graal-jvmci-8: src/share/vm/memory/cardTableRS.cpp comparison

comparison src/share/vm/memory/cardTableRS.cpp @ 0:a61af66fc99e jdk7-b24

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author	duke
date	Sat, 01 Dec 2007 00:00:00 +0000
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children	73e96e5c30df

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+:a61af66fc99e
+/*
+* Copyright 2001-2006 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+* CA 95054 USA or visit www.sun.com if you need additional information or
+* have any questions.
+*
+*/
+# include "incls/_precompiled.incl"
+# include "incls/_cardTableRS.cpp.incl"
+CardTableRS::CardTableRS(MemRegion whole_heap,
+int max_covered_regions) :
+GenRemSet(&_ct_bs),
+_ct_bs(whole_heap, max_covered_regions),
+_cur_youngergen_card_val(youngergenP1_card)
+{
+_last_cur_val_in_gen = new jbyte[GenCollectedHeap::max_gens + 1];
+if (_last_cur_val_in_gen == NULL) {
+vm_exit_during_initialization("Could not last_cur_val_in_gen array.");
+}
+for (int i = 0; i < GenCollectedHeap::max_gens + 1; i++) {
+_last_cur_val_in_gen[i] = clean_card_val();
+}
+_ct_bs.set_CTRS(this);
+}
+void CardTableRS::resize_covered_region(MemRegion new_region) {
+_ct_bs.resize_covered_region(new_region);
+}
+jbyte CardTableRS::find_unused_youngergenP_card_value() {
+GenCollectedHeap* gch = GenCollectedHeap::heap();
+for (jbyte v = youngergenP1_card;
+v < cur_youngergen_and_prev_nonclean_card;
+v++) {
+bool seen = false;
+for (int g = 0; g < gch->n_gens()+1; g++) {
+if (_last_cur_val_in_gen[g] == v) {
+seen = true;
+break;
+}
+}
+if (!seen) return v;
+}
+ShouldNotReachHere();
+return 0;
+}
+void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {
+// Parallel or sequential, we must always set the prev to equal the
+// last one written.
+if (parallel) {
+// Find a parallel value to be used next.
+jbyte next_val = find_unused_youngergenP_card_value();
+set_cur_youngergen_card_val(next_val);
+} else {
+// In an sequential traversal we will always write youngergen, so that
+// the inline barrier is  correct.
+set_cur_youngergen_card_val(youngergen_card);
+}
+}
+void CardTableRS::younger_refs_iterate(Generation* g,
+OopsInGenClosure* blk) {
+_last_cur_val_in_gen[g->level()+1] = cur_youngergen_card_val();
+g->younger_refs_iterate(blk);
+}
+class ClearNoncleanCardWrapper: public MemRegionClosure {
+MemRegionClosure* _dirty_card_closure;
+CardTableRS* _ct;
+bool _is_par;
+private:
+// Clears the given card, return true if the corresponding card should be
+// processed.
+bool clear_card(jbyte* entry) {
+if (_is_par) {
+while (true) {
+// In the parallel case, we may have to do this several times.
+jbyte entry_val = *entry;
+assert(entry_val != CardTableRS::clean_card_val(),
+"We shouldn't be looking at clean cards, and this should "
+"be the only place they get cleaned.");
+if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)
+|| _ct->is_prev_youngergen_card_val(entry_val)) {
+jbyte res =
+Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);
+if (res == entry_val) {
+break;
+} else {
+assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,
+"The CAS above should only fail if another thread did "
+"a GC write barrier.");
+}
+} else if (entry_val ==
+CardTableRS::cur_youngergen_and_prev_nonclean_card) {
+// Parallelism shouldn't matter in this case.  Only the thread
+// assigned to scan the card should change this value.
+*entry = _ct->cur_youngergen_card_val();
+break;
+} else {
+assert(entry_val == _ct->cur_youngergen_card_val(),
+"Should be the only possibility.");
+// In this case, the card was clean before, and become
+// cur_youngergen only because of processing of a promoted object.
+// We don't have to look at the card.
+return false;
+}
+}
+return true;
+} else {
+jbyte entry_val = *entry;
+assert(entry_val != CardTableRS::clean_card_val(),
+"We shouldn't be looking at clean cards, and this should "
+"be the only place they get cleaned.");
+assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,
+"This should be possible in the sequential case.");
+*entry = CardTableRS::clean_card_val();
+return true;
+}
+}
+public:
+ClearNoncleanCardWrapper(MemRegionClosure* dirty_card_closure,
+CardTableRS* ct) :
+_dirty_card_closure(dirty_card_closure), _ct(ct) {
+_is_par = (SharedHeap::heap()->n_par_threads() > 0);
+}
+void do_MemRegion(MemRegion mr) {
+// We start at the high end of "mr", walking backwards
+// while accumulating a contiguous dirty range of cards in
+// [start_of_non_clean, end_of_non_clean) which we then
+// process en masse.
