Heal leveling

• US 9,348,748 B2
• Filed: 12/22/2014
• Issued: 05/24/2016
• Est. Priority Date: 12/24/2013
• Status: Active Grant

• Current Assignee: Macronix International Co., Ltd.
• Original Assignee: Macronix International Co., Ltd.
• Inventors: Chang, Yu-Ming, Li, Hsiang-Pang, Lue, Hang-Ting, Chang, Yuan-Hao, Kuo, Tei-Wei
• Primary Examiner(s): Verbrugge, Kevin
• Assistant Examiner(s): Otto, Alan
• Application Number:
  US14/578,820
• Publication Number:
  US 20150177996A1
• Time in Patent Office: 519 Days
• US Class Current: 1/1
• CPC Class Codes: G06F 12/00 Accessing, addressing or allocating within memory systems or architectures digital input from, or digital output to record carriers, e.g. to disk storage units, G06F3/06
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/1036 Life time enhancement
• CPC Class Codes: G06F 2212/7211 Wear leveling
• CPC Class Codes: G11C 16/3495 Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically
• CPC Class Codes: G11C 29/4401 for self repair

Abstract

Technology is described that increases endurance of memory devices through heal leveling. Heal leveling is a lightweight solution to distribute healing cycles among memory blocks. Approaches described herein can accomplish heal leveling without introducing a large amount of overhead. Heal leveling significantly improves the access performance and the effective lifetime of memory blocks. By more evenly distributing the heal count it may not be necessary to directly apply wear leveling based on access counts of each block because each block will be more evenly accessed in the long run. Heal leveling may be performed by moving data that is seldom or never modified after creation, such as read-only files, to blocks having suffered the greatest number, or a high number, of healing cycles.

Claims

1. A method for operating a memory device having a plurality of memory blocks, comprising:

maintaining heal counts for memory blocks in the plurality of memory blocks;

in combination with an access cycle of a first block having a first heal count, finding a second block having a second heal count lower than the first heal count, and causing the data from the second block to be copied to the first block.

2. The method of claim 1, including maintaining access cycle counts for memory blocks in the plurality of memory blocks, issuing heal commands to the memory device for blocks reaching a threshold number of access cycles, and incrementing the heal counts.

3. The method of claim 2, wherein the memory is flash memory, and the access cycles are erase cycles.

4. The method of claim 1, including monitoring heal status indicator values for memory blocks in the plurality of memory blocks, issuing heal commands to the memory device for blocks reaching a threshold heal status indicator value, and incrementing the heal counts.

5. The method of claim 1, wherein said finding a second block includes selecting a least recently cleared block as said second block from a number of blocks with said second heal count.

6. The method of claim 1, including maintaining a data structure classifying blocks in the plurality of blocks by heal count.

7. The method of claim 1, including maintaining a set of lists of entries for blocks in the plurality of blocks, assigning heal count thresholds to the linked lists in the set, and inserting entries for the blocks into the linked lists in the set according to the heal counts of the blocks and the heal count thresholds.

8. The method of claim 7, wherein the set of lists includes a number N members, where N is greater than 2, and maintaining a base pointer identifying a starting list in the set having a starting heal count threshold, and wherein other lists in the set are addressable by corresponding offsets 1 to N−

1 (modulo N) from the base pointer.

9. The method of claim 8, including identifying the first block having the first heal count by detecting an access cycle for a block in a list in the set having offset N−

1 (modulo N) from the base pointer.

10. The method of claim 8, wherein if the list pointed to by the base pointer becomes empty, incrementing the base pointer modulo N.

11. The method of claim 8, including ordering the lists to identify blocks in the respective lists least recently subject of an access cycle, and wherein said finding the second block includes identifying the block identified as least recently subject of an access cycle in the list with the lowest index having a valid block.

12. The method of claim 11, wherein the lists in the set are linked lists, having the block least recently subject of an access cycle at an end of the linked list.

13. A system comprising:

memory including a plurality of memory blocks, the memory being configured for heal cycles;

a processor coupled to the memory, including logic to;

maintain heal counts for memory blocks in the plurality of memory blocks;

in combination with an access cycle of a first block having a first heal count, find a second block having a second heal count lower than the first heal count, and cause the data from the second block to be copied to the first block.

14. The system of claim 13, wherein the processor includes logic to maintain access cycle counts for memory blocks in the plurality of memory blocks, issue heal commands to the memory device for blocks reaching a threshold number of access cycles, and increment the heal counts.

15. The system of claim 14, wherein the memory is flash memory, and the access cycles are erase cycles.

16. The system of claim 13, wherein the processor includes logic to monitor heal status indicator values for memory blocks in the plurality of memory blocks, issue heal commands to the memory device for blocks reaching a threshold heal status indicator value, and increment the heal counts.

17. The system of claim 13, wherein said logic to find a second block includes logic to select a least recently cleared block as said second block from a number of blocks with said second heal count.

18. The system of claim 13, wherein the processor includes logic to maintain a data structure classifying blocks in the plurality of blocks by heal count.

19. The system of claim 13, wherein the processor includes logic to maintain a set of lists of entries for blocks in the plurality of blocks, assign heal count thresholds to the linked lists in the set, and insert entries for the blocks into the linked lists in the set according to the heal counts of the blocks and the heal count thresholds.

20. The system of claim 19, wherein the set of lists includes a number N members, where N is greater than 2, and wherein the processor includes logic to maintain a base pointer identifying a starting list in the set having a starting heal count threshold, and wherein other lists in the set are addressable by corresponding offsets 1 to N−

1 (modulo N) from the base pointer.

21. The system of claim 20, wherein the processor includes logic to identify the first block having the first heal count by detecting an access cycle for a block in a list in the set having offset N−

1 (modulo N) from the base pointer.

22. The system of claim 20, wherein the processor includes logic to increment the base pointer modulo N wherein if the list pointed to by the base pointer becomes empty.

23. The system of claim 20, wherein the processor includes logic to order the lists to identify blocks in the respective lists least recently subject of an access cycle, and wherein said logic to find the second block includes logic to identify the block identified as least recently subject of an access cycle in the list with the lowest index having a valid block.

24. The system of claim 23, wherein the lists in the set are linked lists, having the block least recently subject of an access cycle at an end of the linked list.