[16] RFR(T) 8248426: NMT: VirtualMemoryTracker::split_reserved_region() does not properly update summary counting

[Zhengyu Gu]

Hi Thomas,

On 6/29/20 2:30 AM, Thomas Stüfe wrote:
> 
>     - splitting the reserved region
> 
>     Could we not simply add the call
>     to VirtualMemorySummary::record_released_memory(size,
>     reserved_rgn->flag()); to
>     VirtualMemoryTracker::split_reserved_region() instead?

I assume you could. Then removing and adding reserved region calls
are asymmetrical.

For this particular case, remove_released_region() turns out to be 
exactly what you suggested, since reserved_rgn->same_region(addr, size) 
== true.

...
VirtualMemorySummary::record_released_memory(size, reserved_rgn->flag());

...

return _reserved_regions->remove(rgn);


Thanks,

-Zhengyu


> 
>     Thanks, Thomas
> 
> 
> 
> 
> 
>     On Fri, Jun 26, 2020 at 10:54 PM Zhengyu Gu <zgu at redhat.com
>     <mailto:zgu at redhat.com>> wrote:
> 
>         Hi,
> 
>         Please review this trivial patch that fixes summary counting in
>         VirtualMemoryTracker::split_reserved_region().
> 
>         The method uses internal method to remove a reserved region,
>         which does
>         not update counting information. It should use high level tracking
>         method VirtualMemoryTracker::remove_released_region() instead.
> 
>         Without patch, NMT summary reports uncategorized memory, e.g.
> 
>         -                   Unknown (reserved=1060416KB, committed=0KB)
>                                       (mmap: reserved=1060416KB,
>         committed=0KB)
> 
> 
> 
> 
>         Bug: https://bugs.openjdk.java.net/browse/JDK-8248426
>         Webrev: http://cr.openjdk.java.net/~zgu/JDK-8248426/webrev.00/
> 
>         Test:
>             hotspot_nmt
>             Submit test in progress
> 
> 
>         Thanks,
> 
>         -Zhengyu
>