+HeapWord* end_of_non_clean = mr.end();
+HeapWord* start_of_non_clean = end_of_non_clean;
+jbyte*       entry = _ct->byte_for(mr.last());
+const jbyte* first_entry = _ct->byte_for(mr.start());
+while (entry >= first_entry) {
+HeapWord* cur = _ct->addr_for(entry);
+if (!clear_card(entry)) {
+// We hit a clean card; process any non-empty
+// dirty range accumulated so far.
+if (start_of_non_clean < end_of_non_clean) {
+MemRegion mr2(start_of_non_clean, end_of_non_clean);
+_dirty_card_closure->do_MemRegion(mr2);
+}
+// Reset the dirty window while continuing to
+// look for the next dirty window to process.
+end_of_non_clean = cur;
+start_of_non_clean = end_of_non_clean;
+}
+// Open the left end of the window one card to the left.
+start_of_non_clean = cur;
+// Note that "entry" leads "start_of_non_clean" in
+// its leftward excursion after this point
+// in the loop and, when we hit the left end of "mr",
+// will point off of the left end of the card-table
+// for "mr".
+entry--;
+}
+// If the first card of "mr" was dirty, we will have
+// been left with a dirty window, co-initial with "mr",
+// which we now process.
+if (start_of_non_clean < end_of_non_clean) {
+MemRegion mr2(start_of_non_clean, end_of_non_clean);
+_dirty_card_closure->do_MemRegion(mr2);
+}
+}
+};
+// clean (by dirty->clean before) ==> cur_younger_gen
+// dirty                          ==> cur_youngergen_and_prev_nonclean_card
+// precleaned                     ==> cur_youngergen_and_prev_nonclean_card
+// prev-younger-gen               ==> cur_youngergen_and_prev_nonclean_card
+// cur-younger-gen                ==> cur_younger_gen
+// cur_youngergen_and_prev_nonclean_card ==> no change.
+void CardTableRS::write_ref_field_gc_par(oop* field, oop new_val) {
+jbyte* entry = ct_bs()->byte_for(field);
+do {
+jbyte entry_val = *entry;
+// We put this first because it's probably the most common case.
+if (entry_val == clean_card_val()) {
+// No threat of contention with cleaning threads.
+*entry = cur_youngergen_card_val();
+return;
+} else if (card_is_dirty_wrt_gen_iter(entry_val)
+|| is_prev_youngergen_card_val(entry_val)) {
+// Mark it as both cur and prev youngergen; card cleaning thread will
+// eventually remove the previous stuff.
+jbyte new_val = cur_youngergen_and_prev_nonclean_card;
+jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);
+// Did the CAS succeed?
+if (res == entry_val) return;
+// Otherwise, retry, to see the new value.
+continue;
+} else {
+assert(entry_val == cur_youngergen_and_prev_nonclean_card
+|| entry_val == cur_youngergen_card_val(),
+"should be only possibilities.");
+return;
+}
+} while (true);
+}
+void CardTableRS::younger_refs_in_space_iterate(Space* sp,
+OopsInGenClosure* cl) {
+DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, _ct_bs.precision(),
+cl->gen_boundary());
+ClearNoncleanCardWrapper clear_cl(dcto_cl, this);
+_ct_bs.non_clean_card_iterate(sp, sp->used_region_at_save_marks(),
+dcto_cl, &clear_cl, false);
+}
+void CardTableRS::clear_into_younger(Generation* gen, bool clear_perm) {
+GenCollectedHeap* gch = GenCollectedHeap::heap();
+// Generations younger than gen have been evacuated. We can clear
+// card table entries for gen (we know that it has no pointers
+// to younger gens) and for those below. The card tables for
+// the youngest gen need never be cleared, and those for perm gen
+// will be cleared based on the parameter clear_perm.
+// There's a bit of subtlety in the clear() and invalidate()
+// methods that we exploit here and in invalidate_or_clear()
+// below to avoid missing cards at the fringes. If clear() or
+// invalidate() are changed in the future, this code should
+// be revisited. 20040107.ysr
+Generation* g = gen;
+for(Generation* prev_gen = gch->prev_gen(g);
+prev_gen != NULL;
+g = prev_gen, prev_gen = gch->prev_gen(g)) {
+MemRegion to_be_cleared_mr = g->prev_used_region();
+clear(to_be_cleared_mr);
+}
+// Clear perm gen cards if asked to do so.
