| /* |
| * 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/cmsCardTable.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.hpp" |
| #include "runtime/vmThread.hpp" |
| |
| CMSCardTable::CMSCardTable(MemRegion whole_heap) : |
| CardTableRS(whole_heap, CMSPrecleaningEnabled /* scanned_concurrently */) { |
| } |
| |
| // Returns the number of chunks necessary to cover "mr". |
| size_t CMSCardTable::chunks_to_cover(MemRegion mr) { |
| return (size_t)(addr_to_chunk_index(mr.last()) - |
| addr_to_chunk_index(mr.start()) + 1); |
| } |
| |
| // Returns the index of the chunk in a stride which |
| // covers the given address. |
| uintptr_t CMSCardTable::addr_to_chunk_index(const void* addr) { |
| uintptr_t card = (uintptr_t) byte_for(addr); |
| return card / ParGCCardsPerStrideChunk; |
| } |
| |
| void CMSCardTable:: |
| 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 |
| CMSCardTable:: |
| 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 |
| CMSCardTable:: |
| 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 |
| CMSCardTable:: |
| 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]; |
| } |
| |
| #ifdef ASSERT |
| void CMSCardTable::verify_used_region_at_save_marks(Space* sp) const { |
| MemRegion ur = sp->used_region(); |
| MemRegion urasm = sp->used_region_at_save_marks(); |
| |
| if (!ur.contains(urasm)) { |
| log_warning(gc)("CMS+ParNew: Did you forget to call save_marks()? " |
| "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in " |
| "[" PTR_FORMAT ", " PTR_FORMAT ")", |
| p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end())); |
| MemRegion ur2 = sp->used_region(); |
| MemRegion urasm2 = sp->used_region_at_save_marks(); |
| if (!ur.equals(ur2)) { |
| log_warning(gc)("CMS+ParNew: Flickering used_region()!!"); |
| } |
| if (!urasm.equals(urasm2)) { |
| log_warning(gc)("CMS+ParNew: Flickering used_region_at_save_marks()!!"); |
| } |
| ShouldNotReachHere(); |
| } |
| } |
| #endif // ASSERT |
