jdk8-mips64-public/hotspot: src/share/vm/services/g1MemoryPool.hpp@17c778814856 (annotated)

src/share/vm/services/g1MemoryPool.hpp@17c778814856 (annotated)

src/share/vm/services/g1MemoryPool.hpp

Fri, 14 Jan 2011 13:47:53 -0500

author: coleenp
date: Fri, 14 Jan 2011 13:47:53 -0500
changeset 2463: 17c778814856
parent 2314: f95d63e2154a
child 2821: b52782ae3880
permissions: -rw-r--r--

6811367: Fix code in HeapDumper::dump_heap() to avoid buffer overrun
Summary: Check buffer size before using and use dynamic buffer sizes for subsequent calls.
Reviewed-by: kamg, dholmes

 /*
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  * 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
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 #ifndef SHARE_VM_SERVICES_G1MEMORYPOOL_HPP
 #define SHARE_VM_SERVICES_G1MEMORYPOOL_HPP
 #ifndef SERIALGC
 #include "services/memoryPool.hpp"
 #include "services/memoryUsage.hpp"
 #endif
 class G1CollectedHeap;
 // This file contains the three classes that represent the memory
 // pools of the G1 spaces: G1EdenPool, G1SurvivorPool, and
 // G1OldGenPool. In G1, unlike our other GCs, we do not have a
 // physical space for each of those spaces. Instead, we allocate
 // regions for all three spaces out of a single pool of regions (that
 // pool basically covers the entire heap). As a result, the eden,
 // survivor, and old gen are considered logical spaces in G1, as each
 // is a set of non-contiguous regions. This is also reflected in the
 // way we map them to memory pools here. The easiest way to have done
 // this would have been to map the entire G1 heap to a single memory
 // pool. However, it's helpful to show how large the eden and survivor
 // get, as this does affect the performance and behavior of G1. Which
 // is why we introduce the three memory pools implemented here.
 //
 // The above approach inroduces a couple of challenging issues in the
 // implementation of the three memory pools:
 //
 // 1) The used space calculation for a pool is not necessarily
 // independent of the others. We can easily get from G1 the overall
 // used space in the entire heap, the number of regions in the young
 // generation (includes both eden and survivors), and the number of
 // survivor regions. So, from that we calculate:
 //
 //  survivor_used = survivor_num * region_size
 //  eden_used     = young_region_num * region_size - survivor_used
 //  old_gen_used  = overall_used - eden_used - survivor_used
 //
 // Note that survivor_used and eden_used are upper bounds. To get the
 // actual value we would have to iterate over the regions and add up
 // ->used(). But that'd be expensive. So, we'll accept some lack of
 // accuracy for those two. But, we have to be careful when calculating
 // old_gen_used, in case we subtract from overall_used more then the
 // actual number and our result goes negative.
 //
 // 2) Calculating the used space is straightforward, as described
 // above. However, how do we calculate the committed space, given that
 // we allocate space for the eden, survivor, and old gen out of the
 // same pool of regions? One way to do this is to use the used value
 // as also the committed value for the eden and survivor spaces and
 // then calculate the old gen committed space as follows:
 //
 //  old_gen_committed = overall_committed - eden_committed - survivor_committed
 //
 // Maybe a better way to do that would be to calculate used for eden
 // and survivor as a sum of ->used() over their regions and then
 // calculate committed as region_num * region_size (i.e., what we use
 // to calculate the used space now). This is something to consider
 // in the future.
 //
 // 3) Another decision that is again not straightforward is what is
 // the max size that each memory pool can grow to. One way to do this
 // would be to use the committed size for the max for the eden and
 // survivors and calculate the old gen max as follows (basically, it's
 // a similar pattern to what we use for the committed space, as
 // described above):
 //
 //  old_gen_max = overall_max - eden_max - survivor_max
 //
 // Unfortunately, the above makes the max of each pool fluctuate over
