Mercurial > hg > truffle
diff src/share/vm/services/g1MemoryPool.hpp @ 1089:db0d5eba9d20
6815790: G1: Missing MemoryPoolMXBeans with -XX:+UseG1GC
Summary: It introduces the necessary memory pools for G1.
Reviewed-by: mchung, ysr
author | tonyp |
---|---|
date | Fri, 20 Nov 2009 14:47:01 -0500 |
parents | |
children | ed52bcc32739 |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/services/g1MemoryPool.hpp Fri Nov 20 14:47:01 2009 -0500 @@ -0,0 +1,226 @@ +/* + * Copyright (c) 2007 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. + * + */ + +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. Right now, we set +// that the committed size for the eden and the 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 +// +// 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: + G1CollectedHeap* _g1h; + + // 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: + // Would only be called from subclasses. + G1MemoryPoolSuper(G1CollectedHeap* g1h, + const char* name, + size_t init_size, + size_t max_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 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 eden_space_max(G1CollectedHeap* g1h); + + static size_t survivor_space_committed(G1CollectedHeap* g1h); + static size_t survivor_space_used(G1CollectedHeap* g1h); + static size_t survivor_space_max(G1CollectedHeap* g1h); + + static size_t old_space_committed(G1CollectedHeap* g1h); + static size_t old_space_used(G1CollectedHeap* g1h); + static size_t old_space_max(G1CollectedHeap* g1h); + + // The non-static versions are included for convenience. + + size_t eden_space_committed() { + return eden_space_committed(_g1h); + } + size_t eden_space_used() { + return eden_space_used(_g1h); + } + size_t eden_space_max() { + return eden_space_max(_g1h); + } + + size_t survivor_space_committed() { + return survivor_space_committed(_g1h); + } + size_t survivor_space_used() { + return survivor_space_used(_g1h); + } + size_t survivor_space_max() { + return survivor_space_max(_g1h); + } + + size_t old_space_committed() { + return old_space_committed(_g1h); + } + size_t old_space_used() { + return old_space_used(_g1h); + } + size_t old_space_max() { + return old_space_max(_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(); + } + size_t max_size() { + return eden_space_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(); + } + size_t max_size() { + return survivor_space_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(); + } + size_t max_size() { + return old_space_max(); + } + MemoryUsage get_memory_usage(); +};