RFR(xs): 8152118: MinTLABSize should be less than TLAB max
bengt.rutisson at oracle.com
Mon Mar 21 10:00:07 UTC 2016
On 2016-03-18 18:28, sangheon wrote:
> Hi Bengt,
> Thanks for reviewing this.
> On 03/18/2016 12:15 AM, Bengt Rutisson wrote:
>> 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
>>> 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.
> Right, we have this problem when we introduced range/constraint for
> command-line flags (JDK-8059557: JEP 245: Validate JVM Command-Line
> Flag Arguments).
> And adjusting the flag during argument processing was out-of-scope.
> (Non-goal: second item)
Thanks for this background information. But just because it was out of
scope for JEP 245 doesn't mean that we can't fix it now if we want,
> Your opinion seems like adjusting related flags, am I correct? i.e. We
> set 'MinTLABSize' but the error happened related flags(YoungPLABSize
> and OldPLABSize). And then, I think it would be better to let the
> users set-up them because it will be hard to adjusting related flags.
> What extends we would decide candidate flags to adjust.
> But I agree with you that it would be annoying for the users.
Yes, argument consistency is really difficult to get completely right.
You can spend a lot of time on it and still miss some border cases. I
just thought that in this case it looked simple enough. We should
probably not select PLAB sizes that smaller than the min PLAB size.
But I haven't looked at the code. Just the error messages. So, I'll
leave it to you if you want to pursue this further by preparing a patch
or just filing an RFE. Or just leave it as is. Either way is fine with
me, I just wanted to mention it since I noticed it.
Also, just to be clear. I find you changes for "8152118: MinTLABSize
should be less than TLAB max" to be good. Consider them reviewed.
>>> Testing: JPRT, TestOptionsWithRanges.java for all platforms.
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