Methods and systems for deadlock-free allocation of memory

• US 8,028,113 B2
• Filed: 08/15/2008
• Issued: 09/27/2011
• Est. Priority Date: 08/15/2008
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Fuente, Carlos F., Scales, William J.
• Primary Examiner(s): TSENG, CHENG YUAN
• Application Number:
  US12/192,645
• Publication Number:
  US 20100042755A1
• Time in Patent Office: 1,138 Days
• Field of Search: None
• US Class Current: 710/200
• CPC Class Codes: G06F 13/28 using burst mode transfer, e.g. direct memory access DMA, cycle steal G06F13/32 takes precedence

Abstract

Methods and systems for memory management. A method for memory management includes: maintaining a reference count for at least one first process associated with a portion of memory; maintaining a shared reference count for at least one second process associated with the portion of memory; and freeing the portion of memory when the shared reference count is decremented to zero.

Claims

1. A method for memory management, comprising:

allocating to at least one first process a first page reference to a first page of memory;

allocating to at least one second process a second page reference to a second page of memory;

copying contents of the first page to the second page;

merging sectors of the first page to the second page after the at least one second process has altered sectors of the second page;

maintaining a first reference count for the at least one first process associated with the first page of memory;

maintaining a first shared reference count for the at least one second process associated with the first page of memory, wherein the first shared reference count represents a number of non-updating processes accessing the first page;

freeing the first page of memory when the first shared reference count is decremented to zero and the first reference count equals zero;

incrementing the first shared reference count when a new non-updating process accesses the first page of memory;

decrementing the first shared reference count when an existing non-updating process terminates; and

maintaining a second reference count and a second shared reference count associated with the second page of memory, wherein the second shared reference count represents a number of non-updating processes accessing the second page of memory and is initially set to zero.

2. The method of claim 1, wherein the at least one first process comprises an updating process.

3. The method of claim 2, wherein the at least one second process comprises a non-updating process.

4. The method of claim 1, wherein the first and second reference counts and the first and second shared reference counts are maintained by a storage controller.

5. The method of claim 4, wherein:

each of the first and second portions of memory is a page, and

the first and second reference counts and the first and second shared reference counts are maintained in a page table.

6. The method of claim 4, further comprising using the first and second portions of memory in direct memory access operations.

7. The method of claim 1, wherein the freeing occurs after a merging operation.

8. A system for allocating memory resources, comprising:

a storage controller including hardware and software arranged to;

designate I/O processes as one of updating processes and non-updating processes;

allocate to the non-updating processes a first page reference to a first page of memory;

allocate to the updating processes a second page reference to a second page of memory;

copy contents of the first page to the second page;

merge sectors of the first page to the second page after the updating processes have altered sectors of the second page;

maintain a first reference count of the updating processes and a first shared reference count of the non-updating processes associated with the first page of memory;

delay freeing the first page until the first shared reference count equals zero;

increment the first shared reference count when a new non-updating process accesses the first page;

decrement the first shared reference count when an existing non-updating process terminates; and

maintain a second reference count and a second shared reference count associated with the second page, wherein the second shared reference count represents a number of non-updating processes accessing the second page and is initially set to zero.

9. The system of claim 8, wherein the storage controller comprises non-volatile memory.

10. The system of claim 8, wherein the storage controller comprises at least one hardware interface for connecting to one of a host and a disk.

11. The system of claim 8, wherein the storage controller comprises:

a memory manager;

a cache directory;

a host I/O component; and

a disk I/O component.

12. The system of claim 8, wherein the second reference count is based upon the updating processes associated with the second page.

13. The system of claim 12, wherein the second shared reference count is based upon the non-updating processes associated with the second page.

14. A computer program product comprising a tangible computer-usable medium having a computer readable program embodied in the medium, wherein the computer readable program when executed on a storage controller causes the storage controller to:

receive a first function call associated with a first process;

designate the first process as a non-updating process;

allocate to the first process a first page reference to a first page of memory;

receive a second function call associated with a second process;

designate the second process as an updating process;

copy contents of the first page to a second page of memory;

merge sectors of the first page to the second page after the second process has altered sectors of the second page; and

delay freeing the first page until the first process terminates,

wherein the delaying comprises;

maintaining a first reference count and a first shared reference count associated with the first page, and

freeing the first page when the first shared reference count equals zero,

wherein the first shared reference count represents a number of non-updating processes accessing the first page, and

wherein the computer readable program further causes the storage controller to;

increment the first shared reference count when a new non-updating process accesses the first page,

decrement the first shared reference count when an existing non-updating process terminates, and

maintain a second reference count and a second shared reference count associated with the second page, wherein the second shared reference count represents a number of non-updating processes accessing the second page and is initially set to zero.

15. The computer program product of claim 14, wherein the first and second reference counts and the first and second shared reference counts are maintained in a data structure.

16. The computer program product of claim 15, wherein the data structure comprises a page table.

18. The computer program product of claim 14, wherein the computer readable program further causes the storage controller to allocate to the second process a second page reference to the second page.

19. The computer program product of claim 14, wherein the computer readable program further causes the storage controller to:

increment the first reference count when a new updating process accesses the first page; and

decrement the first reference count when the sectors of the first page and the second page merge.

17. A method for managing memory, comprising:

providing a direct memory access storage controller that operates to;

designate I/O processes associated with a page of memory as one of updating and non-updating;

allocate to the non-updating processes a first page reference to a first page of memory;

allocate to the updating processes a second page reference to a second page of memory;

copy contents of the first page to the second page;

merge sectors of the first page to the second page after the updating processes have altered sectors of the second page;

update a first reference count representing a number of updating processes associated with the first page;

update a first shared reference count representing a total number of non-updating processes associated with the first page;

free the page for use by other code when the first shared reference count decrements to zero;

increment the first shared reference count when a new non-updating process accesses the first page; and

decrement the first shared reference count when an existing non-updating process terminates; and

maintain a second reference count and a second shared reference count associated with the second page, wherein the second shared reference count represents a number of non-updating processes accessing the second page and is initially set to zero,

wherein the storage controller comprises a combination of hardware and software.