On Fri, 14 May 2021 04:31:59 GMT, Kim Barrett <kbarr...@openjdk.org> wrote:
>> Please review this change to the String Deduplication facility. It is being
>> changed to use OopStorage to hold weak references to relevant objects,
>> rather than bespoke data structures requiring dedicated processing phases by
>> supporting GCs.
>>
>> (The Shenandoah update was contributed by Zhengyu Gu.)
>>
>> This change significantly simplifies the interface between a given GC and
>> the String Deduplication facility, which should make it much easier for
>> other GCs to opt in. However, this change does not alter the set of GCs
>> providing support; currently only G1 and Shenandoah support string
>> deduplication. Adding support by other GCs will be in followup RFEs.
>>
>> Reviewing via the diffs might not be all that useful for some parts, as
>> several files have been essentially completely replaced, and a number of
>> files have been added or eliminated. The full webrev might be a better
>> place to look.
>>
>> The major changes are in gc/shared/stringdedup/* and in the supporting
>> collectors, but there are also some smaller changes in other places, most
>> notably classfile/{stringTable,javaClasses}.
>>
>> This change is additionally labeled for review by core-libs, although there
>> are no source changes there. This change injects a byte field of bits into
>> java.lang.String, using one of the previously unused padding bytes in that
>> class. (There were two unused bytes, now only one.)
>>
>> Testing:
>> mach5 tier1-2 with and without -XX:+UseStringDeduplication
>>
>> Locally (linux-x64) ran all of the existing tests that use string
>> deduplication with both G1 and Shenandoah. Note that
>> TestStringDeduplicationInterned.java is disabled for shenandoah, as it
>> currently fails, for reasons I haven't figured out but suspect are test
>> related.
>>
>> - gc/stringdedup/ -- these used to be in gc/g1
>> - runtime/cds/SharedStringsDedup.java
>> - runtime/cds/appcds/cacheObject/DifferentHeapSizes.java
>> - runtime/cds/appcds/sharedStrings/*
>>
>> shenandoah-only:
>> - gc/shenandoah/jvmti/TestHeapDump.java
>> - gc/shenandoah/TestStringDedup.java
>> - gc/shenandoah/TestStringDedupStress.java
>>
>> Performance tested baseline, baseline + stringdedup, new with stringdedup,
>> finding no significant differences.
>
> Kim Barrett has updated the pull request with a new target base due to a
> merge or a rebase. The pull request now contains eight commits:
>
> - Merge branch 'master' into new_dedup2
> - misc cleanups
> - refactor Requests::add
> - fix typo
> - more comment improvements
> - improve naming and comments around injected String flags
> - fix some typos in comments
> - New string deduplication
> The "merge from master" commit
> ([ccb9951](https://github.com/openjdk/jdk/commit/ccb99515d020785d7fe1cf9a1c247aeed775dc19))
> doesn't build with Shenandoah. I've asked Zhengyu to take a look.
Just missing a parameter:
```diff --git a/src/hotspot/share/gc/shenandoah/shenandoahSTWMark.cpp
b/src/hotspot/share/gc/shenandoah/shenandoahSTWMark.cpp
index ddaa66ccc14..93a067fa22d 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahSTWMark.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahSTWMark.cpp
@@ -57,7 +57,7 @@
ShenandoahInitMarkRootsClosure::ShenandoahInitMarkRootsClosure(ShenandoahObjToSc
template <class T>
void ShenandoahInitMarkRootsClosure::do_oop_work(T* p) {
- ShenandoahMark::mark_through_ref<T, NO_DEDUP>(p, _queue, _mark_context,
false);
+ ShenandoahMark::mark_through_ref<T, NO_DEDUP>(p, _queue, _mark_context,
NULL, false);
}```
src/hotspot/share/gc/shared/stringdedup/stringDedupTable.cpp line 314:
> 312: size_t _bucket_index;
> 313: size_t _shrink_index;
> 314: bool _grow_only;
Indentation
-------------
PR: https://git.openjdk.java.net/jdk/pull/3662
