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8155917: Memory access in free regions during G1 full gc causes regressions in SPECjvm2008 scimark.fft,lu,sor,sparse with 9+116 on Linux-x64

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Do not unnecessarily touch the memory of free regions during the compaction phase in G1 full gc causing some OSes to allocate physical memory for them, decreasing performance in some situations.

Reviewed-by: mgerdin, jmasa
This commit is contained in:
Thomas Schatzl 2016-08-30 09:17:49 +02:00
parent 6db26ca5bf
commit 5258f6573c
1 changed files with 4 additions and 3 deletions
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7
hotspot/src/share/vm/gc/shared/space.inline.hpp
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@ -293,10 +293,11 @@ inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
verify_up_to_first_dead(space);
HeapWord* const bottom = space->bottom();
HeapWord* const end_of_live = space->_end_of_live;
assert(space->_first_dead <= end_of_live, "Invariant. _first_dead: " PTR_FORMAT " <= end_of_live: " PTR_FORMAT, p2i(space->_first_dead), p2i(end_of_live));
if (space->_first_dead == end_of_live && !oop(space->bottom())->is_gc_marked()) {
if (space->_first_dead == end_of_live && (bottom == end_of_live || !oop(bottom)->is_gc_marked())) {
// Nothing to compact. The space is either empty or all live object should be left in place.
clear_empty_region(space);
return;
@ -305,8 +306,8 @@ inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
const intx scan_interval = PrefetchScanIntervalInBytes;
const intx copy_interval = PrefetchCopyIntervalInBytes;
assert(space->bottom() < end_of_live, "bottom: " PTR_FORMAT " should be < end_of_live: " PTR_FORMAT, p2i(space->bottom()), p2i(end_of_live));
HeapWord* cur_obj = space->bottom();
assert(bottom < end_of_live, "bottom: " PTR_FORMAT " should be < end_of_live: " PTR_FORMAT, p2i(bottom), p2i(end_of_live));
HeapWord* cur_obj = bottom;
if (space->_first_dead > cur_obj && !oop(cur_obj)->is_gc_marked()) {
// All object before _first_dead can be skipped. They should not be moved.
// A pointer to the first live object is stored at the memory location for _first_dead.