On Fri, 23 Apr 2021 19:48:47 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. src/hotspot/share/classfile/vmSymbols.hpp line 490: > 488: template(data_cache_line_flush_size_name, > "DATA_CACHE_LINE_FLUSH_SIZE") \ > 489: template(during_unsafe_access_name, > "during_unsafe_access") \ > 490: template(no_deduplication_name, > "no_deduplication") \ This addition was left over from an earlier version of the change, where I'd added an ordinary private boolean member of this name to String. That was before I learned about injected members and before the idea of adding "duplication requested" came up. This name is no longer needed, and I'll be removing it. ------------- PR: https://git.openjdk.java.net/jdk/pull/3662