Request for review: 6521376: MaxTenuringThreshold and AlwayTenure/NeverTenure consistency

[Tao Mao]

Typos corrected.

Thanks.
Tao

On 6/22/13 8:03 PM, Tao Mao wrote:
> 6521376: MaxTenuringThreshold and AlwayTenure/NeverTenure consistency
>
> webrev:
> http://cr.openjdk.java.net/~tamao/6521376/webrev.00/
>
> changeset: For all collectors,
>
> (1) Setting -XX:+NeverTenure/-XX:+AlwaysTenure
> "-XX:+NeverTenure"
> ->
> NeverTenure=true; AlwaysTenure=false;  
> MaxTenuringThreshold=markOopDesc::max_age+1 (i.e. 16, use the value 
> instead below);
>
> "-XX:+AlwaysTenure"
> ->
> NeverTenure=false; AlwaysTenure=true;  MaxTenuringThreshold=0;
>
> (2) Setting MaxTenuringThreshold
>
> (2-a) MaxTenuringThreshold == 0
> if (MaxTenuringThreshold == 0):
> "the cap equals 0" implies AlwaysTenure=true, so set flags accordingly 
> (NeverTenure=false; AlwaysTenure=true).
>
> (2-b) MaxTenuringThreshold > 0
> But, considering the ergonomics for tenuring threshold (see 
> PSAdaptiveSizePolicy::compute_survivor_space_size_and_threshold(), 
> CMSAdaptiveSizePolicy::compute_survivor_space_size_and_threshold() and 
> ageTable::compute_tenuring_threshold()), we will adjust 
> tenure_threshold up and down but below the cap MaxTenuringThreshold 
> during the application run.
>
> Thus, setting MaxTenuringThreshold >= 16 would not necessarily imply 
> that the user wants to apply NeverTenure to the VM for the real 
> tenure_threshold may need to go below MaxTenuringThreshold as the 
> process stats suggest.
>
> With that said,
> if (MaxTenuringThreshold > 0):
> I simply set NeverTenure/AlwaysTenure to false. (neither NeverTenure 
> nor NeverTenure)
"I simply set both NeverTenure/AlwaysTenure to false. (neither 
NeverTenure nor AlwaysTenure)"
> and if (MaxTenuringThreshold > 16): set MaxTenuringThreshold to 16 as 
> it is unnecessary to be larger.
>
> *(3) -XX:-NeverTenure/-XX:-AlwaysTenure only need to take care of 
> themselves and don't need the flag consistency maintenance here.
>
> ******************************************************************************* 
>
> Take a little convoluted case for example: suppose that we have the 
> following gc options "-XX:+NeverTenure -XX:+MaxTenuringThreshold=18" 
> in this particular order.
>
> When we first parse "-XX:+NeverTenure", we would set: 
> NeverTenure=true; AlwaysTenure=false;  MaxTenuringThreshold=16.
>
> But when we encounter the second option 
> "-XX:+MaxTenuringThreshold=18", we would think the user knows about gc 
> ergonomics for tenuring threshold and wants MaxTenuringThreshold to 
> just be a cap for the ergonomics rather than wants to (implicitly) use 
> NeverTenure. So, we would set NeverTenure=false; AlwaysTenure=false; 
> and finally MaxTenuringThreshold=16 to reflect the cap maximum.
> ******************************************************************************* 
>
>
>