jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp@e7d0505c8a30 (annotated)

src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp@e7d0505c8a30 (annotated)

src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp

Fri, 10 Oct 2014 15:51:58 +0200

author: tschatzl
date: Fri, 10 Oct 2014 15:51:58 +0200
changeset 7257: e7d0505c8a30
parent 7256: 0fcaab91d485
child 7535: 7ae4e26cb1e0
child 9697: cfe3264deba4
permissions: -rw-r--r--

8059758: Footprint regressions with JDK-8038423
Summary: Changes in JDK-8038423 always initialize (zero out) virtual memory used for auxiliary data structures. This causes a footprint regression for G1 in startup benchmarks. This is because they do not touch that memory at all, so the operating system does not actually commit these pages. The fix is to, if the initialization value of the data structures matches the default value of just committed memory (=0), do not do anything.
Reviewed-by: jwilhelm, brutisso

 /*
  * Copyright (c) 2001, 2014, 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.
  *
  */
 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP
 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP
 #include "gc_implementation/g1/g1RegionToSpaceMapper.hpp"
 #include "memory/memRegion.hpp"
 #include "runtime/virtualspace.hpp"
 #include "utilities/globalDefinitions.hpp"
 // The CollectedHeap type requires subtypes to implement a method
 // "block_start".  For some subtypes, notably generational
 // systems using card-table-based write barriers, the efficiency of this
 // operation may be important.  Implementations of the "BlockOffsetArray"
 // class may be useful in providing such efficient implementations.
 //
 // While generally mirroring the structure of the BOT for GenCollectedHeap,
 // the following types are tailored more towards G1's uses; these should,
 // however, be merged back into a common BOT to avoid code duplication
 // and reduce maintenance overhead.
 //
 //    G1BlockOffsetTable (abstract)
 //    -- G1BlockOffsetArray                (uses G1BlockOffsetSharedArray)
 //       -- G1BlockOffsetArrayContigSpace
 //
 // A main impediment to the consolidation of this code might be the
 // effect of making some of the block_start*() calls non-const as
 // below. Whether that might adversely affect performance optimizations
 // that compilers might normally perform in the case of non-G1
 // collectors needs to be carefully investigated prior to any such
 // consolidation.
 // Forward declarations
 class G1BlockOffsetSharedArray;
 class G1OffsetTableContigSpace;
 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
   friend class VMStructs;
 protected:
   // These members describe the region covered by the table.
   // The space this table is covering.
   HeapWord* _bottom;    // == reserved.start
   HeapWord* _end;       // End of currently allocated region.
 public:
   // Initialize the table to cover the given space.
   // The contents of the initial table are undefined.
   G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
     _bottom(bottom), _end(end)
     {
       assert(_bottom <= _end, "arguments out of order");
     }
   // Note that the committed size of the covered space may have changed,
   // so the table size might also wish to change.
   virtual void resize(size_t new_word_size) = 0;
   virtual void set_bottom(HeapWord* new_bottom) {
     assert(new_bottom <= _end,
            err_msg("new_bottom (" PTR_FORMAT ") > _end (" PTR_FORMAT ")",
                    p2i(new_bottom), p2i(_end)));
     _bottom = new_bottom;
     resize(pointer_delta(_end, _bottom));
   }
   // Requires "addr" to be contained by a block, and returns the address of
   // the start of that block.  (May have side effects, namely updating of
   // shared array entries that "point" too far backwards.  This can occur,
   // for example, when LAB allocation is used in a space covered by the
   // table.)
   virtual HeapWord* block_start_unsafe(const void* addr) = 0;
   // Same as above, but does not have any of the possible side effects
   // discussed above.
   virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
   // Returns the address of the start of the block containing "addr", or
   // else "null" if it is covered by no block.  (May have side effects,
   // namely updating of shared array entries that "point" too far
   // backwards.  This can occur, for example, when lab allocation is used
   // in a space covered by the table.)
   inline HeapWord* block_start(const void* addr);
   // Same as above, but does not have any of the possible side effects
   // discussed above.
   inline HeapWord* block_start_const(const void* addr) const;
 };
 class G1BlockOffsetSharedArrayMappingChangedListener : public G1MappingChangedListener {
  public:
   virtual void on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
     // Nothing to do. The BOT is hard-wired to be part of the HeapRegion, and we cannot
     // retrieve it here since this would cause firing of several asserts. The code
     // executed after commit of a region already needs to do some re-initialization of
     // the HeapRegion, so we combine that.
   }
 };
 // This implementation of "G1BlockOffsetTable" divides the covered region
