RFR: 8231489: GC watermark_0_1 failed due to "metaspace.gc.Fault: GC has happened too rare"

[Thomas Schatzl]

Hi,

On 03.10.19 10:47, Per Liden wrote:
> vmTestbase/metaspace/gc/HighWaterMarkTest relies on timing and fails 
> when "Metaspace GC Threshold" isn't handled in a STW pause.
> 
> The problem can be reproduced on both G1 and ZGC, but it's hard, as the 
> window is small. However, it reproduces every time when injecting a 
> 100ms delay to prolong the GC cycle a bit. This test used to be disabled 
> for G1 with ClassUnloadingWithConcurrentMark, but JDK-8204163 enabled it 
> about a year ago.
> 
> Fixing the test properly is tricky. As far as I can see, we can either:
> 1) Disable this test for G1+ClassUnloadingWithConcurrentMark and ZGC, or
> 2) Add a sleep in the test loop, to make the race less likely to happen, or
> 3) Remove the test completely, with the rational that it's a buggy low 
> value test.
> 
> I've gone with 1) here. The test is already disabled for CMS today, with 
> code in the test itself (i.e. not using @requires), so I did two 
> alternative patches:
> 
> A) Follows the existing style to disable the other GCs:
> http://cr.openjdk.java.net/~pliden/8231489/webrev.0-alt1
> 
> B) Adds @requires to the tests using the HighWaterMarkTest class, and 
> removes the old check to disable CMS:
> http://cr.openjdk.java.net/~pliden/8231489/webrev.0-alt2
> 
> I prefer B, but I don't have a strong opinion on which way to go.
> 

B is fine with me.

Looks good.

Thomas