RFR: 8232365: Implementation for JEP 363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector

[Leo Korinth]

On 18/10/2019 11:20, David Holmes wrote:
> Hi Leo,
> 
> Picking up on one item ...
> 
>  > Not fully addressed in code, but an issue that has to be dealt with, how
>  > do I obsolete -Xconcgc and -Xnoconcgc? I believe the option should be
>  > obsoleted, though I do not know if we have any precedence obsoleting -X
>  > options.
> 
> These flags (which are passed through from the launcher) are already 
> marked as deprecated. So to "obsolete" them you just need to update the 
> warning that gets issued (and otherwise delete them from the code). So 
> you need to change this code in arguments.cpp to produce the appropriate 
> obsoletion warning similar to what we issue for obsoleted -XX flags:
> 
>     // -Xconcgc
>      } else if (match_option(option, "-Xconcgc")) {
>        if (FLAG_SET_CMDLINE(UseConcMarkSweepGC, true) != 
> JVMFlag::SUCCESS) {
>          return JNI_EINVAL;
>        }
>        handle_extra_cms_flags("-Xconcgc uses UseConcMarkSweepGC");
>      // -Xnoconcgc
>      } else if (match_option(option, "-Xnoconcgc")) {
>        if (FLAG_SET_CMDLINE(UseConcMarkSweepGC, false) != 
> JVMFlag::SUCCESS) {
>          return JNI_EINVAL;
>        }
>        handle_extra_cms_flags("-Xnoconcgc uses UseConcMarkSweepGC");
> 
> Let me know if you need more details.
> 
> Then file a follow up issue to remove these flags in the future. I don't 
> know if you have a timeline for that yet.
> 
> Cheers,
> David
> -----


Hi David, I filed https://bugs.openjdk.java.net/browse/JDK-8232739

Do you suggest something like this?

diff --git a/src/hotspot/share/runtime/arguments.cpp 
b/src/hotspot/share/runtime/arguments.cpp
index 620168b4e4b..c0a9acea962 100644
--- a/src/hotspot/share/runtime/arguments.cpp
+++ b/src/hotspot/share/runtime/arguments.cpp
@@ -2615,10 +2615,10 @@ jint Arguments::parse_each_vm_init_arg(const 
JavaVMInitArgs* args, bool* patch_m
        }
      // -Xconcgc
      } else if (match_option(option, "-Xconcgc")) {
-      handle_extra_cms_flags("-Xconcgc uses UseConcMarkSweepGC");
+      warning("-Xconcgc uses UseConcMarkSweepGC; support was removed 
for both options in 14.0");
      // -Xnoconcgc
      } else if (match_option(option, "-Xnoconcgc")) {
-      handle_extra_cms_flags("-Xnoconcgc uses UseConcMarkSweepGC");
+      warning("-Xnoconcgc uses UseConcMarkSweepGC; support was removed 
for both options in 14.0");
      // -Xbatch
      } else if (match_option(option, "-Xbatch")) {
        if (FLAG_SET_CMDLINE(BackgroundCompilation, false) != 
JVMFlag::SUCCESS) {
@@ -3859,15 +3859,6 @@ bool Arguments::handle_deprecated_print_gc_flags() {
    return true;
  }

-void Arguments::handle_extra_cms_flags(const char* msg) {
-  SpecialFlag flag;
-  const char *flag_name = "UseConcMarkSweepGC";
-  if (lookup_special_flag(flag_name, flag)) {
-    handle_aliases_and_deprecation(flag_name, /* print warning */ true);
-    warning("%s", msg);
-  }
-}
-
  // Parse entry point called from JNI_CreateJavaVM

  jint Arguments::parse(const JavaVMInitArgs* initial_cmd_args) {
diff --git a/src/hotspot/share/runtime/arguments.hpp 
b/src/hotspot/share/runtime/arguments.hpp
index d9aa77af315..2759836bb88 100644
--- a/src/hotspot/share/runtime/arguments.hpp
+++ b/src/hotspot/share/runtime/arguments.hpp
@@ -425,8 +425,6 @@ class Arguments : AllStatic {

    static bool handle_deprecated_print_gc_flags();

-  static void handle_extra_cms_flags(const char* msg);
-
    static jint parse_vm_init_args(const JavaVMInitArgs 
*java_tool_options_args,
                                   const JavaVMInitArgs *java_options_args,
                                   const JavaVMInitArgs *cmd_line_args);


Thanks,
Leo

> 
> On 18/10/2019 6:20 pm, Leo Korinth wrote:
>> Hi,
>>
>> Here is a patch that removes the CMS GC.
>>
>> I have neither tested arm nor ppc; I hope my changes to those .ad 
>> files are correct, if someone can test those architectures, that would 
>> be great.
>>
>> Please take an extra look at 
>> CollectedHeap::check_for_non_bad_heap_word_value, it was buggy before 
>> (but never called), It is now called (and hopefully correct).
>>
>> I have tried to remove most parts of CMS. I have not made it a goal to 
>> remove all traces of CMS. I guess there are much more to cleanup, and 
>> suggestions of more to remove are welcomed. I think more complicated 
>> cleanups should be dealt with in separate enhancements.
>>
>> Not fully addressed in code, but an issue that has to be dealt with, 
>> how do I obsolete -Xconcgc and -Xnoconcgc? I believe the option should 
>> be obsoleted, though I do not know if we have any precedence 
>> obsoleting -X options.
>>
>> My patch prints:
>>
>> $ java -Xconcgc -jar Notepad.jar
>> Java HotSpot(TM) 64-Bit Server VM warning: -Xconcgc uses 
>> UseConcMarkSweepGC
>>
>> I guess that is not enough for being obsolete, compare with:
>>
>> $ java -XX:UseConcMarkSweepGC -jar Notepad.jar
>> Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option 
>> UseConcMarkSweepGC; support was removed in 14.0
>>
>> Bug:
>>    https://bugs.openjdk.java.net/browse/JDK-8232365
>>
>> Webrev:
>>    http://cr.openjdk.java.net/~lkorinth/8232365/00
>>
>> Testing:
>>    tier 1-5.
>>
>> Thanks,
>> Leo