+if (clear_perm) {
+MemRegion to_be_cleared_mr = gch->perm_gen()->prev_used_region();
+clear(to_be_cleared_mr);
+}
+}
+void CardTableRS::invalidate_or_clear(Generation* gen, bool younger,
+bool perm) {
+GenCollectedHeap* gch = GenCollectedHeap::heap();
+// For each generation gen (and younger and/or perm)
+// invalidate the cards for the currently occupied part
+// of that generation and clear the cards for the
+// unoccupied part of the generation (if any, making use
+// of that generation's prev_used_region to determine that
+// region). No need to do anything for the youngest
+// generation. Also see note#20040107.ysr above.
+Generation* g = gen;
+for(Generation* prev_gen = gch->prev_gen(g); prev_gen != NULL;
+g = prev_gen, prev_gen = gch->prev_gen(g))  {
+MemRegion used_mr = g->used_region();
+MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
+if (!to_be_cleared_mr.is_empty()) {
+clear(to_be_cleared_mr);
+}
+invalidate(used_mr);
+if (!younger) break;
+}
+// Clear perm gen cards if asked to do so.
+if (perm) {
+g = gch->perm_gen();
+MemRegion used_mr = g->used_region();
+MemRegion to_be_cleared_mr = g->prev_used_region().minus(used_mr);
+if (!to_be_cleared_mr.is_empty()) {
+clear(to_be_cleared_mr);
+}
+invalidate(used_mr);
+}
+}
+class VerifyCleanCardClosure: public OopClosure {
+HeapWord* boundary;
+HeapWord* begin; HeapWord* end;
+public:
+void do_oop(oop* p) {
+HeapWord* jp = (HeapWord*)p;
+if (jp >= begin && jp < end) {
+guarantee(*p == NULL || (HeapWord*)p < boundary
+|| (HeapWord*)(*p) >= boundary,
+"pointer on clean card crosses boundary");
+}
+}
+VerifyCleanCardClosure(HeapWord* b, HeapWord* _begin, HeapWord* _end) :
+boundary(b), begin(_begin), end(_end) {}
+};
+class VerifyCTSpaceClosure: public SpaceClosure {
+CardTableRS* _ct;
+HeapWord* _boundary;
+public:
+VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :
+_ct(ct), _boundary(boundary) {}
+void do_space(Space* s) { _ct->verify_space(s, _boundary); }
+};
+class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {
+CardTableRS* _ct;
+public:
+VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}
+void do_generation(Generation* gen) {
+// Skip the youngest generation.
+if (gen->level() == 0) return;
+// Normally, we're interested in pointers to younger generations.
+VerifyCTSpaceClosure blk(_ct, gen->reserved().start());
+gen->space_iterate(&blk, true);
+}
+};
+void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {
+// We don't need to do young-gen spaces.
+if (s->end() <= gen_boundary) return;
+MemRegion used = s->used_region();
+jbyte* cur_entry = byte_for(used.start());
+jbyte* limit = byte_after(used.last());
+while (cur_entry < limit) {
+if (*cur_entry == CardTableModRefBS::clean_card) {
+jbyte* first_dirty = cur_entry+1;
+while (first_dirty < limit &&
+*first_dirty == CardTableModRefBS::clean_card) {
+first_dirty++;
+}
+// If the first object is a regular object, and it has a
+// young-to-old field, that would mark the previous card.
+HeapWord* boundary = addr_for(cur_entry);
+HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);
+HeapWord* boundary_block = s->block_start(boundary);
+HeapWord* begin = boundary;             // Until proven otherwise.
+HeapWord* start_block = boundary_block; // Until proven otherwise.
+if (boundary_block < boundary) {
+if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {
+oop boundary_obj = oop(boundary_block);
+if (!boundary_obj->is_objArray() &&
+!boundary_obj->is_typeArray()) {
+guarantee(cur_entry > byte_for(used.start()),
+"else boundary would be boundary_block");
+if (*byte_for(boundary_block) != CardTableModRefBS::clean_card) {
+begin = boundary_block + s->block_size(boundary_block);
+start_block = begin;
+}
+}
+}
+}
+// Now traverse objects until end.
+HeapWord* cur = start_block;
+VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);
+while (cur < end) {
+if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {
+oop(cur)->oop_iterate(&verify_blk);
+}
+cur += s->block_size(cur);
+}
+cur_entry = first_dirty;
+} else {
+// We'd normally expect that cur_youngergen_and_prev_nonclean_card
+// is a transient value, that cannot be in the card table
+// except during GC, and thus assert that:
+// guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,
+//        "Illegal CT value");
+// That however, need not hold, as will become clear in the
+// following...
