RFR: 8210857: Allow retiring TLABs and collecting statistics in parallel
Erik Österlund
erik.osterlund at oracle.com
Thu Sep 20 10:23:26 UTC 2018
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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