 32 bytes.
>>
>> src/hotspot/share/gc/shared/gcThreadLocalData.hpp
>>
>> * ZGC - The collector itself.
>>
>> src/hotspot/share/gc/z/*
>> src/hotspot/cpu/x86/gc/z/*
>> src/hotspot/os_cpu/linux_x86/gc/z/*
>> test/hotspot/gtest/gc/z/*
>>
>> * JFR - Adding new event types.
>>
>> src/hotspot/share/jfr/*
>> src/jdk.jfr/share/conf/jfr/*
>>
>> * Logging - Adding new log tags.
>>
>> src/hotspot/share/logging/*
>>
>> * Metaspace - Adding a friend declaration.
>>
>> src/hotspot/share/memory/metaspace.hpp
>>
>> * InstanceRefKlass - Adjustments for concurrent reference processing.
>>
>> src/hotspot/share/oops/instanceRefKlass.inline.hpp
>>
>> * vmSymbol - Disabled clone intrinsic for ZGC.
>>
>> src/hotspot/share/classfile/vmSymbols.cpp
>>
>> * Oop Verification - In four cases we disabled oop verification because it
>> do not makes sense or is not applicable to a GC using load barriers.
>>
>> src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp
>> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp
>> src/hotspot/share/compiler/oopMap.cpp
>> src/hotspot/share/runtime/jniHandles.cpp
>>
>> * StackValue - Apply a load barrier in case of OSR. This is a bit of a hack.
>> However, this will go away in the future, when we have the next iteration of
>> C2's load barriers in place (aka "C2 late barrier insertion").
>>
>> src/hotspot/share/runtime/stackValue.cpp
>>
>> * JVMTI - Adding an assert() to catch problems if the tagmap hashing is
>> changed in the future.
>>
>> src/hotspot/share/prims/jvmtiTagMap.cpp
>>
>> * Legal - Adding copyright/license for 3rd party hash function used in
>> ZHash.
>>
>> src/java.base/share/legal/c-libutl.md
>>
>> * SA - Adding basic ZGC support.
>>
>> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/*
>>
>>
>> Testing
>> -------
>>
>> * Unit testing
>>
>> A number of new ZGC specific gtests have been added, in
>> test/hotspot/gtest/gc/z/
>>
>> * Regression testing
>>
>> No new failures in Mach5, with ZGC enabled, tier{1,2,3,4,5,6}
>> No new failures in Mach5, with ZGC disabled, tier{1,2,3}
>>
>> * Stress testing
>>
>> We have been continuously been running a number stress tests throughout
>> the development, these include:
>>
>> specjbb2000
>> specjbb2005
>> specjbb2015
>> specjvm98
>> specjvm2008
>> dacapo2009
>> test/hotspot/jtreg/gc/stress/gcold
>> test/hotspot/jtreg/gc/stress/systemgc
>> test/hotspot/jtreg/gc/stress/gclocker
>> test/hotspot/jtreg/gc/stress/gcbasher
>> test/hotspot/jtreg/gc/stress/finalizer
>> Kitchensink
>>
>>
>> Thanks!
>>
>> /Per, Stefan & the ZGC team
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