RFR(xs): 8152118: MinTLABSize should be less than TLAB max

[Bengt Rutisson]

Hi Sangheon,

On 2016-03-18 06:43, sangheon wrote:
> Hi all,
>
> Could I have a couple of reviews for this tiny change?
>
> MinTLABSize doesn't have upper limit now and this change is proposing 
> to be less than or equal to ThreadLocallAllocBuffer::max_size().
>
> CR: https://bugs.openjdk.java.net/browse/JDK-8152118
> Webrev: http://cr.openjdk.java.net/~sangheki/8152118/webrev.00/

I think this looks good.

However, I have a related question. When I set up the min tlab size high 
I get some issues reported from other constraint functions:

$ java  -XX:MinTLABSize=16m -XX:G1HeapRegionSize=32m -version
YoungPLABSize (4096) must be greater than or equal to ergonomic PLAB 
minimum size (2097152)
OldPLABSize (1024) must be greater than or equal to ergonomic PLAB 
minimum size (2097152)
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

I don't think this is a problem with the patch that you are proposing 
now, but I thought I should mention it. Do you think this is something 
we would like to fix in the argument parsing (like adjusting the PLAB 
max to be at least PLAB min) or should we just let the users set up the 
PLAB sizes if they use large TLAB sizes?

This is a pre-exiting problem. Even without your patch I get the same 
behavior. So, you can consider your proposed patched reviewed.

Thanks,
Bengt


> Testing: JPRT, TestOptionsWithRanges.java for all platforms.
>
> Thanks,
> Sangheon