RFR: 8210857: Allow retiring TLABs and collecting statistics in parallel

Per Liden per.liden at oracle.com
Thu Sep 20 10:21:22 UTC 2018

Thanks Erik!


On 09/20/2018 12:23 PM, Erik Österlund wrote:
> Hi Per,
> Looks good.
> Thanks,
> /Erik
> On 2018-09-20 12:04, Per Liden wrote:
>> On 09/18/2018 10:16 PM, Per Liden wrote:
>>> On 09/18/2018 10:13 PM, Per Liden wrote:
>>>> There is currently no good way of retiring TLABs and collecting 
>>>> their statistics in parallel. The current code for doing this also 
>>>> traverses the thread list twice, which is unnecessary. I propose 
>>>> that we adjust the TLAB API to allow this to be done in parallel, in 
>>>> a single pass.
>>>> A few notes on this patch:
>>>> * The GlobalTLABStats class is restructured into the 
>>>> ThreadLocalAllocStats class to allow for a more flexible way of 
>>>> collected statistics when retiring TLABs (flexible in the sense that 
>>>> it allows for parallel operations).
>>>> * The TLAB API is slightly adjusted. The "make_parsable(bool 
>>>> retire_tlab)" is broken into two functions, "make_parsable()" to 
>>>> just make a TLAB parsable, and "retire(ThreadLocalAllocStats* 
>>>> stats)" to retire and optionally collects statistics.
>>>> * GCs are unaffected by this change, in the sense that they continue 
>>>> to call CollectedHeap::ensure_parsability(). However, all GCs will 
>>>> benefit from now doing a single pass over the thread list instead of 
>>>> two to retire and collect stats.
>>>> * This is the last patch in my series of TLAB related patches. The 
>>>> remaining patches only touch ZGC to actually retire/resize/remap 
>>>> TLABs in parallel.
>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8210857
>>>> Webrev: http://cr.openjdk.java.net/~pliden/8210857/webrev.0
>>> Testing: Passed tier{1,2,3,4,5,6} on linux-x86_64 (product and debug)
>> Discussed with Erik and Stefan off-line, which resulted in the 
>> following adjustment. This adjustment actually fixes a long standing 
>> bug we've had, when make_parsable(false) is called and ZeroTLAB is 
>> true, in which case we actually retire the TLAB but failed to call 
>> Thread::incr_allocated_bytes() to update the number of allocated bytes.
>> Diff: http://cr.openjdk.java.net/~pliden/8210857/webrev.0vs1
>> Full: http://cr.openjdk.java.net/~pliden/8210857/webrev.1
>> /Per

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