/* * Copyright (c) 2001, 2012, 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_implementation/shared/parGCAllocBuffer.hpp" #include "memory/sharedHeap.hpp" #include "oops/arrayOop.hpp" #include "oops/oop.inline.hpp" ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) : _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL), _end(NULL), _hard_end(NULL), _retained(false), _retained_filler(), _allocated(0), _wasted(0) { assert (min_size() > AlignmentReserve, "Inconsistency!"); // arrayOopDesc::header_size depends on command line initialization. FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT)); AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0; } size_t ParGCAllocBuffer::FillerHeaderSize; // If the minimum object size is greater than MinObjAlignment, we can // end up with a shard at the end of the buffer that's smaller than // the smallest object. We can't allow that because the buffer must // look like it's full of objects when we retire it, so we make // sure we have enough space for a filler int array object. size_t ParGCAllocBuffer::AlignmentReserve; void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) { assert(!retain || end_of_gc, "Can only retain at GC end."); if (_retained) { // If the buffer had been retained shorten the previous filler object. assert(_retained_filler.end() <= _top, "INVARIANT"); CollectedHeap::fill_with_object(_retained_filler); // Wasted space book-keeping, otherwise (normally) done in invalidate() _wasted += _retained_filler.word_size(); _retained = false; } assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained."); if (_top < _hard_end) { CollectedHeap::fill_with_object(_top, _hard_end); if (!retain) { invalidate(); } else { // Is there wasted space we'd like to retain for the next GC? if (pointer_delta(_end, _top) > FillerHeaderSize) { _retained = true; _retained_filler = MemRegion(_top, FillerHeaderSize); _top = _top + FillerHeaderSize; } else { invalidate(); } } } } void ParGCAllocBuffer::flush_stats(PLABStats* stats) { assert(ResizePLAB, "Wasted work"); stats->add_allocated(_allocated); stats->add_wasted(_wasted); stats->add_unused(pointer_delta(_end, _top)); } // Compute desired plab size and latch result for later // use. This should be called once at the end of parallel // scavenge; it clears the sensor accumulators. void PLABStats::adjust_desired_plab_sz(uint no_of_gc_workers) { assert(ResizePLAB, "Not set"); assert(is_object_aligned(max_size()) && min_size() <= max_size(), "PLAB clipping computation may be incorrect"); if (_allocated == 0) { assert(_unused == 0, err_msg("Inconsistency in PLAB stats: " "_allocated: "SIZE_FORMAT", " "_wasted: "SIZE_FORMAT", " "_unused: "SIZE_FORMAT", " "_used : "SIZE_FORMAT, _allocated, _wasted, _unused, _used)); _allocated = 1; } double wasted_frac = (double)_unused/(double)_allocated; size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/ TargetPLABWastePct); if (target_refills == 0) { target_refills = 1; } _used = _allocated - _wasted - _unused; size_t plab_sz = _used/(target_refills*no_of_gc_workers); if (PrintPLAB) gclog_or_tty->print(" (plab_sz = " SIZE_FORMAT " ", plab_sz); // Take historical weighted average _filter.sample(plab_sz); // Clip from above and below, and align to object boundary plab_sz = MAX2(min_size(), (size_t)_filter.average()); plab_sz = MIN2(max_size(), plab_sz); plab_sz = align_object_size(plab_sz); // Latch the result if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = " SIZE_FORMAT ") ", plab_sz); _desired_plab_sz = plab_sz; // Now clear the accumulators for next round: // note this needs to be fixed in the case where we // are retaining across scavenges. FIX ME !!! XXX _allocated = 0; _wasted = 0; _unused = 0; } #ifndef PRODUCT void ParGCAllocBuffer::print() { gclog_or_tty->print("parGCAllocBuffer: _bottom: %p _top: %p _end: %p _hard_end: %p" "_retained: %c _retained_filler: [%p,%p)\n", _bottom, _top, _end, _hard_end, "FT"[_retained], _retained_filler.start(), _retained_filler.end()); } #endif // !PRODUCT const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords = MIN2(CardTableModRefBS::par_chunk_heapword_alignment(), ((size_t)Generation::GenGrain)/HeapWordSize); const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes = MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize, (size_t)Generation::GenGrain); ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz, BlockOffsetSharedArray* bsa) : ParGCAllocBuffer(word_sz), _bsa(bsa), _bt(bsa, MemRegion(_bottom, _hard_end)), _true_end(_hard_end) {} // The buffer comes with its own BOT, with a shared (obviously) underlying // BlockOffsetSharedArray. We manipulate this BOT in the normal way // as we would for any contiguous space. However, on occasion we // need to do some buffer surgery at the extremities before we // start using the body of the buffer for allocations. Such surgery // (as explained elsewhere) is to prevent allocation on a card that // is in the process of being walked concurrently by another GC thread. // When such surgery happens at a point that is far removed (to the // right of the current allocation point, top), we use the "contig" // parameter below to directly manipulate the shared array without // modifying the _next_threshold state in the BOT. void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr, bool contig) { CollectedHeap::fill_with_object(mr); if (contig) { _bt.alloc_block(mr.start(), mr.end()); } else { _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end()); } } HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) { HeapWord* res = NULL; if (_true_end > _hard_end) { assert((HeapWord*)align_size_down(intptr_t(_hard_end), ChunkSizeInBytes) == _hard_end, "or else _true_end should be equal to _hard_end"); assert(_retained, "or else _true_end should be equal to _hard_end"); assert(_retained_filler.end() <= _top, "INVARIANT"); CollectedHeap::fill_with_object(_retained_filler); if (_top < _hard_end) { fill_region_with_block(MemRegion(_top, _hard_end), true); } HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords); _retained_filler = MemRegion(_hard_end, FillerHeaderSize); _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size()); _top = _retained_filler.end(); _hard_end = next_hard_end; _end = _hard_end - AlignmentReserve; res = ParGCAllocBuffer::allocate(word_sz); if (res != NULL) { _bt.alloc_block(res, word_sz); } } return res; } void ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) { ParGCAllocBuffer::undo_allocation(obj, word_sz); // This may back us up beyond the previous threshold, so reset. _bt.set_region(MemRegion(_top, _hard_end)); _bt.initialize_threshold(); } void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) { assert(!retain || end_of_gc, "Can only retain at GC end."); if (_retained) { // We're about to make the retained_filler into a block. _bt.BlockOffsetArray::alloc_block(_retained_filler.start(), _retained_filler.end()); } // Reset _hard_end to _true_end (and update _end) if (retain && _hard_end != NULL) { assert(_hard_end <= _true_end, "Invariant."); _hard_end = _true_end; _end = MAX2(_top, _hard_end - AlignmentReserve); assert(_end <= _hard_end, "Invariant."); } _true_end = _hard_end; HeapWord* pre_top = _top; ParGCAllocBuffer::retire(end_of_gc, retain); // Now any old _retained_filler is cut back to size, the free part is // filled with a filler object, and top is past the header of that // object. if (retain && _top < _end) { assert(end_of_gc && retain, "Or else retain should be false."); // If the lab does not start on a card boundary, we don't want to // allocate onto that card, since that might lead to concurrent // allocation and card scanning, which we don't support. So we fill // the first card with a garbage object. size_t first_card_index = _bsa->index_for(pre_top); HeapWord* first_card_start = _bsa->address_for_index(first_card_index); if (first_card_start < pre_top) { HeapWord* second_card_start = _bsa->inc_by_region_size(first_card_start); // Ensure enough room to fill with the smallest block second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve); // If the end is already in the first card, don't go beyond it! // Or if the remainder is too small for a filler object, gobble it up. if (_hard_end < second_card_start || pointer_delta(_hard_end, second_card_start) < AlignmentReserve) { second_card_start = _hard_end; } if (pre_top < second_card_start) { MemRegion first_card_suffix(pre_top, second_card_start); fill_region_with_block(first_card_suffix, true); } pre_top = second_card_start; _top = pre_top; _end = MAX2(_top, _hard_end - AlignmentReserve); } // If the lab does not end on a card boundary, we don't want to // allocate onto that card, since that might lead to concurrent // allocation and card scanning, which we don't support. So we fill // the last card with a garbage object. size_t last_card_index = _bsa->index_for(_hard_end); HeapWord* last_card_start = _bsa->address_for_index(last_card_index); if (last_card_start < _hard_end) { // Ensure enough room to fill with the smallest block last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve); // If the top is already in the last card, don't go back beyond it! // Or if the remainder is too small for a filler object, gobble it up. if (_top > last_card_start || pointer_delta(last_card_start, _top) < AlignmentReserve) { last_card_start = _top; } if (last_card_start < _hard_end) { MemRegion last_card_prefix(last_card_start, _hard_end); fill_region_with_block(last_card_prefix, false); } _hard_end = last_card_start; _end = MAX2(_top, _hard_end - AlignmentReserve); _true_end = _hard_end; assert(_end <= _hard_end, "Invariant."); } // At this point: // 1) we had a filler object from the original top to hard_end. // 2) We've filled in any partial cards at the front and back. if (pre_top < _hard_end) { // Now we can reset the _bt to do allocation in the given area. MemRegion new_filler(pre_top, _hard_end); fill_region_with_block(new_filler, false); _top = pre_top + ParGCAllocBuffer::FillerHeaderSize; // If there's no space left, don't retain. if (_top >= _end) { _retained = false; invalidate(); return; } _retained_filler = MemRegion(pre_top, _top); _bt.set_region(MemRegion(_top, _hard_end)); _bt.initialize_threshold(); assert(_bt.threshold() > _top, "initialize_threshold failed!"); // There may be other reasons for queries into the middle of the // filler object. When such queries are done in parallel with // allocation, bad things can happen, if the query involves object // iteration. So we ensure that such queries do not involve object // iteration, by putting another filler object on the boundaries of // such queries. One such is the object spanning a parallel card // chunk boundary. // "chunk_boundary" is the address of the first chunk boundary less // than "hard_end". HeapWord* chunk_boundary = (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes); assert(chunk_boundary < _hard_end, "Or else above did not work."); assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve, "Consequence of last card handling above."); if (_top <= chunk_boundary) { assert(_true_end == _hard_end, "Invariant."); while (_top <= chunk_boundary) { assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve, "Consequence of last card handling above."); _bt.BlockOffsetArray::alloc_block(chunk_boundary, _hard_end); CollectedHeap::fill_with_object(chunk_boundary, _hard_end); _hard_end = chunk_boundary; chunk_boundary -= ChunkSizeInWords; } _end = _hard_end - AlignmentReserve; assert(_top <= _end, "Invariant."); // Now reset the initial filler chunk so it doesn't overlap with // the one(s) inserted above. MemRegion new_filler(pre_top, _hard_end); fill_region_with_block(new_filler, false); } } else { _retained = false; invalidate(); } } else { assert(!end_of_gc || (!_retained && _true_end == _hard_end), "Checking."); } assert(_end <= _hard_end, "Invariant."); assert(_top < _end || _top == _hard_end, "Invariant"); }