 // time and, even though this is allowed according to the spec, it
 // broke several assumptions in the M&M framework (there were cases
 // where used would reach a value greater than max). So, for max we
 // use -1, which means "undefined" according to the spec.
 //
 // 4) Now, there is a very subtle issue with all the above. The
 // framework will call get_memory_usage() on the three pools
 // asynchronously. As a result, each call might get a different value
 // for, say, survivor_num which will yield inconsistent values for
 // eden_used, survivor_used, and old_gen_used (as survivor_num is used
 // in the calculation of all three). This would normally be
 // ok. However, it's possible that this might cause the sum of
 // eden_used, survivor_used, and old_gen_used to go over the max heap
 // size and this seems to sometimes cause JConsole (and maybe other
 // clients) to get confused. There's not a really an easy / clean
 // solution to this problem, due to the asynchrounous nature of the
 // framework.
 // This class is shared by the three G1 memory pool classes
 // (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we
 // calculate used / committed bytes for these three pools is related
 // (see comment above), we put the calculations in this class so that
 // we can easily share them among the subclasses.
 class G1MemoryPoolSuper : public CollectedMemoryPool {
 private:
   // It returns x - y if x > y, 0 otherwise.
   // As described in the comment above, some of the inputs to the
   // calculations we have to do are obtained concurrently and hence
   // may be inconsistent with each other. So, this provides a
   // defensive way of performing the subtraction and avoids the value
   // going negative (which would mean a very large result, given that
   // the parameter are size_t).
   static size_t subtract_up_to_zero(size_t x, size_t y) {
     if (x > y) {
       return x - y;
     } else {
       return 0;
     }
   }
 protected:
   G1CollectedHeap* _g1h;
   // Would only be called from subclasses.
   G1MemoryPoolSuper(G1CollectedHeap* g1h,
                     const char* name,
                     size_t init_size,
                     bool support_usage_threshold);
   // The reason why all the code is in static methods is so that it
   // can be safely called from the constructors of the subclasses.
   static size_t undefined_max() {
     return (size_t) -1;
   }
   static size_t overall_committed(G1CollectedHeap* g1h) {
     return g1h->capacity();
   }
   static size_t overall_used(G1CollectedHeap* g1h) {
     return g1h->used_unlocked();
   }
   static size_t eden_space_committed(G1CollectedHeap* g1h);
   static size_t eden_space_used(G1CollectedHeap* g1h);
   static size_t survivor_space_committed(G1CollectedHeap* g1h);
   static size_t survivor_space_used(G1CollectedHeap* g1h);
   static size_t old_space_committed(G1CollectedHeap* g1h);
   static size_t old_space_used(G1CollectedHeap* g1h);
 };
 // Memory pool that represents the G1 eden.
 class G1EdenPool : public G1MemoryPoolSuper {
 public:
   G1EdenPool(G1CollectedHeap* g1h);
   size_t used_in_bytes() {
     return eden_space_used(_g1h);
   }
   size_t max_size() const {
     return undefined_max();
   }
   MemoryUsage get_memory_usage();
 };
 // Memory pool that represents the G1 survivor.
 class G1SurvivorPool : public G1MemoryPoolSuper {
 public:
   G1SurvivorPool(G1CollectedHeap* g1h);
   size_t used_in_bytes() {
     return survivor_space_used(_g1h);
   }
   size_t max_size() const {
     return undefined_max();
   }
   MemoryUsage get_memory_usage();
 };
 // Memory pool that represents the G1 old gen.
 class G1OldGenPool : public G1MemoryPoolSuper {
 public:
   G1OldGenPool(G1CollectedHeap* g1h);
   size_t used_in_bytes() {
     return old_space_used(_g1h);
   }
   size_t max_size() const {
     return undefined_max();
   }
   MemoryUsage get_memory_usage();
 };
 #endif // SHARE_VM_SERVICES_G1MEMORYPOOL_HPP

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/services/g1MemoryPool.hpp@17c778814856 (annotated)

src/share/vm/services/g1MemoryPool.hpp