1.1 --- a/src/share/vm/gc_implementation/g1/satbQueue.cpp Wed Apr 15 12:16:01 2015 -0400
1.2 +++ b/src/share/vm/gc_implementation/g1/satbQueue.cpp Wed Apr 15 16:37:57 2015 -0400
1.3 @@ -1,5 +1,5 @@
1.4 /*
1.5 - * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
1.6 + * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
1.7 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.8 *
1.9 * This code is free software; you can redistribute it and/or modify it
1.10 @@ -35,30 +35,67 @@
1.11 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
1.12
1.13 void ObjPtrQueue::flush() {
1.14 - // The buffer might contain refs into the CSet. We have to filter it
1.15 - // first before we flush it, otherwise we might end up with an
1.16 - // enqueued buffer with refs into the CSet which breaks our invariants.
1.17 + // Filter now to possibly save work later. If filtering empties the
1.18 + // buffer then flush_impl can deallocate the buffer.
1.19 filter();
1.20 flush_impl();
1.21 }
1.22
1.23 -// This method removes entries from an SATB buffer that will not be
1.24 -// useful to the concurrent marking threads. An entry is removed if it
1.25 -// satisfies one of the following conditions:
1.26 +// Return true if a SATB buffer entry refers to an object that
1.27 +// requires marking.
1.28 //
1.29 -// * it points to an object outside the G1 heap (G1's concurrent
1.30 -// marking only visits objects inside the G1 heap),
1.31 -// * it points to an object that has been allocated since marking
1.32 -// started (according to SATB those objects do not need to be
1.33 -// visited during marking), or
1.34 -// * it points to an object that has already been marked (no need to
1.35 -// process it again).
1.36 +// The entry must point into the G1 heap. In particular, it must not
1.37 +// be a NULL pointer. NULL pointers are pre-filtered and never
1.38 +// inserted into a SATB buffer.
1.39 //
1.40 -// The rest of the entries will be retained and are compacted towards
1.41 -// the top of the buffer. Note that, because we do not allow old
1.42 -// regions in the CSet during marking, all objects on the CSet regions
1.43 -// are young (eden or survivors) and therefore implicitly live. So any
1.44 -// references into the CSet will be removed during filtering.
1.45 +// An entry that is below the NTAMS pointer for the containing heap
1.46 +// region requires marking. Such an entry must point to a valid object.
1.47 +//
1.48 +// An entry that is at least the NTAMS pointer for the containing heap
1.49 +// region might be any of the following, none of which should be marked.
1.50 +//
1.51 +// * A reference to an object allocated since marking started.
1.52 +// According to SATB, such objects are implicitly kept live and do
1.53 +// not need to be dealt with via SATB buffer processing.
1.54 +//
1.55 +// * A reference to a young generation object. Young objects are
1.56 +// handled separately and are not marked by concurrent marking.
1.57 +//
1.58 +// * A stale reference to a young generation object. If a young
1.59 +// generation object reference is recorded and not filtered out
1.60 +// before being moved by a young collection, the reference becomes
1.61 +// stale.
1.62 +//
1.63 +// * A stale reference to an eagerly reclaimed humongous object. If a
1.64 +// humongous object is recorded and then reclaimed, the reference
1.65 +// becomes stale.
1.66 +//
1.67 +// The stale reference cases are implicitly handled by the NTAMS
1.68 +// comparison. Because of the possibility of stale references, buffer
1.69 +// processing must be somewhat circumspect and not assume entries
1.70 +// in an unfiltered buffer refer to valid objects.
1.71 +
1.72 +inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
1.73 + // Includes rejection of NULL pointers.
1.74 + assert(heap->is_in_reserved(entry),
1.75 + err_msg("Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry)));
1.76 +
1.77 + HeapRegion* region = heap->heap_region_containing_raw(entry);
1.78 + assert(region != NULL, err_msg("No region for " PTR_FORMAT, p2i(entry)));
1.79 + if (entry >= region->next_top_at_mark_start()) {
1.80 + return false;
1.81 + }
1.82 +
1.83 + assert(((oop)entry)->is_oop(true /* ignore mark word */),
1.84 + err_msg("Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry)));
1.85 +
1.86 + return true;
1.87 +}
1.88 +
1.89 +// This method removes entries from a SATB buffer that will not be
1.90 +// useful to the concurrent marking threads. Entries are retained if
1.91 +// they require marking and are not already marked. Retained entries
1.92 +// are compacted toward the top of the buffer.
1.93
1.94 void ObjPtrQueue::filter() {
1.95 G1CollectedHeap* g1h = G1CollectedHeap::heap();
1.96 @@ -80,26 +117,25 @@
1.97 assert(i > 0, "we should have at least one more entry to process");
1.98 i -= oopSize;
1.99 debug_only(entries += 1;)
1.100 - oop* p = (oop*) &buf[byte_index_to_index((int) i)];
1.101 - oop obj = *p;
1.102 + void** p = &buf[byte_index_to_index((int) i)];
1.103 + void* entry = *p;
1.104 // NULL the entry so that unused parts of the buffer contain NULLs
1.105 // at the end. If we are going to retain it we will copy it to its
1.106 // final place. If we have retained all entries we have visited so
1.107 // far, we'll just end up copying it to the same place.
1.108 *p = NULL;
1.109
1.110 - bool retain = g1h->is_obj_ill(obj);
1.111 - if (retain) {
1.112 + if (requires_marking(entry, g1h) && !g1h->isMarkedNext((oop)entry)) {
1.113 assert(new_index > 0, "we should not have already filled up the buffer");
1.114 new_index -= oopSize;
1.115 assert(new_index >= i,
1.116 "new_index should never be below i, as we alwaysr compact 'up'");
1.117 - oop* new_p = (oop*) &buf[byte_index_to_index((int) new_index)];
1.118 + void** new_p = &buf[byte_index_to_index((int) new_index)];
1.119 assert(new_p >= p, "the destination location should never be below "
1.120 "the source as we always compact 'up'");
1.121 assert(*new_p == NULL,
1.122 "we should have already cleared the destination location");
1.123 - *new_p = obj;
1.124 + *new_p = entry;
1.125 debug_only(retained += 1;)
1.126 }
1.127 }
1.128 @@ -186,17 +222,6 @@
1.129 }
1.130 #endif // PRODUCT
1.131
1.132 -#ifdef ASSERT
1.133 -void ObjPtrQueue::verify_oops_in_buffer() {
1.134 - if (_buf == NULL) return;
1.135 - for (size_t i = _index; i < _sz; i += oopSize) {
1.136 - oop obj = (oop)_buf[byte_index_to_index((int)i)];
1.137 - assert(obj != NULL && obj->is_oop(true /* ignore mark word */),
1.138 - "Not an oop");
1.139 - }
1.140 -}
1.141 -#endif
1.142 -
1.143 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
1.144 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
1.145 #endif // _MSC_VER
1.146 @@ -216,7 +241,6 @@
1.147 }
1.148
1.149 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
1.150 - DEBUG_ONLY(t->satb_mark_queue().verify_oops_in_buffer();)
1.151 t->satb_mark_queue().handle_zero_index();
1.152 }
1.153