 // into "N"-word subregions (where "N" = 2^"LogN".  An array with an entry
 // for each such subregion indicates how far back one must go to find the
 // start of the chunk that includes the first word of the subregion.
 //
 // Each BlockOffsetArray is owned by a Space.  However, the actual array
 // may be shared by several BlockOffsetArrays; this is useful
 // when a single resizable area (such as a generation) is divided up into
 // several spaces in which contiguous allocation takes place,
 // such as, for example, in G1 or in the train generation.)
 // Here is the shared array type.
 class G1BlockOffsetSharedArray: public CHeapObj<mtGC> {
   friend class G1BlockOffsetArray;
   friend class G1BlockOffsetArrayContigSpace;
   friend class VMStructs;
 private:
   G1BlockOffsetSharedArrayMappingChangedListener _listener;
   // The reserved region covered by the shared array.
   MemRegion _reserved;
   // End of the current committed region.
   HeapWord* _end;
   // Array for keeping offsets for retrieving object start fast given an
   // address.
   u_char* _offset_array;          // byte array keeping backwards offsets
   void check_offset(size_t offset, const char* msg) const {
     assert(offset <= N_words,
            err_msg("%s - "
                    "offset: " SIZE_FORMAT ", N_words: " UINT32_FORMAT,
                    msg, offset, N_words));
   }
   // Bounds checking accessors:
   // For performance these have to devolve to array accesses in product builds.
   inline u_char offset_array(size_t index) const;
   void set_offset_array_raw(size_t index, u_char offset) {
     _offset_array[index] = offset;
   }
   inline void set_offset_array(size_t index, u_char offset);
   inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
   inline void set_offset_array(size_t left, size_t right, u_char offset);
   bool is_card_boundary(HeapWord* p) const;
 public:
   // Return the number of slots needed for an offset array
   // that covers mem_region_words words.
   static size_t compute_size(size_t mem_region_words) {
     size_t number_of_slots = (mem_region_words / N_words);
     return ReservedSpace::allocation_align_size_up(number_of_slots);
   }
   enum SomePublicConstants {
     LogN = 9,
     LogN_words = LogN - LogHeapWordSize,
     N_bytes = 1 << LogN,
     N_words = 1 << LogN_words
   };
   // Initialize the table to cover from "base" to (at least)
   // "base + init_word_size".  In the future, the table may be expanded
   // (see "resize" below) up to the size of "_reserved" (which must be at
   // least "init_word_size".) The contents of the initial table are
   // undefined; it is the responsibility of the constituent
   // G1BlockOffsetTable(s) to initialize cards.
   G1BlockOffsetSharedArray(MemRegion heap, G1RegionToSpaceMapper* storage);
   // Return the appropriate index into "_offset_array" for "p".
   inline size_t index_for(const void* p) const;
   inline size_t index_for_raw(const void* p) const;
   // Return the address indicating the start of the region corresponding to
   // "index" in "_offset_array".
   inline HeapWord* address_for_index(size_t index) const;
   // Variant of address_for_index that does not check the index for validity.
   inline HeapWord* address_for_index_raw(size_t index) const {
     return _reserved.start() + (index << LogN_words);
   }
 };
 // And here is the G1BlockOffsetTable subtype that uses the array.
 class G1BlockOffsetArray: public G1BlockOffsetTable {
   friend class G1BlockOffsetSharedArray;
   friend class G1BlockOffsetArrayContigSpace;
   friend class VMStructs;
 private:
   enum SomePrivateConstants {
     N_words = G1BlockOffsetSharedArray::N_words,
     LogN    = G1BlockOffsetSharedArray::LogN
   };
   // This is the array, which can be shared by several BlockOffsetArray's
   // servicing different
   G1BlockOffsetSharedArray* _array;
   // The space that owns this subregion.
   G1OffsetTableContigSpace* _gsp;
   // The portion [_unallocated_block, _sp.end()) of the space that
   // is a single block known not to contain any objects.
   // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
   HeapWord* _unallocated_block;
   // Sets the entries
   // corresponding to the cards starting at "start" and ending at "end"
   // to point back to the card before "start": the interval [start, end)
   // is right-open.
   void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
   // Same as above, except that the args here are a card _index_ interval
   // that is closed: [start_index, end_index]
   void set_remainder_to_point_to_start_incl(size_t start, size_t end);
 protected:
   G1OffsetTableContigSpace* gsp() const { return _gsp; }
   inline size_t block_size(const HeapWord* p) const;
   // Returns the address of a block whose start is at most "addr".
   // If "has_max_index" is true, "assumes "max_index" is the last valid one
   // in the array.
   inline HeapWord* block_at_or_preceding(const void* addr,
                                          bool has_max_index,
                                          size_t max_index) const;
   // "q" is a block boundary that is <= "addr"; "n" is the address of the
   // next block (or the end of the space.)  Return the address of the
