--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/cms/cmsCardTable.cpp Sat Mar 24 01:08:35 2018 +0100
@@ -0,0 +1,432 @@
+/*
+ * Copyright (c) 2007, 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.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/cms/cmsHeap.hpp"
+#include "gc/shared/cardTableBarrierSet.hpp"
+#include "gc/shared/cardTableRS.hpp"
+#include "gc/shared/collectedHeap.hpp"
+#include "gc/shared/space.inline.hpp"
+#include "memory/allocation.inline.hpp"
+#include "memory/virtualspace.hpp"
+#include "oops/oop.inline.hpp"
+#include "runtime/java.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/orderAccess.inline.hpp"
+#include "runtime/vmThread.hpp"
+
+void CardTableRS::
+non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
+ OopsInGenClosure* cl,
+ CardTableRS* ct,
+ uint n_threads) {
+ assert(n_threads > 0, "expected n_threads > 0");
+ assert(n_threads <= ParallelGCThreads,
+ "n_threads: %u > ParallelGCThreads: %u", n_threads, ParallelGCThreads);
+
+ // Make sure the LNC array is valid for the space.
+ jbyte** lowest_non_clean;
+ uintptr_t lowest_non_clean_base_chunk_index;
+ size_t lowest_non_clean_chunk_size;
+ get_LNC_array_for_space(sp, lowest_non_clean,
+ lowest_non_clean_base_chunk_index,
+ lowest_non_clean_chunk_size);
+
+ uint n_strides = n_threads * ParGCStridesPerThread;
+ SequentialSubTasksDone* pst = sp->par_seq_tasks();
+ // Sets the condition for completion of the subtask (how many threads
+ // need to finish in order to be done).
+ pst->set_n_threads(n_threads);
+ pst->set_n_tasks(n_strides);
+
+ uint stride = 0;
+ while (!pst->is_task_claimed(/* reference */ stride)) {
+ process_stride(sp, mr, stride, n_strides,
+ cl, ct,
+ lowest_non_clean,
+ lowest_non_clean_base_chunk_index,
+ lowest_non_clean_chunk_size);
+ }
+ if (pst->all_tasks_completed()) {
+ // Clear lowest_non_clean array for next time.
+ intptr_t first_chunk_index = addr_to_chunk_index(mr.start());
+ uintptr_t last_chunk_index = addr_to_chunk_index(mr.last());
+ for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) {
+ intptr_t ind = ch - lowest_non_clean_base_chunk_index;
+ assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size,
+ "Bounds error");
+ lowest_non_clean[ind] = NULL;
+ }
+ }
+}
+
+void
+CardTableRS::
+process_stride(Space* sp,
+ MemRegion used,
+ jint stride, int n_strides,
+ OopsInGenClosure* cl,
+ CardTableRS* ct,
+ jbyte** lowest_non_clean,
+ uintptr_t lowest_non_clean_base_chunk_index,
+ size_t lowest_non_clean_chunk_size) {
+ // We go from higher to lower addresses here; it wouldn't help that much
+ // because of the strided parallelism pattern used here.
+
+ // Find the first card address of the first chunk in the stride that is
+ // at least "bottom" of the used region.
+ jbyte* start_card = byte_for(used.start());
+ jbyte* end_card = byte_after(used.last());
+ uintptr_t start_chunk = addr_to_chunk_index(used.start());
+ uintptr_t start_chunk_stride_num = start_chunk % n_strides;
+ jbyte* chunk_card_start;
+
+ if ((uintptr_t)stride >= start_chunk_stride_num) {
+ chunk_card_start = (jbyte*)(start_card +
+ (stride - start_chunk_stride_num) *
+ ParGCCardsPerStrideChunk);
+ } else {
+ // Go ahead to the next chunk group boundary, then to the requested stride.
+ chunk_card_start = (jbyte*)(start_card +
+ (n_strides - start_chunk_stride_num + stride) *
+ ParGCCardsPerStrideChunk);
+ }
+
+ while (chunk_card_start < end_card) {
+ // Even though we go from lower to higher addresses below, the
+ // strided parallelism can interleave the actual processing of the
+ // dirty pages in various ways. For a specific chunk within this
+ // stride, we take care to avoid double scanning or missing a card
+ // by suitably initializing the "min_done" field in process_chunk_boundaries()
+ // below, together with the dirty region extension accomplished in
+ // DirtyCardToOopClosure::do_MemRegion().
