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

[Yumin Qi]

HI, Zhengyu

   Looks good to me!


Thanks

Yumin

On 7/7/20 10:13 AM, Zhengyu Gu wrote:
> The change is no longer trivial, may I get a second review?
>
> Thanks,
>
> -Zhengyu
>
> On 7/7/20 9:34 AM, Thomas Stüfe wrote:
>> Hi Zhengyu,
>>
>> okay, I get it now. Thank you. Reviewed from my side.
>>
>> Cheers, Thomas
>>
>> On Tue, Jul 7, 2020 at 1:53 PM Zhengyu Gu <zgu at redhat.com 
>> <mailto:zgu at redhat.com>> wrote:
>>
>>     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>>>
>>      >      >      >     <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 <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
>>      >      >      >
>>      >      >
>>      >
>>
>