Mercurial > hg > truffle
diff src/share/vm/memory/cardTableRS.cpp @ 3287:c48ad6ab8bdf
7037276: Unnecessary double traversal of dirty card windows
Summary: Short-circuited an unnecessary double traversal of dirty card windows when iterating younger refs. Also renamed some cardtable methods for more clarity.
Reviewed-by: jmasa, stefank, poonam
author | ysr |
---|---|
date | Wed, 20 Apr 2011 19:19:30 -0700 |
parents | c69b1043dfb1 |
children | 1f4413413144 |
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--- a/src/share/vm/memory/cardTableRS.cpp Tue Apr 19 15:46:59 2011 -0400 +++ b/src/share/vm/memory/cardTableRS.cpp Wed Apr 20 19:19:30 2011 -0700 @@ -105,107 +105,111 @@ 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; - } +inline bool ClearNoncleanCardWrapper::clear_card(jbyte* entry) { + if (_is_par) { + return clear_card_parallel(entry); + } else { + return clear_card_serial(entry); + } +} + +inline bool ClearNoncleanCardWrapper::clear_card_parallel(jbyte* entry) { + 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."); } - return true; + } 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 { - 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; + 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; +} -public: - ClearNoncleanCardWrapper(MemRegionClosure* dirty_card_closure, - CardTableRS* ct) : + +inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) { + 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; +} + +ClearNoncleanCardWrapper::ClearNoncleanCardWrapper( + MemRegionClosure* dirty_card_closure, CardTableRS* ct) : _dirty_card_closure(dirty_card_closure), _ct(ct) { _is_par = (SharedHeap::heap()->n_par_threads() > 0); +} + +void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) { + assert(mr.word_size() > 0, "Error"); + assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned"); + // mr.end() may not necessarily be card aligned. + jbyte* cur_entry = _ct->byte_for(mr.last()); + const jbyte* limit = _ct->byte_for(mr.start()); + HeapWord* end_of_non_clean = mr.end(); + HeapWord* start_of_non_clean = end_of_non_clean; + while (cur_entry >= limit) { + HeapWord* cur_hw = _ct->addr_for(cur_entry); + if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) { + // Continue the dirty range by opening the + // dirty window one card to the left. + start_of_non_clean = cur_hw; + } else { + // We hit a "clean" card; process any non-empty + // "dirty" range accumulated so far. + if (start_of_non_clean < end_of_non_clean) { + const MemRegion mrd(start_of_non_clean, end_of_non_clean); + _dirty_card_closure->do_MemRegion(mrd); + } + // Reset the dirty window, while continuing to look + // for the next dirty card that will start a + // new dirty window. + end_of_non_clean = cur_hw; + start_of_non_clean = cur_hw; + } + // Note that "cur_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". + cur_entry--; } - 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); - } + // 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) { + const MemRegion mrd(start_of_non_clean, end_of_non_clean); + _dirty_card_closure->do_MemRegion(mrd); } -}; +} + // clean (by dirty->clean before) ==> cur_younger_gen // dirty ==> cur_youngergen_and_prev_nonclean_card // precleaned ==> cur_youngergen_and_prev_nonclean_card @@ -246,8 +250,8 @@ 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); + _ct_bs->non_clean_card_iterate_possibly_parallel(sp, sp->used_region_at_save_marks(), + dcto_cl, &clear_cl); } void CardTableRS::clear_into_younger(Generation* gen, bool clear_perm) {