   // beginning of the block that contains "addr".  Does so without side
   // effects (see, e.g., spec of  block_start.)
   inline HeapWord*
   forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
                                          const void* addr) const;
   // "q" is a block boundary that is <= "addr"; return the address of the
   // beginning of the block that contains "addr".  May have side effects
   // on "this", by updating imprecise entries.
   inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
                                                     const void* addr);
   // "q" is a block boundary that is <= "addr"; "n" is the address of the
   // next block (or the end of the space.)  Return the address of the
   // beginning of the block that contains "addr".  May have side effects
   // on "this", by updating imprecise entries.
   HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
                                                   HeapWord* n,
                                                   const void* addr);
   // Requires that "*threshold_" be the first array entry boundary at or
   // above "blk_start", and that "*index_" be the corresponding array
   // index.  If the block starts at or crosses "*threshold_", records
   // "blk_start" as the appropriate block start for the array index
   // starting at "*threshold_", and for any other indices crossed by the
   // block.  Updates "*threshold_" and "*index_" to correspond to the first
   // index after the block end.
   void alloc_block_work2(HeapWord** threshold_, size_t* index_,
                          HeapWord* blk_start, HeapWord* blk_end);
 public:
   // The space may not have it's bottom and top set yet, which is why the
   // region is passed as a parameter. The elements of the array are
   // initialized to zero.
   G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr);
   // Note: this ought to be part of the constructor, but that would require
   // "this" to be passed as a parameter to a member constructor for
   // the containing concrete subtype of Space.
   // This would be legal C++, but MS VC++ doesn't allow it.
   void set_space(G1OffsetTableContigSpace* sp);
   // Resets the covered region to one with the same _bottom as before but
   // the "new_word_size".
   void resize(size_t new_word_size);
   virtual HeapWord* block_start_unsafe(const void* addr);
   virtual HeapWord* block_start_unsafe_const(const void* addr) const;
   // Used by region verification. Checks that the contents of the
   // BOT reflect that there's a single object that spans the address
   // range [obj_start, obj_start + word_size); returns true if this is
   // the case, returns false if it's not.
   bool verify_for_object(HeapWord* obj_start, size_t word_size) const;
   void check_all_cards(size_t left_card, size_t right_card) const;
   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 };
 // A subtype of BlockOffsetArray that takes advantage of the fact
 // that its underlying space is a ContiguousSpace, so that its "active"
 // region can be more efficiently tracked (than for a non-contiguous space).
 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
   friend class VMStructs;
   // allocation boundary at which offset array must be updated
   HeapWord* _next_offset_threshold;
   size_t    _next_offset_index;      // index corresponding to that boundary
   // Work function to be called when allocation start crosses the next
   // threshold in the contig space.
   void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
     alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
                       blk_start, blk_end);
   }
   // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
   // memory first.
   void zero_bottom_entry_raw();
   // Variant of initialize_threshold that does not check for availability of the
   // memory first.
   HeapWord* initialize_threshold_raw();
  public:
   G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
   // Initialize the threshold to reflect the first boundary after the
   // bottom of the covered region.
   HeapWord* initialize_threshold();
   void reset_bot() {
     zero_bottom_entry_raw();
     initialize_threshold_raw();
   }
   // Return the next threshold, the point at which the table should be
   // updated.
   HeapWord* threshold() const { return _next_offset_threshold; }
   // These must be guaranteed to work properly (i.e., do nothing)
   // when "blk_start" ("blk" for second version) is "NULL".  In this
   // implementation, that's true because NULL is represented as 0, and thus
   // never exceeds the "_next_offset_threshold".
   void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
     if (blk_end > _next_offset_threshold)
       alloc_block_work1(blk_start, blk_end);
   }
   void alloc_block(HeapWord* blk, size_t size) {
      alloc_block(blk, blk+size);
   }
   HeapWord* block_start_unsafe(const void* addr);
   HeapWord* block_start_unsafe_const(const void* addr) const;
   void set_for_starts_humongous(HeapWord* new_top);
   virtual void print_on(outputStream* out) PRODUCT_RETURN;
 };
 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp@e7d0505c8a30 (annotated)

src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp