RFR: 6657: Add allocation pressure column to Memory and TLAB views

[Erik Gahlin]

On Thu, 19 Dec 2019 14:54:33 GMT, Erik Gahlin <egahlin at openjdk.org> wrote:

>> Hi Jie,
>> 
>> Thank you for looking at this! Here's some feedback before reviewing the code:
>> 
>> Memory tab:
>> 1. "Total Allocation Percentage" is a bit long. Can this be shortened? The description will be there is someone hovers over the header, for someone wanting more info. Maybe "Total Allocation (%)"?
>> 2. Should there perhaps be a backdrop bar in that column, for the percentage?
>> 
>> TLAB allocations:
>> 1. Same here, perhaps shorten the column width by having "Total Allocation (%)".
>> 2. Backdrop bar in that column too?
>> 3. Instead of spelling out Average, perhaps go with Avg? Instead of Allocation go with Alloc? Normally I'm against these kinds of shorthands, but this is a specialized tab, and some of these columns get really wide since the titles are so long. Much wider than their content, leading to waste of screen estate.
> 
> I think JMC 5.5 had good pick of default columns and names.
> https://www.javacodegeeks.com/wp-content/uploads/2015/03/jfr-allocations.png

I think we can skip any mention TLAB, at least if the purpose of the view is to find where the top allocation sites are.

I think Class | Sample Count | Pressure will be sufficiernt for 99% of all users.

There could be a seperate tab for those that want to tune TLABs, or hidden columns that can be made visisble for advanced users. In the future, we will probably add an ObjectAllocation event that can be on by default that will not leak implementation details as the TLABs.

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PR: https://git.openjdk.java.net/jmc/pull/21