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

[Erik Gahlin]

On Thu, 19 Dec 2019 14:43:30 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> This patch addresses https://bugs.openjdk.java.net/browse/JMC-6657, which itself is a clone of https://bugs.openjdk.java.net/browse/JMC-5923 that targets the Memory and TLAB pages, rather than the stacktrace view.
>> 
>> The ItemHistogram and related classes now have support for Percentage columns that divides the aggregate value for items in a row against the aggregate value for all items in the model.
>> 
>> This is used in the Memory page to show Total Allocation as a Percentage. The TLAB page is modified to be tabbed and contains two ItemHistograms, one for classifying against Threads (previously existed) and one against Top Methods (new). Both also have two new columns: allocations inside and outside TLABs, as a percentage.
>> 
>> ![tlab-page](https://user-images.githubusercontent.com/5430520/71093691-b2094c00-2177-11ea-9965-f27948964cd3.png)
>> TLABs by Top Methods, showcasing sorting by the new percentage column. Together with the stacktrace view, I believe these changes make it easier to see relevant areas of allocation pressure.
> 
> 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

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