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8241920: G1: Lazily initialize OtherRegionsTable::_coarse_map

Reviewed-by: tschatzl, eosterlund
  • Loading branch information
cl4es committed Apr 9, 2020
1 parent 1364505 commit 36f22938ed358837894659b4b4b2005b2e903939
Showing with 22 additions and 7 deletions.
  1. +19 −7 src/hotspot/share/gc/g1/heapRegionRemSet.cpp
  2. +3 −0 src/hotspot/share/gc/g1/heapRegionRemSet.hpp
@@ -69,7 +69,7 @@ OtherRegionsTable::OtherRegionsTable(Mutex* m) :
_g1h(G1CollectedHeap::heap()),
_m(m),
_num_occupied(0),
_coarse_map(G1CollectedHeap::heap()->max_regions(), mtGC),
_coarse_map(mtGC),
_n_coarse_entries(0),
_fine_grain_regions(NULL),
_n_fine_entries(0),
@@ -132,7 +132,7 @@ void OtherRegionsTable::add_reference(OopOrNarrowOopStar from, uint tid) {
RegionIdx_t from_hrm_ind = (RegionIdx_t) from_hr->hrm_index();

// If the region is already coarsened, return.
if (_coarse_map.at(from_hrm_ind)) {
if (is_region_coarsened(from_hrm_ind)) {
assert(contains_reference(from), "We just found " PTR_FORMAT " in the Coarse table", p2i(from));
return;
}
@@ -226,7 +226,6 @@ PerRegionTable* OtherRegionsTable::delete_region_table(size_t& added_by_deleted)
PerRegionTable* max = NULL;
jint max_occ = 0;
PerRegionTable** max_prev = NULL;
size_t max_ind;

size_t i = _fine_eviction_start;
for (size_t k = 0; k < _fine_eviction_sample_size; k++) {
@@ -244,7 +243,6 @@ PerRegionTable* OtherRegionsTable::delete_region_table(size_t& added_by_deleted)
if (max == NULL || cur_occ > max_occ) {
max = cur;
max_prev = prev;
max_ind = i;
max_occ = cur_occ;
}
prev = cur->collision_list_next_addr();
@@ -265,7 +263,15 @@ PerRegionTable* OtherRegionsTable::delete_region_table(size_t& added_by_deleted)

// Set the corresponding coarse bit.
size_t max_hrm_index = (size_t) max->hr()->hrm_index();
if (!_coarse_map.at(max_hrm_index)) {
if (_n_coarse_entries == 0) {
// This will lazily initialize an uninitialized bitmap
_coarse_map.reinitialize(G1CollectedHeap::heap()->max_regions());
_coarse_map.at_put(max_hrm_index, true);
// Release store guarantees that the bitmap has initialized before any
// concurrent reader will ever see a non-zero value for _n_coarse_entries
// (when read with load_acquire)
Atomic::release_store(&_n_coarse_entries, _n_coarse_entries + 1);
} else if (!_coarse_map.at(max_hrm_index)) {
_coarse_map.at_put(max_hrm_index, true);
_n_coarse_entries++;
}
@@ -344,19 +350,25 @@ bool OtherRegionsTable::contains_reference_locked(OopOrNarrowOopStar from) const
HeapRegion* hr = _g1h->heap_region_containing(from);
RegionIdx_t hr_ind = (RegionIdx_t) hr->hrm_index();
// Is this region in the coarse map?
if (_coarse_map.at(hr_ind)) return true;
if (is_region_coarsened(hr_ind)) return true;

PerRegionTable* prt = find_region_table(hr_ind & _mod_max_fine_entries_mask,
hr);
if (prt != NULL) {
return prt->contains_reference(from);

} else {
CardIdx_t card_index = card_within_region(from, hr);
return _sparse_table.contains_card(hr_ind, card_index);
}
}

// A load_acquire on _n_coarse_entries - coupled with the release_store in
// delete_region_table - guarantees we don't access _coarse_map before
// it's been properly initialized.
bool OtherRegionsTable::is_region_coarsened(RegionIdx_t from_hrm_ind) const {
return Atomic::load_acquire(&_n_coarse_entries) > 0 && _coarse_map.at(from_hrm_ind);
}

HeapRegionRemSet::HeapRegionRemSet(G1BlockOffsetTable* bot,
HeapRegion* hr)
: _bot(bot),
@@ -153,6 +153,9 @@ class OtherRegionsTable {

// Clear the entire contents of this remembered set.
void clear();

// Safe for use by concurrent readers outside _m
bool is_region_coarsened(RegionIdx_t from_hrm_ind) const;
};

class PerRegionTable: public CHeapObj<mtGC> {

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