+// We'd normally expect that if we are in the parallel case,
+// we can't have left a prev value (which would be different
+// from the current value) in the card table, and so we'd like to
+// assert that:
+// guarantee(cur_youngergen_card_val() == youngergen_card
+//           || !is_prev_youngergen_card_val(*cur_entry),
+//           "Illegal CT value");
+// That, however, may not hold occasionally, because of
+// CMS or MSC in the old gen. To wit, consider the
+// following two simple illustrative scenarios:
+// (a) CMS: Consider the case where a large object L
+//     spanning several cards is allocated in the old
+//     gen, and has a young gen reference stored in it, dirtying
+//     some interior cards. A young collection scans the card,
+//     finds a young ref and installs a youngergenP_n value.
+//     L then goes dead. Now a CMS collection starts,
+//     finds L dead and sweeps it up. Assume that L is
+//     abutting _unallocated_blk, so _unallocated_blk is
+//     adjusted down to (below) L. Assume further that
+//     no young collection intervenes during this CMS cycle.
+//     The next young gen cycle will not get to look at this
+//     youngergenP_n card since it lies in the unoccupied
+//     part of the space.
+//     Some young collections later the blocks on this
+//     card can be re-allocated either due to direct allocation
+//     or due to absorbing promotions. At this time, the
+//     before-gc verification will fail the above assert.
+// (b) MSC: In this case, an object L with a young reference
+//     is on a card that (therefore) holds a youngergen_n value.
+//     Suppose also that L lies towards the end of the used
+//     the used space before GC. An MSC collection
+//     occurs that compacts to such an extent that this
+//     card is no longer in the occupied part of the space.
+//     Since current code in MSC does not always clear cards
+//     in the unused part of old gen, this stale youngergen_n
+//     value is left behind and can later be covered by
+//     an object when promotion or direct allocation
+//     re-allocates that part of the heap.
+//
+// Fortunately, the presence of such stale card values is
+// "only" a minor annoyance in that subsequent young collections
+// might needlessly scan such cards, but would still never corrupt
+// the heap as a result. However, it's likely not to be a significant
+// performance inhibitor in practice. For instance,
+// some recent measurements with unoccupied cards eagerly cleared
+// out to maintain this invariant, showed next to no
+// change in young collection times; of course one can construct
+// degenerate examples where the cost can be significant.)
+// Note, in particular, that if the "stale" card is modified
+// after re-allocation, it would be dirty, not "stale". Thus,
+// we can never have a younger ref in such a card and it is
+// safe not to scan that card in any collection. [As we see
+// below, we do some unnecessary scanning
+// in some cases in the current parallel scanning algorithm.]
+//
+// The main point below is that the parallel card scanning code
+// deals correctly with these stale card values. There are two main
+// cases to consider where we have a stale "younger gen" value and a
+// "derivative" case to consider, where we have a stale
+// "cur_younger_gen_and_prev_non_clean" value, as will become
+// apparent in the case analysis below.
+// o Case 1. If the stale value corresponds to a younger_gen_n
+//   value other than the cur_younger_gen value then the code
+//   treats this as being tantamount to a prev_younger_gen
+//   card. This means that the card may be unnecessarily scanned.
+//   There are two sub-cases to consider:
+//   o Case 1a. Let us say that the card is in the occupied part
+//     of the generation at the time the collection begins. In
+//     that case the card will be either cleared when it is scanned
+//     for young pointers, or will be set to cur_younger_gen as a
+//     result of promotion. (We have elided the normal case where
+//     the scanning thread and the promoting thread interleave
+//     possibly resulting in a transient
+//     cur_younger_gen_and_prev_non_clean value before settling
+//     to cur_younger_gen. [End Case 1a.]
+//   o Case 1b. Consider now the case when the card is in the unoccupied
+//     part of the space which becomes occupied because of promotions
+//     into it during the current young GC. In this case the card
+//     will never be scanned for young references. The current
+//     code will set the card value to either
+//     cur_younger_gen_and_prev_non_clean or leave
+//     it with its stale value -- because the promotions didn't
+//     result in any younger refs on that card. Of these two
+//     cases, the latter will be covered in Case 1a during
+//     a subsequent scan. To deal with the former case, we need
+//     to further consider how we deal with a stale value of
+//     cur_younger_gen_and_prev_non_clean in our case analysis
+//     below. This we do in Case 3 below. [End Case 1b]
+//   [End Case 1]
+// o Case 2. If the stale value corresponds to cur_younger_gen being
+//   a value not necessarily written by a current promotion, the
+//   card will not be scanned by the younger refs scanning code.
