Caching mechanism for a virtual heap

• US 20040168030A1
• Filed: 02/20/2004
• Published: 08/26/2004
• Est. Priority Date: 06/02/2000
• Status: Active Grant

• Current Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Slaughter, Gregory L., Saulpaugh, Thomas E., Traversat, Bernard A., Duigou, Michael J.
• Granted Patent: US 6,874,066 B2
• Time in Patent Office: Days
• US Class Current: 711/133
• CPC Class Codes: G06F 12/0276 Generational garbage collection
• CPC Class Codes: G06F 9/45504 Abstract machines for programme code execution, e.g. Java virtual machine [JVM], interpreters, emulators
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99957 Garbage collection

Abstract

A caching mechanism for a virtual persistent heap. A feature of a virtual persistent heap is the method used to cache portions of the virtual persistent heap into the physical heap. The caching mechanism may be effective with small consumer and appliance devices that typically have a small amount of memory and that may be using flash devices as persistent storage. In the caching mechanism, the virtual persistent heap may be divided into cache lines. A cache line is the smallest amount of virtual persistent heap space that can be loaded or flushed at one time. Caching in and caching out operations are used to load cache lines into the heap or to flush dirty cache lines into the store. Different cache line sizes may be used for different regions of the heap. Translation between a virtual persistent heap address and the heap may be simplified by the caching mechanism.

Claims

1. A method for managing a virtual heap in a virtual machine executing within a device, the method comprising:

executing a process within the virtual machine;

providing the virtual heap for the process, wherein the virtual heap comprises a store heap comprising a first plurality of cache lines for storing objects for the process, and wherein the virtual heap further comprises an in-memory heap comprising a second plurality of cache lines for caching objects for access by the process during execution, and wherein the store heap and the in-memory heap are comprised in one memory address space, and wherein a cache line is the smallest addressable unit of memory within the memory address space comprising the store heap and the in-memory heap;

caching objects for the process executing within the virtual machine in the in-memory heap;

the process modifying a first one of the objects for the process in a first cache line in the in-memory heap; and

flushing the first cache line from the in-memory heap to the store heap subsequent to said modifying the first one of the objects.

2. The method of claim 1,

wherein said flushing the first cache line from the in-memory heap to the store heap comprises:

moving the first cache line from the in-memory heap to a cache I/O buffer, wherein the cache I/O buffer is configured to store modified cache lines from the in-memory heap; and

writing one or more of the modified cache lines, including the first cache line, from the cache I/O buffer to the store heap.

3. The method of claim 2,

wherein said writing the one or more of the modified cache lines, including the first cache line, from the cache I/O buffer to the store heap comprises:

overwriting the first cache line in the store heap with the first cache line from the cache I/O buffer.

4. The method of claim 1,

wherein the in-memory heap comprises a plurality of regions, wherein each region comprises one or more of the second plurality of cache lines;

the method further comprising;

the process creating, in a first region of the plurality of regions in the in-memory heap, a new object;

moving the new object from the first region of the in-memory heap to a second region of the in-memory heap; and

flushing the second region of the in-memory heap including the new object to the store heap.

5. The method of claim 1,

wherein the objects for the process comprise code and data for use by the process during execution within the virtual machine.

6. The method of claim 1,

wherein the store heap is one of a plurality of store heaps in a persistent store;

wherein each of the plurality of store heaps is associated with one of a plurality of processes;

wherein the process is one of the plurality of processes.

7. The method of claim 1,

wherein the store heap is comprised in a non-volatile memory coupled to the device.

8. The method of claim 7,

wherein the non-volatile memory is a flash memory addressable in block writes, wherein a block write is of a fixed amount of the flash memory, wherein the fixed amount of the flash memory is a block write size;

and

wherein the first plurality of cache lines in the store heap and the second plurality of cache lines in the in-memory heap are of the block write size of the flash memory.

9. The method of claim 1,

wherein the device is a mobile computing device.

10. The method of claim 1,

wherein the virtual machine is a Java virtual machine;

and wherein the process is a Java application.

11. The method of claim 1,

wherein a cache line comprises one or more objects;

and

wherein the cache line is the smallest unit of memory moved between the in-memory heap and the store heap.

12. A system comprising:

a device configured to execute a virtual machine, wherein the virtual machine is configured to execute a process;

a first memory coupled to the device, wherein the first memory is configured to store a store heap for the process, and wherein the store heap is comprised within a virtual heap for the process, and wherein the store heap comprises a first plurality of cache lines for storing objects for the process;

a second memory coupled to the device, wherein the second memory is configured to store an in-memory heap for the process, and wherein the in-memory heap is comprised within the virtual heap, and wherein the in-memory heap comprises a second plurality of cache lines for caching objects for access by the process during execution;

wherein the store heap and the in-memory heap are comprised in one memory address space, and wherein a cache line is the smallest addressable unit of memory within the memory address space comprising the store heap and the in-memory heap;

wherein the device is further configured to execute a virtual machine virtual memory manager, wherein the virtual machine virtual memory manager is configured to;

cache objects for the process executing within the virtual machine in the in-memory heap;

wherein the process is configured to;

modify a first one of the objects for the process in a first cache line in the in-memory heap; and

wherein the virtual machine virtual memory manager is further configured to;

flush the first cache line from the in-memory heap to the store heap subsequent to said modifying the first one of the objects.

