RFR (7xS): 8177044: Remove _scan_top from HeapRegion

[Thomas Schatzl]

Hi Kim and Sangheon,

On Tue, 2017-05-09 at 11:12 -0700, sangheon wrote:
> Hi Thomas,
> 
> On 05/05/2017 05:13 AM, Thomas Schatzl wrote:
> > 
> > Hi all,
> > 
> >    recent reviews have made changes necessary to parts of the
> > changeset
> > chain.
> > 
> > Here is a list of links to updated webrevs. Since they have
> > apparently
> > not been reviewed yet, I simply overwrote the old webrevs.
> > 
> > JDK-8177044: Remove _scan_top from HeapRegion
> > http://cr.openjdk.java.net/~tschatzl/8177044/webrev/
> Looks good to me.
> And agree to Kim about retaining the comment.
> 
> src/share/vm/gc/g1/g1RemSet.cpp
>   765   if (scan_limit <= start) {
>   766     // If the trimmed region is empty, the card must be stale.
>   767     return false;
> 

  thanks for your review.

For reference, here is the comment I intend to push:

--- old/src/share/vm/gc/g1/g1RemSet.cpp	2017-05-11
16:14:56.054517736 +0200
+++ new/src/share/vm/gc/g1/g1RemSet.cpp	2017-05-11
16:14:55.951514554 +0200
@@ -735,6 +735,7 @@
 
   HeapWord* scan_limit = _scan_state->scan_top(r->hrm_index());
   if (scan_limit <= start) {
+    // If the card starts above the area in the region containing
objects to scan, skip it.
     return false;
   }
 
because the original comment is wrong now.

New Webrevs:
http://cr.openjdk.java.net/~tschatzl/8177044/webrev.0_to_1/ (diff)
http://cr.openjdk.java.net/~tschatzl/8177044/webrev.1/ (full)

Thanks again for your reviews,
  Thomas