+ jbyte* chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk;
+ // Invariant: chunk_mr should be fully contained within the "used" region.
+ MemRegion chunk_mr = MemRegion(addr_for(chunk_card_start),
+ chunk_card_end >= end_card ?
+ used.end() : addr_for(chunk_card_end));
+ assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)");
+ assert(used.contains(chunk_mr), "chunk_mr should be subset of used");
+
+ // This function is used by the parallel card table iteration.
+ const bool parallel = true;
+
+ DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),
+ cl->gen_boundary(),
+ parallel);
+ ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel);
+
+
+ // Process the chunk.
+ process_chunk_boundaries(sp,
+ dcto_cl,
+ chunk_mr,
+ used,
+ lowest_non_clean,
+ lowest_non_clean_base_chunk_index,
+ lowest_non_clean_chunk_size);
+
+ // We want the LNC array updates above in process_chunk_boundaries
+ // to be visible before any of the card table value changes as a
+ // result of the dirty card iteration below.
+ OrderAccess::storestore();
+
+ // We want to clear the cards: clear_cl here does the work of finding
+ // contiguous dirty ranges of cards to process and clear.
+ clear_cl.do_MemRegion(chunk_mr);
+
+ // Find the next chunk of the stride.
+ chunk_card_start += ParGCCardsPerStrideChunk * n_strides;
+ }
+}
+
+void
+CardTableRS::
+process_chunk_boundaries(Space* sp,
+ DirtyCardToOopClosure* dcto_cl,
+ MemRegion chunk_mr,
+ MemRegion used,
+ jbyte** lowest_non_clean,
+ uintptr_t lowest_non_clean_base_chunk_index,
+ size_t lowest_non_clean_chunk_size)
+{
+ // We must worry about non-array objects that cross chunk boundaries,
+ // because such objects are both precisely and imprecisely marked:
+ // .. if the head of such an object is dirty, the entire object
+ // needs to be scanned, under the interpretation that this
+ // was an imprecise mark
+ // .. if the head of such an object is not dirty, we can assume
+ // precise marking and it's efficient to scan just the dirty
+ // cards.
+ // In either case, each scanned reference must be scanned precisely
+ // once so as to avoid cloning of a young referent. For efficiency,
+ // our closures depend on this property and do not protect against
+ // double scans.
+
+ uintptr_t start_chunk_index = addr_to_chunk_index(chunk_mr.start());
+ assert(start_chunk_index >= lowest_non_clean_base_chunk_index, "Bounds error.");
+ uintptr_t cur_chunk_index = start_chunk_index - lowest_non_clean_base_chunk_index;
+
+ // First, set "our" lowest_non_clean entry, which would be
+ // used by the thread scanning an adjoining left chunk with
+ // a non-array object straddling the mutual boundary.
+ // Find the object that spans our boundary, if one exists.
+ // first_block is the block possibly straddling our left boundary.
+ HeapWord* first_block = sp->block_start(chunk_mr.start());
+ assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),
+ "First chunk should always have a co-initial block");
+ // Does the block straddle the chunk's left boundary, and is it
+ // a non-array object?
+ if (first_block < chunk_mr.start() // first block straddles left bdry
+ && sp->block_is_obj(first_block) // first block is an object
+ && !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied)
+ || oop(first_block)->is_typeArray())) {
+ // Find our least non-clean card, so that a left neighbor
+ // does not scan an object straddling the mutual boundary
+ // too far to the right, and attempt to scan a portion of
+ // that object twice.
+ jbyte* first_dirty_card = NULL;
+ jbyte* last_card_of_first_obj =
+ byte_for(first_block + sp->block_size(first_block) - 1);
+ jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
+ jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());
+ jbyte* last_card_to_check =
+ (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,
+ (intptr_t) last_card_of_first_obj);
+ // Note that this does not need to go beyond our last card
+ // if our first object completely straddles this chunk.
+ for (jbyte* cur = first_card_of_cur_chunk;
+ cur <= last_card_to_check; cur++) {
+ jbyte val = *cur;
+ if (card_will_be_scanned(val)) {
+ first_dirty_card = cur; break;
+ } else {
+ assert(!card_may_have_been_dirty(val), "Error");
+ }
+ }
+ if (first_dirty_card != NULL) {
+ assert(cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error.");
+ assert(lowest_non_clean[cur_chunk_index] == NULL,
+ "Write exactly once : value should be stable hereafter for this round");
+ lowest_non_clean[cur_chunk_index] = first_dirty_card;
+ }
+ } else {
+ // In this case we can help our neighbor by just asking them
+ // to stop at our first card (even though it may not be dirty).
+ assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");
+ jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
+ lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;
+ }
+
+ // Next, set our own max_to_do, which will strictly/exclusively bound
+ // the highest address that we will scan past the right end of our chunk.
+ HeapWord* max_to_do = NULL;
+ if (chunk_mr.end() < used.end()) {
+ // This is not the last chunk in the used region.
+ // What is our last block? We check the first block of
+ // the next (right) chunk rather than strictly check our last block
+ // because it's potentially more efficient to do so.
+ HeapWord* const last_block = sp->block_start(chunk_mr.end());
+ assert(last_block <= chunk_mr.end(), "In case this property changes.");
+ if ((last_block == chunk_mr.end()) // our last block does not straddle boundary
+ || !sp->block_is_obj(last_block) // last_block isn't an object
+ || oop(last_block)->is_objArray() // last_block is an array (precisely marked)
+ || oop(last_block)->is_typeArray()) {
+ max_to_do = chunk_mr.end();
+ } else {
+ assert(last_block < chunk_mr.end(), "Tautology");
+ // It is a non-array object that straddles the right boundary of this chunk.
+ // last_obj_card is the card corresponding to the start of the last object
+ // in the chunk. Note that the last object may not start in
+ // the chunk.
+ jbyte* const last_obj_card = byte_for(last_block);
+ const jbyte val = *last_obj_card;
+ if (!card_will_be_scanned(val)) {
+ assert(!card_may_have_been_dirty(val), "Error");
+ // The card containing the head is not dirty. Any marks on
+ // subsequent cards still in this chunk must have been made
+ // precisely; we can cap processing at the end of our chunk.
+ max_to_do = chunk_mr.end();
+ } else {
+ // The last object must be considered dirty, and extends onto the
+ // following chunk. Look for a dirty card in that chunk that will
+ // bound our processing.
+ jbyte* limit_card = NULL;
+ const size_t last_block_size = sp->block_size(last_block);
+ jbyte* const last_card_of_last_obj =
+ byte_for(last_block + last_block_size - 1);
+ jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());
+ // This search potentially goes a long distance looking
+ // for the next card that will be scanned, terminating
+ // at the end of the last_block, if no earlier dirty card
+ // is found.
+ assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,
+ "last card of next chunk may be wrong");
+ for (jbyte* cur = first_card_of_next_chunk;
+ cur <= last_card_of_last_obj; cur++) {
+ const jbyte val = *cur;
+ if (card_will_be_scanned(val)) {
+ limit_card = cur; break;
+ } else {
+ assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");
+ }
+ }
+ if (limit_card != NULL) {
+ max_to_do = addr_for(limit_card);
+ assert(limit_card != NULL && max_to_do != NULL, "Error");
+ } else {
+ // The following is a pessimistic value, because it's possible
+ // that a dirty card on a subsequent chunk has been cleared by
+ // the time we get to look at it; we'll correct for that further below,
+ // using the LNC array which records the least non-clean card
+ // before cards were cleared in a particular chunk.
+ limit_card = last_card_of_last_obj;
+ max_to_do = last_block + last_block_size;
+ assert(limit_card != NULL && max_to_do != NULL, "Error");
+ }
+ assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,
+ "Bounds error.");
+ // It is possible that a dirty card for the last object may have been
+ // cleared before we had a chance to examine it. In that case, the value
+ // will have been logged in the LNC for that chunk.
+ // We need to examine as many chunks to the right as this object
+ // covers. However, we need to bound this checking to the largest
+ // entry in the LNC array: this is because the heap may expand
+ // after the LNC array has been created but before we reach this point,
+ // and the last block in our chunk may have been expanded to include
+ // the expansion delta (and possibly subsequently allocated from, so
+ // it wouldn't be sufficient to check whether that last block was
+ // or was not an object at this point).
+ uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
+ - lowest_non_clean_base_chunk_index;
+ const uintptr_t last_chunk_index = addr_to_chunk_index(used.last())
+ - lowest_non_clean_base_chunk_index;
+ if (last_chunk_index_to_check > last_chunk_index) {
+ assert(last_block + last_block_size > used.end(),
+ "Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"
+ " does not exceed used.end() = " PTR_FORMAT ","
+ " yet last_chunk_index_to_check " INTPTR_FORMAT
+ " exceeds last_chunk_index " INTPTR_FORMAT,
+ p2i(last_block), p2i(last_block + last_block_size),
+ p2i(used.end()),
+ last_chunk_index_to_check, last_chunk_index);
+ assert(sp->used_region().end() > used.end(),
+ "Expansion did not happen: "
+ "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",
+ p2i(sp->used_region().start()), p2i(sp->used_region().end()),
+ p2i(used.start()), p2i(used.end()));
+ last_chunk_index_to_check = last_chunk_index;
+ }
+ for (uintptr_t lnc_index = cur_chunk_index + 1;
+ lnc_index <= last_chunk_index_to_check;
+ lnc_index++) {
+ jbyte* lnc_card = lowest_non_clean[lnc_index];
+ if (lnc_card != NULL) {
+ // we can stop at the first non-NULL entry we find
+ if (lnc_card <= limit_card) {
+ limit_card = lnc_card;
+ max_to_do = addr_for(limit_card);
+ assert(limit_card != NULL && max_to_do != NULL, "Error");
+ }
+ // In any case, we break now
+ break;
+ } // else continue to look for a non-NULL entry if any
+ }
+ assert(limit_card != NULL && max_to_do != NULL, "Error");
+ }
+ assert(max_to_do != NULL, "OOPS 1 !");
+ }
+ assert(max_to_do != NULL, "OOPS 2!");
+ } else {
+ max_to_do = used.end();
+ }
+ assert(max_to_do != NULL, "OOPS 3!");
+ // Now we can set the closure we're using so it doesn't to beyond
+ // max_to_do.
+ dcto_cl->set_min_done(max_to_do);
+#ifndef PRODUCT
+ dcto_cl->set_last_bottom(max_to_do);
+#endif
+}
+
+void
+CardTableRS::
+get_LNC_array_for_space(Space* sp,
+ jbyte**& lowest_non_clean,
+ uintptr_t& lowest_non_clean_base_chunk_index,
+ size_t& lowest_non_clean_chunk_size) {
+
+ int i = find_covering_region_containing(sp->bottom());
+ MemRegion covered = _covered[i];
+ size_t n_chunks = chunks_to_cover(covered);
+
+ // Only the first thread to obtain the lock will resize the
+ // LNC array for the covered region. Any later expansion can't affect
+ // the used_at_save_marks region.
+ // (I observed a bug in which the first thread to execute this would
+ // resize, and then it would cause "expand_and_allocate" that would
+ // increase the number of chunks in the covered region. Then a second
+ // thread would come and execute this, see that the size didn't match,
+ // and free and allocate again. So the first thread would be using a
+ // freed "_lowest_non_clean" array.)
+
+ // Do a dirty read here. If we pass the conditional then take the rare
+ // event lock and do the read again in case some other thread had already
+ // succeeded and done the resize.
+ int cur_collection = CMSHeap::heap()->total_collections();
+ // Updated _last_LNC_resizing_collection[i] must not be visible before
+ // _lowest_non_clean and friends are visible. Therefore use acquire/release
+ // to guarantee this on non TSO architecures.
+ if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {
+ MutexLocker x(ParGCRareEvent_lock);
+ // This load_acquire is here for clarity only. The MutexLocker already fences.
+ if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {
+ if (_lowest_non_clean[i] == NULL ||
+ n_chunks != _lowest_non_clean_chunk_size[i]) {
+
+ // Should we delete the old?
+ if (_lowest_non_clean[i] != NULL) {
+ assert(n_chunks != _lowest_non_clean_chunk_size[i],
+ "logical consequence");
+ FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i]);
+ _lowest_non_clean[i] = NULL;
+ }
+ // Now allocate a new one if necessary.
+ if (_lowest_non_clean[i] == NULL) {
+ _lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);
+ _lowest_non_clean_chunk_size[i] = n_chunks;
+ _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());
+ for (int j = 0; j < (int)n_chunks; j++)
+ _lowest_non_clean[i][j] = NULL;
+ }
+ }
+ // Make sure this gets visible only after _lowest_non_clean* was initialized
+ OrderAccess::release_store(&_last_LNC_resizing_collection[i], cur_collection);
+ }
+ }
+ // In any case, now do the initialization.
+ lowest_non_clean = _lowest_non_clean[i];
+ lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];
+ lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i];
+}