13. The system of claim 12,

wherein, in flushing the first cache line from the in-memory heap to the store heap, the virtual machine virtual memory manager is further configured to:

move the first cache line from the in-memory heap to a cache I/O buffer, herein the cache I/O buffer is configured to store modified cache lines from the in-memory heap; and

write one or more of the modified cache lines, including the first cache line, from the cache I/O buffer to the store heap.

14. The system of claim 13,

wherein, in writing the one or more of the modified cache lines, including the first cache line, from the cache I/O buffer to the store heap, the virtual machine virtual memory manager is further configured to:

overwrite the first cache line in the store heap with the first cache line from the cache I/O buffer.

15. The system of claim 12,

wherein the in-memory heap comprises a plurality of regions, wherein each region comprises one or more of the second plurality of cache lines;

wherein the process is further configured to;

create, in a first region of the plurality of regions in the in-memory heap, a new object; and

wherein the virtual machine virtual memory manager is further configured to;

move the new object from the first region of the in-memory heap to a second region of the in-memory heap; and

flush the second region of the in-memory heap including the new object to the store heap.

16. The system of claim 12,

wherein the objects for the process comprise code and data for use by the process during execution within the virtual machine.

17. The system of claim 12,

wherein the first memory comprises a persistent store configured to store a plurality of store heaps, and wherein each of the plurality of store heaps is associated with one of a plurality of processes, and wherein the store heap for the process is one of the plurality of store heaps, and wherein the process is one of the plurality of processes.

18. The system of claim 12,

wherein the first memory is a flash memory addressable in block writes, wherein a block write is of a fixed amount of the flash memory, wherein the fixed amount of the flash memory is a block write size;

and

wherein the first plurality of cache lines in the store heap and the second plurality of cache lines in the in-memory heap are of the block write size of the flash memory.

19. The system of claim 12,

wherein the device is a mobile computing device.

20. The system of claim 12,

wherein the virtual machine is a Java virtual machine;

and wherein the process is a Java application.

21. The system of claim 12,

wherein a cache line comprises one or more objects;

and

wherein the cache line is the smallest unit of memory moved between the in-memory heap and the store heap.

22. A carrier medium comprising programming instructions executable to manage a virtual heap on a virtual machine executing within a device, wherein the program instructions are executable to implement:

providing the virtual heap for a process executing within the virtual machine, wherein the virtual heap comprises a store heap comprising a first plurality of cache lines for storing objects for the process, and wherein the virtual heap further comprises an in-memory heap comprising a second plurality of cache lines for caching objects for access by the process during execution, and wherein the store heap and the in-memory heap are comprised in one memory address space, and wherein a cache line is the smallest addressable unit of memory within the memory address space comprising the store heap and the in-memory heap;

caching objects for the process executing within the virtual machine in the in-memory heap; and

flushing a first cache line from the in-memory heap to the store heap subsequent to the process modifying a first one of the objects for the process in the first cache line in the in-memory heap.

23. The carrier medium of claim 22,

wherein, in flushing the first cache line from the in-memory heap to the store heap, the program instructions are further executable to implement:

moving the first cache line from the in-memory heap to a cache I/O buffer, wherein the cache I/O buffer is configured to store modified cache lines from the in-memory heap; and

writing one or more of the modified cache lines, including the first cache line, from the cache I/O buffer to the store heap.

24. The carrier medium of claim 22,

wherein the in-memory heap comprises a plurality of regions, wherein each region comprises one or more of the second plurality of cache lines;

wherein the program instructions are further executable to implement;

moving a new object, created by the process in a first region of the plurality of regions in the in-memory heap, from the first region of the in-memory heap to a second region of the in-memory heap; and

flushing the second region of the in-memory heap including the new object to the store heap.

25. The carrier medium of claim 22,

wherein the store heap is one of a plurality of store heaps in a persistent store;

wherein each of the plurality of store heaps is associated with one of a plurality of processes;

wherein the process is one of the plurality of processes.

26. The carrier medium of claim 22,

wherein the store heap is comprised in a flash memory coupled to the device;

wherein the flash memory is addressable in block writes, wherein a block write is of a fixed amount of the flash memory, wherein the fixed amount of the flash memory is a block write size; and

wherein the first plurality of cache lines in the store heap and the second plurality of cache lines in the in-memory heap are of the block write size of the flash memory.

27. The carrier medium of claim 22,

wherein the device is a mobile computing device;

and

wherein the virtual machine is a Java virtual machine; and

wherein the process is a Java application.

28. The carrier medium of claim 22,

wherein a cache line comprises one or more objects;

and wherein the cache line is the smallest unit of memory moved between the in-memory heap and the store heap.