Adapting RCU for real-time operating system usage

• US 7,287,135 B2
• Filed: 09/29/2004
• Issued: 10/23/2007
• Est. Priority Date: 09/29/2004
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: McKenney, Paul E., Sarma, Dipankar
• Primary Examiner(s): Bragdon; Reginald
• Assistant Examiner(s): Gu; Shawn X.
• Application Number:
  US10/953,239
• Publication Number:
  US 20060090104A1
• Time in Patent Office: 1,119 Days
• Field of Search: None
• US Class Current: 711/159
• CPC Class Codes: G06F 9/5016 the resource being the memory

Abstract

A system and method is provided to support immediate freeing of a designated element from memory. Following a process of designating an element for removal from a data-structure, conditional limitations are used to determine if immediate freeing of the element from memory is available. The conditional limitations include determining that the instruction originates from a uniprocessor computer system. In addition, the conditional limitations include a determination as to whether a call_rcu primitive or synchronize_kernel primitive may be omitted, or whether the computer implemented instruction is operating in an interrupt handler. If the conditional limitations are met, the designated element may be immediately freed from memory.

Claims

1. A method for operating a single central processing unit (CPU) computer system comprising:

traversing a read-copy-update (RCU) locked data structure by a first function without a second function accessing the data structure being made aware of said traversal;

removing an element from said data structure;

determining if said element can be immediately freed from memory, including determining if said element can be removed from said data structure and freed from memory by said second function operating concurrently with said first function, and said second function passing a flag to said first function to approve immediate freeing of said element from memory in response to an ability of said second function to remove said element from said data structure and free said element from memory; and

immediately freeing said element from memory in response to a positive determination.

2. The method of claim 1, wherein the step of determining if said element can be immediately freed from memory includes determining if an interrupt handler can operate concurrently with said first function.

3. The method of claim 2, further comprising deferring freeing from memory of said element if said second function is operating in an interrupt handler and said interrupt handler is able to operate concurrently with said first function.

4. The method of claim 1, further comprising distinguishing between a uniprocessor and a multiprocessor computer system, and deferring freeing of said element in a uniprocessor computer system if said element can be removed from said data structure and freed from memory by said second function operating concurrently with said first function.

5. The method of claim 4, further comprising said second function passing a flag to said first function to determine immediate freeing of said element from memory in response to an ability of said second function concurrently operating in an interrupt handler to remove said element from said data structure and free said element from memory wherein said interrupt handler is unable to operate concurrently with said first function and remove said element from said traversed data structure.

6. A single central processing unit (CPU) computer system comprising:

a first function adapted to traverse a read-copy-update (RCU) locked data structure without awareness by a second function accessing the data structure of said traversal;

an element adapted to be removed from said data structure;

a memory manager adapted to determine if said element can be immediately freed from memory and to determine if said element can be removed from said data structure and freed from memory by said second function adapted to operate concurrently with said first function;

a flag adapted to be passed from said second function to said first function for approval of immediate freeing of said element from memory in response to an ability of said second function to remove said element from said data structure and free said element from memory; and

a removal manager adapted to immediately free said element from memory in response to receipt of a positive determination from said memory manager.

7. The system of claim 6, wherein said memory manager is adapted to determine if an interrupt handler can operate concurrently with said first function.

8. The system of claim 7, further comprising a deferral manager adapted to delay immediate freeing of said element from memory if said second function is in an interrupt handler and said interrupt handler is able to operate concurrently with said first function.

9. The system of claim 6, further comprising a system manager adapted to defer freeing of said element in a uniprocessor computer system if said element can be removed from said data structure and freed from memory by said second function operating concurrently with said first function.

10. The system of claim 9, further comprising a flag adapted to be passed from said second function to said first function to determine immediate freeing of said element from memory in response to an ability of said second function concurrently operating in an interrupt handler to remove said element from said data structure and free said element from memory, wherein said interrupt handler is unable to operate concurrently with said first function and remove said element from said traversed data structure.

11. An article comprising:

a computer-readable recordable data storage medium including computer program instructions configured to operate a single central processing unit (CPU) computer system, said instructions comprising;

instructions to traverse a read-copy-update (RCU) locked data structure by a first function without awareness by some other processes of said traversal;

instructions to remove an element from said data structure;

instructions to determine if said element can be immediately freed from memory, including instructions to determine if said element can be removed from said data structure and freed from memory by a second function concurrently operating in said data structure with said first function and instructions for said second function to pass a flag to said first function to approve immediate freeing of said element from memory in response to an ability of said second function to remove said element from said data structure and free said element from memory; and

instructions to immediately free said element from memory in response to a positive determination.

12. The article of claim 11, wherein said instructions to determine if said element can be immediately freed from memory includes instructions to determine if an interrupt handler can concurrently operate with said first function.

13. The article of claim 12, further comprising instructions to defer freeing of said element from said data structure in response to a determination of said second function operating within an interrupt handler and an ability of said interrupt handler to concurrently operate with said first function.

14. The article of claim 11, further comprising instructions to distinguish between a uniprocessor and a multiprocessor computer system, and instructions to defer freeing of said element in a uniprocessor computer system if said element can be removed from said data structure and freed from memory by a second function concurrently operating with said first function.

15. The article of claim 14, further comprising instructions for said second function to determine immediate freeing of said element from memory in response to an ability of said second function operating concurrently in an interrupt handler to remove said element from said data structure and free said element from memory, wherein said interrupt handler is unable to operate concurrently with said first function and remove said element from said traversed data structure.