RFR(xs): 8202074: Metaspace: If humongous chunk is added to SpaceManager, previous current chunk may not get retired correctly.

[Thomas Stüfe]

Thank you Goetz!

Change is pushed.

On Tue, Apr 24, 2018 at 12:21 PM, Lindenmaier, Goetz
<goetz.lindenmaier at sap.com> wrote:
> Hi Thomas,
>
> the change looks good, thanks.
>
> One minor nit: please rename
> 3413     bool make_current_chunk = true;
> to "make_chunk_current" or, as in add_chunk, just "make_current".
> No new webrev needed.
>
> Best regards,
>   Goetz.
>
>
>
>> -----Original Message-----
>> From: hotspot-runtime-dev [mailto:hotspot-runtime-dev-
>> bounces at openjdk.java.net] On Behalf Of Thomas Stüfe
>> Sent: Freitag, 20. April 2018 09:54
>> To: Hotspot dev runtime <hotspot-runtime-dev at openjdk.java.net>
>> Subject: RFR(xs): 8202074: Metaspace: If humongous chunk is added to
>> SpaceManager, previous current chunk may not get retired correctly.
>>
>> Hi all,
>>
>> may I have reviews for this fix please:
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8202074
>> webrev: http://cr.openjdk.java.net/~stuefe/webrevs/8202074-metaspace-
>> retire-after-humongous-chunks-are-
>> allocated/webrev.00/webrev/src/hotspot/share/memory/metaspace.cpp.u
>> diff.html
>>
>> When a humongous chunk is added to SpaceManager
>> (SpaceManager::add_chunk(chunk, make_current=true), we make it the
>> current chunk.
>>
>> But we do not correctly retire the old chunk. This leads to the
>> remainder of the used space in the old chunk being wasted.
>>
>> The obvious smallest-possible fix would be this:
>>
>> --- a/src/hotspot/share/memory/metaspace.cpp Mon Apr 16 14:29:27 2018
>> +0530
>> +++ b/src/hotspot/share/memory/metaspace.cpp Fri Apr 20 06:55:04 2018
>> +0200
>> @@ -3573,6 +3573,7 @@
>>      // chunk.
>>      if (make_current) {
>>        // Set as the current chunk but otherwise treat as a humongous chunk.
>> +      retire_current_chunk();
>>        set_current_chunk(new_chunk);
>>      }
>>      // Link at head.  The _current_chunk only points to a humongous chunk for
>>
>> However, I decided to clean the code up a bit and make it more
>> readable. In SpaceManager::add_chunk(), treatment of the non-humongous
>> chunks and humongous chunks is almost identical, beside the fact that
>> non-humongous new chunks were always made current and the argument
>> flag "make_current" was only honored for humongous chunks.
>>
>> I changed that. I simplified SpaceManager::add_chunk() by removing the
>> extra treatment for humongous chunks, instead moving the humongous
>> chunk related decision up to SpaceManager::grow_and_allocate(),
>> together with a clear comment. That has the side effect that
>> SpaceManager::add_chunk(chunk, make_current) now always honors the
>> make_current flag.
>>
>> Thank you, Thomas