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src/hotspot/share/gc/shared/cardTableModRefBS.cpp
RFE_8195103_reduce_initial_card_marks
/*
! * Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
/*
! * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
***************
#include "gc/shared/genCollectedHeap.hpp"
#include "gc/shared/space.inline.hpp"
#include "logging/log.hpp"
#include "memory/virtualspace.hpp"
#include "oops/oop.inline.hpp"
+ #include "runtime/thread.hpp"
#include "services/memTracker.hpp"
#include "utilities/align.hpp"
#include "utilities/macros.hpp"
// This kind of "BarrierSet" allows a "CollectedHeap" to detect and
***************
_byte_map_size(0),
_covered(NULL),
_committed(NULL),
_cur_covered_regions(0),
_byte_map(NULL),
! byte_map_base(NULL)
{
assert((uintptr_t(_whole_heap.start()) & (card_size - 1)) == 0, "heap must start at card boundary");
assert((uintptr_t(_whole_heap.end()) & (card_size - 1)) == 0, "heap must end at card boundary");
assert(card_size <= 512, "card_size must be less than 512"); // why?
_byte_map_size(0),
_covered(NULL),
_committed(NULL),
_cur_covered_regions(0),
_byte_map(NULL),
! byte_map_base(NULL),
! _defer_initial_card_mark(false)
{
assert((uintptr_t(_whole_heap.start()) & (card_size - 1)) == 0, "heap must start at card boundary");
assert((uintptr_t(_whole_heap.end()) & (card_size - 1)) == 0, "heap must end at card boundary");
assert(card_size <= 512, "card_size must be less than 512"); // why?
***************
vm_exit_during_initialization("Could not allocate card table covered region set.");
}
}
void CardTableModRefBS::initialize() {
+ initialize_deferred_card_mark_barriers();
_guard_index = cards_required(_whole_heap.word_size()) - 1;
_last_valid_index = _guard_index - 1;
_byte_map_size = compute_byte_map_size();
***************
void CardTableModRefBS::print_on(outputStream* st) const {
st->print_cr("Card table byte_map: [" INTPTR_FORMAT "," INTPTR_FORMAT "] byte_map_base: " INTPTR_FORMAT,
p2i(_byte_map), p2i(_byte_map + _byte_map_size), p2i(byte_map_base));
}
+
+ // Helper for ReduceInitialCardMarks. For performance,
+ // compiled code may elide card-marks for initializing stores
+ // to a newly allocated object along the fast-path. We
+ // compensate for such elided card-marks as follows:
+ // (a) Generational, non-concurrent collectors, such as
+ // GenCollectedHeap(ParNew,DefNew,Tenured) and
+ // ParallelScavengeHeap(ParallelGC, ParallelOldGC)
+ // need the card-mark if and only if the region is
+ // in the old gen, and do not care if the card-mark
+ // succeeds or precedes the initializing stores themselves,
+ // so long as the card-mark is completed before the next
+ // scavenge. For all these cases, we can do a card mark
+ // at the point at which we do a slow path allocation
+ // in the old gen, i.e. in this call.
+ // (b) GenCollectedHeap(ConcurrentMarkSweepGeneration) requires
+ // in addition that the card-mark for an old gen allocated
+ // object strictly follow any associated initializing stores.
+ // In these cases, the memRegion remembered below is
+ // used to card-mark the entire region either just before the next
+ // slow-path allocation by this thread or just before the next scavenge or
+ // CMS-associated safepoint, whichever of these events happens first.
+ // (The implicit assumption is that the object has been fully
+ // initialized by this point, a fact that we assert when doing the
+ // card-mark.)
+ // (c) G1CollectedHeap(G1) uses two kinds of write barriers. When a
+ // G1 concurrent marking is in progress an SATB (pre-write-)barrier
+ // is used to remember the pre-value of any store. Initializing
+ // stores will not need this barrier, so we need not worry about
+ // compensating for the missing pre-barrier here. Turning now
+ // to the post-barrier, we note that G1 needs a RS update barrier
+ // which simply enqueues a (sequence of) dirty cards which may
+ // optionally be refined by the concurrent update threads. Note
+ // that this barrier need only be applied to a non-young write,
+ // but, like in CMS, because of the presence of concurrent refinement
+ // (much like CMS' precleaning), must strictly follow the oop-store.
+ // Thus, using the same protocol for maintaining the intended
+ // invariants turns out, serendepitously, to be the same for both
+ // G1 and CMS.
+ //
+ // For any future collector, this code should be reexamined with
+ // that specific collector in mind, and the documentation above suitably
+ // extended and updated.
+ void CardTableModRefBS::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) {
+ if (!ReduceInitialCardMarks) {
+ return;
+ }
+ // If a previous card-mark was deferred, flush it now.
+ flush_deferred_card_mark_barrier(thread);
+ if (new_obj->is_typeArray() || is_in_young(new_obj)) {
+ // Arrays of non-references don't need a post-barrier.
+ // The deferred_card_mark region should be empty
+ // following the flush above.
+ assert(thread->deferred_card_mark().is_empty(), "Error");
+ } else {
+ MemRegion mr((HeapWord*)new_obj, new_obj->size());
+ assert(!mr.is_empty(), "Error");
+ if (_defer_initial_card_mark) {
+ // Defer the card mark
+ thread->set_deferred_card_mark(mr);
+ } else {
+ // Do the card mark
+ write_region(mr);
+ }
+ }
+ }
+
+ void CardTableModRefBS::initialize_deferred_card_mark_barriers() {
+ // Used for ReduceInitialCardMarks (when COMPILER2 or JVMCI is used);
+ // otherwise remains unused.
+ #if defined(COMPILER2) || INCLUDE_JVMCI
+ _defer_initial_card_mark = is_server_compilation_mode_vm() && ReduceInitialCardMarks && can_elide_tlab_store_barriers()
+ && (DeferInitialCardMark || card_mark_must_follow_store());
+ #else
+ assert(_defer_initial_card_mark == false, "Who would set it?");
+ #endif
+ }
+
+ void CardTableModRefBS::flush_deferred_card_mark_barrier(JavaThread* thread) {
+ #if defined(COMPILER2) || INCLUDE_JVMCI
+ MemRegion deferred = thread->deferred_card_mark();
+ if (!deferred.is_empty()) {
+ assert(_defer_initial_card_mark, "Otherwise should be empty");
+ {
+ // Verify that the storage points to a parsable object in heap
+ DEBUG_ONLY(oop old_obj = oop(deferred.start());)
+ assert(!is_in_young(old_obj),
+ "Else should have been filtered in on_slowpath_allocation_exit()");
+ assert(oopDesc::is_oop(old_obj, true), "Not an oop");
+ assert(deferred.word_size() == (size_t)(old_obj->size()),
+ "Mismatch: multiple objects?");
+ }
+ write_region(deferred);
+ // "Clear" the deferred_card_mark field
+ thread->set_deferred_card_mark(MemRegion());
+ }
+ assert(thread->deferred_card_mark().is_empty(), "invariant");
+ #else
+ assert(!_defer_initial_card_mark, "Should be false");
+ assert(thread->deferred_card_mark().is_empty(), "Should be empty");
+ #endif
+ }
+
+ void CardTableModRefBS::flush_deferred_barriers(JavaThread* thread) {
+ // The deferred store barriers must all have been flushed to the
+ // card-table (or other remembered set structure) before GC starts
+ // processing the card-table (or other remembered set).
+ flush_deferred_card_mark_barrier(thread);
+ }
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