> 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 incrementally with three additional commits since the last revision: - more comment improvements - improve naming and comments around injected String flags - fix some typos in comments ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/3662/files - new: https://git.openjdk.java.net/jdk/pull/3662/files/2df362cb..656e2426 Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3662&range=01 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3662&range=00-01 Stats: 70 lines in 8 files changed: 8 ins; 2 del; 60 mod Patch: https://git.openjdk.java.net/jdk/pull/3662.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/3662/head:pull/3662 PR: https://git.openjdk.java.net/jdk/pull/3662