Adding help information to log tags

[Rachel Protacio]

That seems like a good idea to me! It'd be helpful for the user and also 
anyone looking at the actual code in logTag.hpp
Rachel

On 12/23/2015 12:19 AM, Ioi Lam wrote:
> Now there are a lot of log tags [1], and it looks like many more will 
> be added. I start to wonder what 'ihop' or 'rt' would do ...
>
> Would it make sense to add help information that can be printed to the 
> user, like
>
> #define LOG_TAG_LIST \
>   LOG_TAG(alloc,      "this prints something about alloc") \
>   LOG_TAG(age,        "blah blah") \
>
> $ java -Xlog:help=alloc
> alloc - this prints something about alloc
>
> $ java -Xlog:help=all
> alloc - this prints something about alloc
> age   - blah blah
>
>
> -----------------
>
> [1] The list of log tags as of today in jdk9/hs-rt/hotspot
>
> #define LOG_TAG_LIST \
>   LOG_TAG(alloc) \
>   LOG_TAG(age) \
>   LOG_TAG(barrier) \
>   LOG_TAG(bot) \
>   LOG_TAG(census) \
>   LOG_TAG(classhisto) \
>   LOG_TAG(classinit) \
>   LOG_TAG(comp) \
>   LOG_TAG(compaction) \
>   LOG_TAG(cpu) \
>   LOG_TAG(cset) \
>   LOG_TAG(defaultmethods) \
>   LOG_TAG(ergo) \
>   LOG_TAG(exceptions) \
>   LOG_TAG(exit) \
>   LOG_TAG(freelist) \
>   LOG_TAG(gc) \
>   LOG_TAG(heap) \
>   LOG_TAG(humongous) \
>   LOG_TAG(ihop) \
>   LOG_TAG(jni) \
>   LOG_TAG(liveness) \
>   LOG_TAG(logging) \
>   LOG_TAG(marking) \
>   LOG_TAG(metaspace) \
>   LOG_TAG(monitorinflation) \
>   LOG_TAG(phases) \
>   LOG_TAG(plab) \
>   LOG_TAG(promotion) \
>   LOG_TAG(ref) \
>   LOG_TAG(refine) \
>   LOG_TAG(region) \
>   LOG_TAG(remset) \
>   LOG_TAG(rt) \
>   LOG_TAG(safepoint) \
>   LOG_TAG(scavenge) \
>   LOG_TAG(scrub) \
>   LOG_TAG(start) \
>   LOG_TAG(state) \
>   LOG_TAG(stats) \
>   LOG_TAG(stringdedup) \
>   LOG_TAG(survivor) \
>   LOG_TAG(svc) \
>   LOG_TAG(sweep) \
>   LOG_TAG(task) \
>   LOG_TAG(tlab) \
>   LOG_TAG(time) \
>   LOG_TAG(verify) \
>   LOG_TAG(vmoperation)
>
>