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

[Zhengyu Gu]

Hi Thomas,

On 7/4/20 1:35 AM, Thomas Stüfe wrote:
> Hi Zhengyu,
> 
> sorry for the wait.

No problem.

> 
> 
> This looks good, but why did you remove the "!same region" condition? I 
> believe that is needed for the case when CDS' first mapping encounters 
> errors, so before it rebuilds CDS at another location it removes (a) all 
> mappings and then (b) the enclosing reservation. (a) should be ignored 
> by NMT but (b) should not. I may be wrong, I have had no coffee yet.
> Cheers, Thomas

In new version, same region is handled in line #470

  470   if (reserved_rgn->same_region(addr, size)) {
  471     return remove_released_region(reserved_rgn);
  472   }

so, !same region is always true.

Thanks,

-Zhengyu

> 
>     Thanks,
> 
>     -Zhengyu
> 
>      >
>      > But if you are still unconvinced, I won't hold you up. The change
>      > certainly works as it is now and is okay for me, it just would
>     not be my
>      > preferred solution.
>      >
>      > Cheers, Thomas
>      >
>      >     Thanks,
>      >
>      >     -Zhengyu
>      >
>      >
>      >      >
>      >      >     Thanks, Thomas
>      >      >
>      >      >
>      >      >
>      >      >
>      >      >
>      >      >     On Fri, Jun 26, 2020 at 10:54 PM Zhengyu Gu
>     <zgu at redhat.com <mailto:zgu at redhat.com>
>      >     <mailto:zgu at redhat.com <mailto:zgu at redhat.com>>
>      >      >     <mailto:zgu at redhat.com <mailto:zgu at redhat.com>
>     <mailto: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
>      >      >
>      >
>