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

[Lindenmaier, Goetz]

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