+//   (This is OK since as we argued above such cards cannot contain
+//   any younger refs.) The result is that this value will be
+//   treated as a prev_younger_gen value in a subsequent collection,
+//   which is addressed in Case 1 above. [End Case 2]
+// o Case 3. We here consider the "derivative" case from Case 1b. above
+//   because of which we may find a stale
+//   cur_younger_gen_and_prev_non_clean card value in the table.
+//   Once again, as in Case 1, we consider two subcases, depending
+//   on whether the card lies in the occupied or unoccupied part
+//   of the space at the start of the young collection.
+//   o Case 3a. Let us say the card is in the occupied part of
+//     the old gen at the start of the young collection. In that
+//     case, the card will be scanned by the younger refs scanning
+//     code which will set it to cur_younger_gen. In a subsequent
+//     scan, the card will be considered again and get its final
+//     correct value. [End Case 3a]
+//   o Case 3b. Now consider the case where the card is in the
+//     unoccupied part of the old gen, and is occupied as a result
+//     of promotions during thus young gc. In that case,
+//     the card will not be scanned for younger refs. The presence
+//     of newly promoted objects on the card will then result in
+//     its keeping the value cur_younger_gen_and_prev_non_clean
+//     value, which we have dealt with in Case 3 here. [End Case 3b]
+//   [End Case 3]
+//
+// (Please refer to the code in the helper class
+// ClearNonCleanCardWrapper and in CardTableModRefBS for details.)
+//
+// The informal arguments above can be tightened into a formal
+// correctness proof and it behooves us to write up such a proof,
+// or to use model checking to prove that there are no lingering
+// concerns.
+//
+// Clearly because of Case 3b one cannot bound the time for
+// which a card will retain what we have called a "stale" value.
+// However, one can obtain a Loose upper bound on the redundant
+// work as a result of such stale values. Note first that any
+// time a stale card lies in the occupied part of the space at
+// the start of the collection, it is scanned by younger refs
+// code and we can define a rank function on card values that
+// declines when this is so. Note also that when a card does not
+// lie in the occupied part of the space at the beginning of a
+// young collection, its rank can either decline or stay unchanged.
+// In this case, no extra work is done in terms of redundant
+// younger refs scanning of that card.
+// Then, the case analysis above reveals that, in the worst case,
+// any such stale card will be scanned unnecessarily at most twice.
+//
+// It is nonethelss advisable to try and get rid of some of this
+// redundant work in a subsequent (low priority) re-design of
+// the card-scanning code, if only to simplify the underlying
+// state machine analysis/proof. ysr 1/28/2002. XXX
+cur_entry++;
+}
+}
+}
+void CardTableRS::verify() {
+// At present, we only know how to verify the card table RS for
+// generational heaps.
+VerifyCTGenClosure blk(this);
+CollectedHeap* ch = Universe::heap();
+// We will do the perm-gen portion of the card table, too.
+Generation* pg = SharedHeap::heap()->perm_gen();
+HeapWord* pg_boundary = pg->reserved().start();
+if (ch->kind() == CollectedHeap::GenCollectedHeap) {
+GenCollectedHeap::heap()->generation_iterate(&blk, false);
+_ct_bs.verify();
+// If the old gen collections also collect perm, then we are only
+// interested in perm-to-young pointers, not perm-to-old pointers.
+GenCollectedHeap* gch = GenCollectedHeap::heap();
+CollectorPolicy* cp = gch->collector_policy();
+if (cp->is_mark_sweep_policy() || cp->is_concurrent_mark_sweep_policy()) {
+pg_boundary = gch->get_gen(1)->reserved().start();
+}
+}
+VerifyCTSpaceClosure perm_space_blk(this, pg_boundary);
+SharedHeap::heap()->perm_gen()->space_iterate(&perm_space_blk, true);
+}
+void CardTableRS::verify_empty(MemRegion mr) {
+if (!mr.is_empty()) {
+jbyte* cur_entry = byte_for(mr.start());
+jbyte* limit = byte_after(mr.last());
+for (;cur_entry < limit; cur_entry++) {
+guarantee(*cur_entry == CardTableModRefBS::clean_card,
+"Unexpected dirty card found");
+}
+}
+}

Mercurial > hg > graal-jvmci-8

comparison src/share/vm/memory/cardTableRS.cpp @ 0:a61af66fc99e jdk7-b24