RFR: 8233494: Avoid calling MallocTracker::record_malloc and record_free when NMT is off

[Doerr, Martin]

Hi Claes,

this makes sense. Change looks good to me.

Best regards,
Martin


> -----Original Message-----
> From: hotspot-runtime-dev <hotspot-runtime-dev-
> bounces at openjdk.java.net> On Behalf Of Claes Redestad
> Sent: Montag, 4. November 2019 14:54
> To: Hotspot dev runtime <hotspot-runtime-dev at openjdk.java.net>
> Subject: RFR: 8233494: Avoid calling MallocTracker::record_malloc and
> record_free when NMT is off
> 
> Hi,
> 
> this patch removes some small but measurable NMT-related overheads
> when
> when NMT is disabled, by moving NMT_off checks out into MemTracker
> where
> they can be more aggressively inlined.
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8233494
> Webrev: http://cr.openjdk.java.net/~redestad/8233494/open.00/
> 
> Motivation:
> 
> Overhead of calling MallocTracker methods account for ~15-25% of
> instructions retired by os::malloc/realloc/free. On a "Hello World" on
> my laptop (no large pages) we already do roughly 9k os::malloc calls, so
> this improvement means a reduction in instructions retired by ~250k, or
> ~0.2% of the total. There is no discernible difference in behavior or
> overhead for the case when NMT is enabled.
> 
> Testing: tier1-2
> 
> Thanks!
> 
> /Claes