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6850869: G1: RSet "scrubbing" scrubs too much

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RSet scrubbing incorrectly deletes RSet entries that point to regions tagged as "continues humongous" due to a race when RSet scrubbing iterates over regions in parallel.

Reviewed-by: apetrusenko, iveresov
This commit is contained in:
Antonios Printezis 2009-06-24 11:42:03 -04:00
parent c8140c1078
commit 3a643c42b0
1 changed files with 44 additions and 9 deletions
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53
hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp
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@ -1233,6 +1233,41 @@ public:
CardTableModRefBS::card_shift);
}
// It takes a region that's not empty (i.e., it has at least one
// live object in it and sets its corresponding bit on the region
// bitmap to 1. If the region is "starts humongous" it will also set
// to 1 the bits on the region bitmap that correspond to its
// associated "continues humongous" regions.
void set_bit_for_region(HeapRegion* hr) {
assert(!hr->continuesHumongous(), "should have filtered those out");
size_t index = hr->hrs_index();
if (!hr->startsHumongous()) {
// Normal (non-humongous) case: just set the bit.
_region_bm->par_at_put((BitMap::idx_t) index, true);
} else {
// Starts humongous case: calculate how many regions are part of
// this humongous region and then set the bit range. It might
// have been a bit more efficient to look at the object that
// spans these humongous regions to calculate their number from
// the object's size. However, it's a good idea to calculate
// this based on the metadata itself, and not the region
// contents, so that this code is not aware of what goes into
// the humongous regions (in case this changes in the future).
G1CollectedHeap* g1h = G1CollectedHeap::heap();
size_t end_index = index + 1;
while (index < g1h->n_regions()) {
HeapRegion* chr = g1h->region_at(index);
if (!chr->continuesHumongous()) {
break;
}
end_index += 1;
}
_region_bm->par_at_put_range((BitMap::idx_t) index,
(BitMap::idx_t) end_index, true);
}
}
bool doHeapRegion(HeapRegion* hr) {
if (_co_tracker != NULL)
_co_tracker->update();
@ -1241,13 +1276,13 @@ public:
_start_vtime_sec = os::elapsedVTime();
if (hr->continuesHumongous()) {
HeapRegion* hum_start = hr->humongous_start_region();
// If the head region of the humongous region has been determined
// to be alive, then all the tail regions should be marked
// such as well.
if (_region_bm->at(hum_start->hrs_index())) {
_region_bm->par_at_put(hr->hrs_index(), 1);
}
// We will ignore these here and process them when their
// associated "starts humongous" region is processed (see
// set_bit_for_heap_region()). Note that we cannot rely on their
// associated "starts humongous" region to have their bit set to
// 1 since, due to the region chunking in the parallel region
// iteration, a "continues humongous" region might be visited
// before its associated "starts humongous".
return false;
}
@ -1343,14 +1378,14 @@ public:
intptr_t(uintptr_t(tp) >> CardTableModRefBS::card_shift);
mark_card_num_range(start_card_num, last_card_num);
// This definitely means the region has live objects.
_region_bm->par_at_put(hr->hrs_index(), 1);
set_bit_for_region(hr);
}
}
hr->add_to_marked_bytes(marked_bytes);
// Update the live region bitmap.
if (marked_bytes > 0) {
_region_bm->par_at_put(hr->hrs_index(), 1);
set_bit_for_region(hr);
}
hr->set_top_at_conc_mark_count(nextTop);
_tot_live += hr->next_live_bytes();